leetcode-java
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20 hours ago •
cheehwatang
cheehwatang
💻 Detailed Explanations for LeetCode Solutions in Java. Updated Daily.
LeetCode Java Solutions
Hi 👋, I'm Chee Hwa and welcome to LeetCode Solutions in Java.
As I'm new to LeetCode and programming in general, I'm practicing everyday and hope to share my solutions and learnings with you.
- Exclusively on Java
- Beginner problems
- Daily Challenge if within my ability
Latest Solutions
| Date | Problem | Difficulty | Solution | Topics |
|---|---|---|---|---|
| September 14th | 1775. Equal Sum Arrays With Minimum Number of Operations | $\text{\color{Dandelion}Medium}$ | Counting | Array, Counting, Greedy |
| September 13th | 1814. Count Nice Pairs in an Array | $\text{\color{Dandelion}Medium}$ | Counting & Hash Table | Array, Counting, Hash Table, Math |
| September 12th | 2006. Count Number of Pairs With Absolute Difference K | $\text{\color{TealBlue}Easy}$ | Hash Table | Array, Hash Table |
| September 11th | 2006. Count Number of Pairs With Absolute Difference K | $\text{\color{TealBlue}Easy}$ | Counting | Array, Counting |
| September 10th | 2006. Count Number of Pairs With Absolute Difference K | $\text{\color{TealBlue}Easy}$ | Brute Force | Array |
Topics
The problem sets and solutions are grouped into Topics as stated in LeetCode.
- Array
- Backtracking
- Binary Search
- Binary Search Tree
- Binary Tree
- Bit Manipulation
- Brainteaser
- Breadth-First Search
- Bucket Sort
- Counting
- Counting Sort
- Data Stream
- Depth-First Search
- Design
- Divide and Conquer
- Dynamic Programming
- Enumeration
- Geometry
- Graph
- Greedy
- Hash Table
- Heap (Priority Queue)
- Interactive
- Linked List
- Math
- Matrix
- Memoization
- Monotonic Stack
- Number Theory
- Ordered Set
- Prefix Sum
- Queue
- Recursion
- Simulation
- Sliding Window
- Sorting
- Stack
- String
- Tree
- Two Pointers
- Union Find
Array
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 1 | Two Sum | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table | |
| 15 | 3Sum | Java | $\text{\color{Dandelion}Medium}$ | Array, Sorting, Two Pointers | |
| 16 | 3Sum Closest | Java | $\text{\color{Dandelion}Medium}$ | Array, Sorting, Two Pointers | |
| 26 | Remove Duplicates from Sorted Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Two Pointers | |
| 27 | Remove Element | Java | $\text{\color{TealBlue}Easy}$ | Array, Two Pointers | |
| 36 | Valid Sudoku | Java without or with Hash Table | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Matrix | |
| 37 | Sudoku Solver | Java | $\text{\color{Red}Hard}$ | Array, Backtracking, Matrix | |
| 45 | Jump Game II | Dynamic Programming (Memoization), Dynamic Programming (Tabulation) or Greedy | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Greedy | |
| 46 | Permutations | Java with Backtracking, Iteration or Recursion | $\text{\color{Dandelion}Medium}$ | Array, Backtracking | |
| 49 | Group Anagrams | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting, String | |
| 55 | Jump Game | Java with Dynamic Programming or Greedy | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Greedy | |
| 57 | Insert Interval | Java | $\text{\color{Dandelion}Medium}$ | Array | |
| 73 | Set Matrix Zeroes | Java with Array, Hash Table or In-Place | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Matrix | |
| 79 | Word Search | Java | $\text{\color{Dandelion}Medium}$ | Array, Backtracking, Matrix | |
| 80 | Remove Duplicates from Sorted Array II | Java | $\text{\color{Dandelion}Medium}$ | Array, Two Pointers | |
| 88 | Merge Sorted Array | Java with Sorting or Two Pointers | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | |
| 121 | Best Time to Buy and Sell Stock | Java with or without Dynamic Programming | $\text{\color{TealBlue}Easy}$ | Array, Dynamic Programming | |
| 130 | Surrounded Regions | Java with Breadth-First Search, Depth-First Search or Union Find | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Depth-First Search, Matrix, Union Find | |
| 134 | Gas Station | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy | |
| 136 | Single Number | Java | $\text{\color{TealBlue}Easy}$ | Array, Bit Manipulation | Stream Reduce |
| 152 | Maximum Product Subarray | Java with Array or Dynamic Programming | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming | |
| 167 | Two Sum II - Input Array is Sorted | Java with Binary Search or Two Pointers | $\text{\color{Dandelion}Medium}$ | Array, Binary Search, Two Pointers | |
| 169 | Majority Element | Java with Boyer-Moore Majority Voting Algorithm, Counting & Divide and Conquer, Counting & Hash Table or Sorting | $\text{\color{TealBlue}Easy}$ | Array, Counting, Divide and Conquer, Hash Table, Sorting | |
| 200 | Number of Islands | Java with Breadth-First Search, Depth-First Search or Union Find | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Depth-First Search, Matrix, Union Find | |
| 217 | Contains Duplicate | Java with Hash Map, Hash Set or Sorting | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Sorting | |
| 219 | Contains Duplicate II | Java with Hash Map or Sliding Window | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Sliding Window | |
| 220 | Contains Duplicate III | Java with Sliding Window & Bucket Sort, Sliding Window & Ordered Set or Sorting | $\text{\color{Red}Hard}$ | Array, Bucket Sort, Ordered Set, Sliding Window, Sorting | |
| 228 | Summary Ranges | Java | $\text{\color{TealBlue}Easy}$ | Array | |
| 229 | Majority Element II | Java with Boyer-Moore Majority Voting Algorithm, Counting & Hash Table or Sorting | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Sorting | |
| 238 | Product of Array Except Self | Java | $\text{\color{Dandelion}Medium}$ | Array, Prefix Sum | |
| 274 | H-Index | Java with Counting Sort and Sorting | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Sorting | |
| 275 | H-Index II | Java | $\text{\color{Dandelion}Medium}$ | Array, Binary Search | |
| 283 | Move Zeroes | Java | $\text{\color{TealBlue}Easy}$ | Array, Two Pointers | |
| 334 | Increasing Triplet Subsequence | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy | |
| 368 | Largest Divisible Subset | Java | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Math, Sorting | |
| 393 | UTF-8 Validation | Java without or with Bit Manipulation | $\text{\color{Dandelion}Medium}$ | Array, Bit Manipulation | |
| 414 | Third Maximum Number | Java with Sorting, without Sorting or with Hash Table & Priority Queue | $\text{\color{TealBlue}Easy}$ | Array, Sorting | |
| 448 | Find All Numbers Disappeared in an Array | Java with or without Hash Table | $\text{\color{TealBlue}Easy}$ | Array, Hash Table | |
| 485 | Maximum Consecutive Ones | Java | $\text{\color{TealBlue}Easy}$ | Array | |
| 496 | Next Greater Element I | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Monotonic Stack, Stack | |
| 503 | Next Greater Element II | Java | $\text{\color{Dandelion}Medium}$ | Array, Monotonic Stack, Stack | |
| 523 | Continuous Subarray Sum | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Math, Prefix Sum | |
| 560 | Subarray Sum Equals K | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Prefix Sum | |
| 561 | Array Partition | Java with Greedy & Counting Sort or Greedy & Sorting | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Greedy, Sorting | |
| 609 | Find Duplicate File in System | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, String | |
| 645 | Set Mismatch | Java with Bit Manipulation, Hash Table or Sorting | $\text{\color{TealBlue}Easy}$ | Array, Bit Manipulation, Hash Table, Sorting | |
| 713 | Subarray Product Less Than K | Java | $\text{\color{Dandelion}Medium}$ | Array, Sliding Window | |
| 744 | Find Smallest Letter Greater Than Target | Java with Linear Search or Binary Search | $\text{\color{TealBlue}Easy}$ | Array, Binary Search | |
| 746 | Min Cost Climbing Stairs | Java with Dynamic Programming - Tabulation or Memoization | $\text{\color{TealBlue}Easy}$ | Array, Dynamic Programming | |
| 766 | Toeplitz Matrix | Java | $\text{\color{TealBlue}Easy}$ | Array, Matrix | Follow up: One Row at a Time and One Column at a Time |
| 812 | Largest Triangle Area | Java | $\text{\color{TealBlue}Easy}$ | Array, Geometry, Math | |
| 835 | Image Overlap | Java with Bit Manipulation or Hash Table | $\text{\color{Dandelion}Medium}$ | Array, Matrix | |
| 904 | Fruit Into Baskets | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sliding Window | |
| 905 | Sort Array By Parity | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | |
| 922 | Sort Array By Parity II | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | |
| 923 | 3Sum With Multiplicity | Java with Counting Hash Table or Sorting & Two Pointers | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Sorting, Two Pointers | |
| 929 | Unique Email Addresses | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, String | |
| 941 | Valid Mountain Array | Java | $\text{\color{TealBlue}Easy}$ | Array | |
| 944 | Delete Columns to Make Sorted | Java | $\text{\color{TealBlue}Easy}$ | Array, String | |
| 948 | Bag of Tokens | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Sorting, Two Pointers | |
| 953 | Verifying an Alien Dictionary | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, String | |
| 974 | Subarray Sums Divisible by K | Java with Counting or Hash Table | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Prefix Sum | |
| 976 | Largest Perimeter Triangle | Java | $\text{\color{TealBlue}Easy}$ | Array, Greedy, Math, Sorting | |
| 977 | Squares of a Sorted Array | Java with Sorting or Two Pointers | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | |
| 985 | Sum of Even Numbers After Queries | Java | $\text{\color{Dandelion}Medium}$ | Array, Simulation | |
| 989 | Add to Array-Form of Integer | Java | $\text{\color{TealBlue}Easy}$ | Array, Math | |
| 1019 | Next Greater Node In Linked List | Java | $\text{\color{Dandelion}Medium}$ | Array, Linked List, Monotonic Stack, Stack | |
| 1037 | Valid Boomerang | Java | $\text{\color{TealBlue}Easy}$ | Array, Geometry, Math | |
| 1051 | Height Checker | Java with Counting Sort or Sorting | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Sorting | |
| 1089 | Duplicate Zeros | Java without or with Two Pointers | $\text{\color{TealBlue}Easy}$ | Array, Two Pointers | |
| 1122 | Relative Sort Array | Java with Counting Sort or Hash Table | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Hash Table, Sorting | |
| 1207 | Unique Number of Occurrences | Java with Counting & Sorting or Hash Table | $\text{\color{TealBlue}Easy}$ | Array, Hash Table | |
| 1232 | Check If It Is a Straight Line | Java | $\text{\color{TealBlue}Easy}$ | Array, Geometry, Math | |
| 1239 | Maximum Length of a Concatenated String with Unique Characters | Java with Backtracking or Bit Manipulation | $\text{\color{Dandelion}Medium}$ | Array, Backtracking, Bit Manipulation, String | |
| 1295 | Find Numbers with Even Number of Digits | Java | $\text{\color{TealBlue}Easy}$ | Array | |
| 1299 | Replace Elements with Greatest Element on Right Side | Java | $\text{\color{TealBlue}Easy}$ | Array | |
| 1337 | The K Weakest Rows in a Matrix | Java with Linear Search, Binary Search, Heap (Priority Queue) & Binary Search or Sorting & Binary Search | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Heap (Priority Queue), Matrix, Sorting | |
| 1346 | Check If N and Its Double Exist | Java with Binary Search & Sorting, Hash Table or Two Pointers | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Hash Table, Sorting, Two Pointers | |
| 1351 | Count Negative Numbers in a Sorted Matrix | Java with Linear Search or Binary Search | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Matrix | |
| 1470 | Shuffle the Array | Java | $\text{\color{TealBlue}Easy}$ | Array | |
| 1480 | Running Sum of 1D Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Prefix Sum | |
| 1497 | Check If Array Pairs Are Divisible by k | Java with Counting or Hash Table | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table | |
| 1534 | Count Good Triplets | Java | $\text{\color{TealBlue}Easy}$ | Array, Enumeration | |
| 1578 | Minimum Time to Make Rope Colorful | Java with Dynamic Programming or Greedy | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Greedy, String | |
| 1636 | Sort Array by Increasing Frequency | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Sorting | |
| 1662 | Check If Two String Arrays are Equivalent | Java with or without Pointers | $\text{\color{TealBlue}Easy}$ | Array, String | |
| 1672 | Richest Customer Wealth | Java | $\text{\color{TealBlue}Easy}$ | Array, Matrix | |
| 1679 | Max Number of K-Sum Pairs | Java with Hash Table or Sorting & Two Pointers | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting, Two Pointers | |
| 1711 | Count Good Meals | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table | |
| 1732 | Find the Highest Altitude | Java | $\text{\color{TealBlue}Easy}$ | Array, Prefix Sum | |
| 1775 | Equal Sum Arrays With Minimum Number of Operations | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy | |
| 1814 | Count Nice Pairs in an Array | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Math | |
| 1833 | Maximum Ice Cream Bars | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Sorting | |
| 1834 | Single-Threaded CPU | Java | $\text{\color{Dandelion}Medium}$ | Array, Heap (Priority Queue), Sorting | |
| 1865 | Finding Pairs With a Certain Sum | Java | $\text{\color{Dandelion}Medium}$ | Array, Design, Hash Table | |
| 1920 | Build Array from Permutation | Java | $\text{\color{TealBlue}Easy}$ | Array, Simulation | |
| 1926 | Nearest Exit from Entrance in Maze | Java | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Matrix | |
| 1962 | Remove Stones to Minimize the Total | Java | $\text{\color{Dandelion}Medium}$ | Array, Heap (Priority Queue) | |
| 1979 | Find Greatest Common Divisor of Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Math, Number Theory | |
| 1995 | Count Special Quadruplets | Java | $\text{\color{TealBlue}Easy}$ | Array, Enumeration | Solution Using Hash Table |
| 2006 | Count Number of Pairs With Absolute Difference K | Java with Brute Force, Counting or Hash Table | $\text{\color{TealBlue}Easy}$ | Array, Counting, Hash Table | |
| 2007 | Find Original Array From Doubled Array | Java with Hash Table, Queue or Counting Array | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Hash Table, Sorting | |
| 2023 | Number of Pairs of Strings With Concatenation Equal to Target | Java | $\text{\color{Dandelion}Medium}$ | Array, String | |
| 2028 | Find Missing Observations | Java | $\text{\color{Dandelion}Medium}$ | Array, Math, Simulation | |
| 2131 | Longest Palindrome by Concatenating Two Letter Words | Java with Counting or Hash Table | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy, Hash Table, String | |
| 2133 | Check if Every Row and Column Contains All Numbers | Java without or with Hash Table | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Matrix | |
| 2136 | Earliest Possible Day of Full Bloom | Java | $\text{\color{Red}Hard}$ | Array, Greedy, Sorting | |
| 2176 | Count Equal and Divisible Pairs in an Array | Java | $\text{\color{TealBlue}Easy}$ | Array | |
| 2244 | Minimum Rounds to Complete All Tasks | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy, Hash Table | |
| 2279 | Maximum Bags With Full Capacity of Rocks | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Sorting | |
| 2352 | Equal Row and Column Pairs | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Matrix, Simulation | |
| 2389 | Longest Subsequence With Limited Sum | Java | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Greedy, Prefix Sum, Sorting | |
| 2395 | Find Subarrays With Equal Sum | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table | |
| 2399 | Check Distances Between Same Letters | Java without or with Hash Table | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, String | |
| 2438 | Range Product Queries of Powers | Java | $\text{\color{Dandelion}Medium}$ | Array, Bit Manipulation, Prefix Sum | |
| 2452 | Words Within Two Edits of Dictionary | Java | $\text{\color{Dandelion}Medium}$ | Array, String | |
| 2453 | Destroy Sequential Targets | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table | |
| 2454 | Next Greater Element IV | Java | $\text{\color{Red}Hard}$ | Array, Monotonic Stack, Stack |
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Backtracking
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 37 | Sudoku Solver | Java | $\text{\color{Red}Hard}$ | Array, Backtracking, Matrix | |
| 46 | Permutations | Java | $\text{\color{Dandelion}Medium}$ | Array, Backtracking | Solution Using Iteration or Recursion |
| 79 | Word Search | Java | $\text{\color{Dandelion}Medium}$ | Array, Backtracking, Matrix | |
| 113 | Path Sum II | Java with Backtracking and Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Backtracking, Binary Tree, Depth-First Search, Tree | |
| 257 | Binary Tree Paths | Java with Backtracking and Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Backtracking, Binary Tree, Depth-First Search, String, Tree | |
| 797 | All Paths From Source to Target | Java | $\text{\color{Dandelion}Medium}$ | Backtracking, Breadth-First Search, Depth-First Search, Graph | Solution Using Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 967 | Numbers With Same Consecutive Differences | Java | $\text{\color{Dandelion}Medium}$ | Backtracking, Breadth-First Search | Solution Using Breadth-First Search |
| 1239 | Maximum Length of a Concatenated String with Unique Characters | Java | $\text{\color{Dandelion}Medium}$ | Array, Backtracking, Bit Manipulation, String | Solution Using Bit Manipulation |
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Binary Search
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 102 | Binary Tree Level Order Traversal | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Breadth-First Search, Tree | |
| 103 | Binary Tree Zigzag Level Order Traversal | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Breadth-First Search, Tree | |
| 107 | Binary Tree Level Order Traversal II | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Breadth-First Search, Tree | |
| 144 | Binary Tree Preorder Traversal | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search, Depth-First Search, Stack, Tree | |
| 145 | Binary Tree Postorder Traversal | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search, Depth-First Search, Stack, Tree | |
| 167 | Two Sum II - Input Array is Sorted | Java | $\text{\color{Dandelion}Medium}$ | Array, Binary Search, Two Pointers | Solution Using Two Pointers |
| 222 | Count Complete Tree Nodes | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Binary Tree, Depth-First Search, Tree | |
| 275 | H-Index II | Java | $\text{\color{Dandelion}Medium}$ | Array, Binary Search | |
| 374 | Guess Number Higher or Lower | Java | $\text{\color{TealBlue}Easy}$ | Binary Search, Interactive | |
| 744 | Find Smallest Letter Greater Than Target | Java | $\text{\color{TealBlue}Easy}$ | Array, Binary Search | Solution Using Linear Search |
| 1337 | The K Weakest Rows in a Matrix | Java with Binary Search, Heap (Priority Queue) & Binary Search or Sorting & Binary Search | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Heap (Priority Queue), Matrix, Sorting | Solution Using Linear Search |
| 1346 | Check If N and Its Double Exist | Java with Binary Search & Sorting | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Hash Table, Sorting, Two Pointers | Solution Using Hash Table or Two Pointers |
| 1351 | Count Negative Numbers in a Sorted Matrix | Java | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Matrix | Solution Using Linear Search |
| 2389 | Longest Subsequence With Limited Sum | Java | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Greedy, Prefix Sum, Sorting |
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Binary Search Tree
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 98 | Validate Binary Search Tree | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Search Tree, Binary Tree, Depth-First Search, Tree | |
| 653 | Two Sum IV - Input is a BST | Java with Breadth-First Search (with Hash Table), Breadth-First Search (without Hash Table), Depth-First Search (Iterative), Depth-First Search (Recursive), Two Pointers (with Iterative Inorder Traversal) or Two Pointers (with Recursive Inorder Traversal) | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Hash Table, Tree, Two Pointers | |
| 783 | Minimum Distance Between BST Nodes | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Tree |
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Binary Tree
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 94 | Binary Tree Inorder Traversal | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Depth-First Search, Stack, Tree | |
| 98 | Validate Binary Search Tree | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Search Tree, Binary Tree, Depth-First Search, Tree | |
| 100 | Same Tree | Java with Breadth-First Search or Depth-First Search | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 104 | Maximum Depth of Binary Tree | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 110 | Balanced Binary Tree | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Depth-First Search, Tree | |
| 111 | Minimum Depth of Binary Tree | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 112 | Path Sum | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 113 | Path Sum II | Java with Backtracking and Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Backtracking, Binary Tree, Depth-First Search, Tree | |
| 114 | Flatten Binary Tree to Linked List | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Linked List, Stack, Tree | |
| 129 | Sum Root to Leaf Numbers | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Tree | |
| 222 | Count Complete Tree Nodes | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Binary Tree, Depth-First Search, Tree | |
| 226 | Invert Binary Tree | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 257 | Binary Tree Paths | Java with Backtracking and Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Backtracking, Binary Tree, Depth-First Search, String, Tree | |
| 404 | Sum of Left Leaves | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 437 | Path Sum III | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Tree | |
| 653 | Two Sum IV - Input is a BST | Java with Breadth-First Search (with Hash Table), Breadth-First Search (without Hash Table), Depth-First Search (Iterative), Depth-First Search (Recursive), Two Pointers (with Iterative Inorder Traversal) or Two Pointers (with Recursive Inorder Traversal) | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Hash Table, Tree, Two Pointers | |
| 783 | Minimum Distance Between BST Nodes | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 988 | Smallest String Starting From Leaf | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, String, Tree | |
| 1026 | Maximum Difference Between Node and Ancestor | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Tree | |
| 1457 | Pseudo-Palindromic Paths in a Binary Tree | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Bit Manipulation, Breadth-First Search, Depth-First Search, Tree |
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Bit Manipulation
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 29 | Divide Two Integers | Java | $\text{\color{Dandelion}Medium}$ | Bit Manipulation, Math | |
| 136 | Single Number | Java | $\text{\color{TealBlue}Easy}$ | Array, Bit Manipulation | Bonus Solution Using Stream Reduce |
| 371 | Sum of Two Integers | Java | $\text{\color{Dandelion}Medium}$ | Bit Manipulation, Math | |
| 393 | UTF-8 Validation | Java | $\text{\color{Dandelion}Medium}$ | Array, Bit Manipulation | Solution without using Bit Manipulation |
| 645 | Set Mismatch | Java | $\text{\color{TealBlue}Easy}$ | Array, Bit Manipulation, Hash Table, Sorting | Solution Using Hash Table or Sorting |
| 1239 | Maximum Length of a Concatenated String with Unique Characters | Java | $\text{\color{Dandelion}Medium}$ | Array, Backtracking, Bit Manipulation, String | Solution Using Backtracking |
| 1318 | Minimum Flips to Make a OR b Equal to c | Java | $\text{\color{Dandelion}Medium}$ | Bit Manipulation | |
| 1342 | Number of Steps to Reduce a Number to Zero | Java | $\text{\color{TealBlue}Easy}$ | Bit Manipulation, Math | Solution Using Math |
| 1457 | Pseudo-Palindromic Paths in a Binary Tree | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Bit Manipulation, Breadth-First Search, Depth-First Search, Tree | |
| 1486 | XOR Operation in an Array | Java | $\text{\color{TealBlue}Easy}$ | Bit Manipulation, Math | |
| 1680 | Concatenation of Consecutive Binary Numbers | Java | $\text{\color{Dandelion}Medium}$ | Bit Manipulation, Math, Simulation | Solution Using Math |
| 2220 | Minimum Bit Flips to Convert Number | Java | $\text{\color{TealBlue}Easy}$ | Bit Manipulation | |
| 2438 | Range Product Queries of Powers | Java | $\text{\color{Dandelion}Medium}$ | Array, Bit Manipulation, Prefix Sum |
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Brainteaser
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 1033 | Moving Stones Until Consecutive | Java | $\text{\color{Dandelion}Medium}$ | Brainteaser, Math |
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Breadth-First Search
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 100 | Same Tree | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Depth-First Search |
| 102 | Binary Tree Level Order Traversal | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Breadth-First Search, Tree | |
| 103 | Binary Tree Zigzag Level Order Traversal | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Breadth-First Search, Tree | |
| 104 | Maximum Depth of Binary Tree | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 107 | Binary Tree Level Order Traversal II | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Breadth-First Search, Tree | |
| 111 | Minimum Depth of Binary Tree | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 112 | Path Sum | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 130 | Surrounded Regions | Java | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Depth-First Search, Matrix, Union Find | Solution Using Depth-First Search or Union Find |
| 200 | Number of Islands | Java | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Depth-First Search, Matrix, Union Find | Solution Using Depth-First Search or Union Find |
| 226 | Invert Binary Tree | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 404 | Sum of Left Leaves | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 429 | N-ary Tree Level Order Traversal | Java | $\text{\color{Dandelion}Medium}$ | Breadth-First Search, Tree | |
| 559 | Maximum Depth of Binary Tree | Java | $\text{\color{TealBlue}Easy}$ | Breadth-First Search, Depth-First Search, Tree | Solution Using Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 653 | Two Sum IV - Input is a BST | Java with or without Hash Table | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Hash Table, Tree, Two Pointers | Solution Using Depth-First Search (Iterative), Depth-First Search (Recursive), Two Pointers (with Iterative Inorder Traversal) or Two Pointers (with Recursive Inorder Traversal) |
| 783 | Minimum Distance Between BST Nodes | Java | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 797 | All Paths From Source to Target | Java | $\text{\color{Dandelion}Medium}$ | Backtracking, Breadth-First Search, Depth-First Search, Graph | Solution Using Depth-First Search (Backtracking), Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 967 | Numbers With Same Consecutive Differences | Java | $\text{\color{Dandelion}Medium}$ | Backtracking, Breadth-First Search | Solution Using Backtracking |
| 1457 | Pseudo-Palindromic Paths in a Binary Tree | Java | $\text{\color{Dandelion}Medium}$ | Binary Tree, Bit Manipulation, Breadth-First Search, Depth-First Search, Tree | Solution Using Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 1926 | Nearest Exit from Entrance in Maze | Java | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Matrix | |
| 1971 | Find if Path Exists in Graph | Java | $\text{\color{TealBlue}Easy}$ | Breadth-First Search, Depth-First Search, Graph, Union Find | Solution Using Depth-First Search (Iterative), Depth-First Search (Recursive) or Union Find |
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Bucket Sort
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 220 | Contains Duplicate III | Java with Sliding Window & Bucket Sort | $\text{\color{Red}Hard}$ | Array, Bucket Sort, Ordered Set, Sliding Window, Sorting | Solution Using Sliding Window & Ordered Set or Sorting |
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Counting
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 169 | Majority Element | Java with Counting & Divide and Conquer or Counting & Hash Table | $\text{\color{TealBlue}Easy}$ | Array, Counting, Divide and Conquer, Hash Table, Sorting | Solution Using Boyer-Moore Majority Voting Algorithm or Sorting |
| 229 | Majority Element II | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Sorting | Solution Using Boyer-Moore Majority Voting Algorithm or Sorting |
| 383 | Ransom Note | Java | $\text{\color{TealBlue}Easy}$ | Counting, Hash Table, String | Solution Using Hash Table |
| 923 | 3Sum With Multiplicity | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Sorting, Two Pointers | Solution Using Hash Table or Sorting & Two Pointers |
| 1497 | Check If Array Pairs Are Divisible by k | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table | Solution Using Hash Table |
| 1603 | Design Parking System | Java | $\text{\color{TealBlue}Easy}$ | Counting, Design, Simulation | |
| 1704 | Determine if String Halves Are Alike | Java | $\text{\color{TealBlue}Easy}$ | Counting, String | |
| 1775 | Equal Sum Arrays With Minimum Number of Operations | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy | |
| 1814 | Count Nice Pairs in an Array | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Math | |
| 2006 | Count Number of Pairs With Absolute Difference K | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting, Hash Table | Solution Using Brute Force Approach or Hash Table |
| 2131 | Longest Palindrome by Concatenating Two Letter Words | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy, Hash Table, String | Solution Using Hash Table |
| 2244 | Minimum Rounds to Complete All Tasks | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy, Hash Table | |
| 2351 | First Letter to Appear Twice | Java | $\text{\color{TealBlue}Easy}$ | Counting, Hash Table, String | Solution Using Hash Table |
| 2453 | Destroy Sequential Targets | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table |
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Counting Sort
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 274 | H-Index | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Sorting | Solution Using Sorting |
| 561 | Array Partition | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Greedy, Sorting | Solution Using Greedy & Sorting |
| 1051 | Height Checker | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Sorting | Solution Using Sorting |
| 1122 | Relative Sort Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Hash Table, Sorting | Solution Using Hash Table |
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Data Stream
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 295 | Find Median from Data Stream | Java | $\text{\color{Red}Hard}$ | Data Stream, Design, Heap (Priority Queue), Sorting, Two Pointers |
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Depth-First Search
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 94 | Binary Tree Inorder Traversal | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Depth-First Search, Stack, Tree | |
| 98 | Validate Binary Search Tree | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Search Tree, Binary Tree, Depth-First Search, Tree | |
| 100 | Same Tree | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Breadth-First Search |
| 104 | Maximum Depth of Binary Tree | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Breadth-First Search |
| 110 | Balanced Binary Tree | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Depth-First Search, Tree | |
| 111 | Minimum Depth of Binary Tree | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Breadth-First Search |
| 112 | Path Sum | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Breadth-First Search |
| 113 | Path Sum II | Java with Backtracking and Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Backtracking, Binary Tree, Depth-First Search, Tree | |
| 114 | Flatten Binary Tree to Linked List | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Linked List, Stack, Tree | |
| 129 | Sum Root to Leaf Numbers | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Tree | |
| 130 | Surrounded Regions | Java | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Depth-First Search, Matrix, Union Find | Solution Using Breadth-First Search or Union Find |
| 144 | Binary Tree Preorder Traversal | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search, Depth-First Search, Stack, Tree | |
| 145 | Binary Tree Postorder Traversal | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search, Depth-First Search, Stack, Tree | |
| 200 | Number of Islands | Java | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Depth-First Search, Matrix, Union Find | Solution Using Breadth-First Search or Union Find |
| 222 | Count Complete Tree Nodes | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Binary Tree, Depth-First Search, Tree | |
| 226 | Invert Binary Tree | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Breadth-First Search |
| 257 | Binary Tree Paths | Java with Backtracking and Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Backtracking, Binary Tree, Depth-First Search, String, Tree | |
| 404 | Sum of Left Leaves | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Breadth-First Search |
| 437 | Path Sum III | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Tree | |
| 559 | Maximum Depth of Binary Tree | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Breadth-First Search, Depth-First Search, Tree | Solution Using Breadth-First Search |
| 653 | Two Sum IV - Input is a BST | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Hash Table, Tree, Two Pointers | Solution Using Breadth-First Search (with Hash Table), Breadth-First Search (without Hash Table), Two Pointers (with Iterative Inorder Traversal) or Two Pointers (with Recursive Inorder Traversal) |
| 783 | Minimum Distance Between BST Nodes | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Tree | Solution Using Breadth-First Search |
| 797 | All Paths From Source to Target | Java with Depth-First Search (Backtracking), Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Backtracking, Breadth-First Search, Depth-First Search, Graph | Solution Using Breadth-First Search |
| 988 | Smallest String Starting From Leaf | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, String, Tree | |
| 1026 | Maximum Difference Between Node and Ancestor | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Tree | |
| 1457 | Pseudo-Palindromic Paths in a Binary Tree | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Bit Manipulation, Breadth-First Search, Depth-First Search, Tree | Solution Using Breadth-First Search |
| 1971 | Find if Path Exists in Graph | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Breadth-First Search, Depth-First Search, Graph, Union Find | Solution Using Breadth-First Search or Union Find |
| 2359 | Find Closest Node to Given Two Nodes | Java | $\text{\color{Dandelion}Medium}$ | Depth-First Search, Graph |
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Design
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 225 | Implement Stack using Queues | Java | $\text{\color{TealBlue}Easy}$ | Design, Queue, Stack | |
| 232 | Implement Queue using Stacks | Java | $\text{\color{TealBlue}Easy}$ | Design, Queue, Stack | |
| 295 | Find Median from Data Stream | Java | $\text{\color{Red}Hard}$ | Data Stream, Design, Heap (Priority Queue), Sorting, Two Pointers | |
| 707 | Design Linked List | Java with Singly Linked List or Doubly Linked List | $\text{\color{Dandelion}Medium}$ | Design, Linked List | |
| 1603 | Design Parking System | Java | $\text{\color{TealBlue}Easy}$ | Counting, Design, Simulation | |
| 1865 | Finding Pairs With a Certain Sum | Java | $\text{\color{Dandelion}Medium}$ | Array, Design, Hash Table |
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Divide and Conquer
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 169 | Majority Element | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting, Divide and Conquer, Hash Table, Sorting | Solution Using Boyer-Moore Majority Voting Algorithm, Counting & Hash Table or Sorting |
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Dynamic Programming
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 5 | Longest Palindromic Substring | Java | $\text{\color{Dandelion}Medium}$ | Dynamic Programming, String | Solution Using Two Pointers with Approach 1 or Approach 2 |
| 45 | Jump Game II | Java with Dynamic Programming - Memoization or Tabulation | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Greedy | Solution Using Greedy |
| 55 | Jump Game | Java | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Greedy | Solution Using Greedy |
| 70 | Climbing Stairs | Java with Dynamic Programming - Tabulation or Memoization | $\text{\color{TealBlue}Easy}$ | Dynamic Programming, Math, Memoization | |
| 121 | Best Time to Buy and Sell Stock | Java | $\text{\color{TealBlue}Easy}$ | Array, Dynamic Programming | Solution without Using Dynamic Programming |
| 152 | Maximum Product Subarray | Java | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming | Solution Using Array |
| 264 | Ugly Number II | Java | $\text{\color{Dandelion}Medium}$ | Dynamic Programming, Hash Table, Heap (Priority Queue), Math | Solution Using Heap (Priority Queue) |
| 368 | Largest Divisible Subset | Java | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Math, Sorting | |
| 509 | Fibonacci Number | Java with Dynamic Programming - Tabulation or Memoization | $\text{\color{TealBlue}Easy}$ | Dynamic Programming, Math, Memoization, Recursion | |
| 746 | Min Cost Climbing Stairs | Java with Dynamic Programming - Tabulation or Memoization | $\text{\color{TealBlue}Easy}$ | Array, Dynamic Programming | |
| 1137 | N-th Tribonacci Number | Java with Dynamic Programming Iteratively or Recursively (Memoization) | $\text{\color{TealBlue}Easy}$ | Dynamic Programming, Math, Memoization | |
| 1155 | Number of Dice Rolls With Target Sum | Java with Dynamic Programming using Memoization or Tabulation | $\text{\color{Dandelion}Medium}$ | Dynamic Programming | |
| 1578 | Minimum Time to Make Rope Colorful | Java | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Greedy, String | Solution Using Greedy |
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Enumeration
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 1534 | Count Good Triplets | Java | $\text{\color{TealBlue}Easy}$ | Array, Enumeration | |
| 1995 | Count Special Quadruplets | Java | $\text{\color{TealBlue}Easy}$ | Array, Enumeration | Solution Using Hash Table |
| 2240 | Number of Ways to Buy Pens and Pencils | Java | $\text{\color{Dandelion}Medium}$ | Enumeration, Math | |
| 2437 | Number of Valid Clock Times | Java | $\text{\color{TealBlue}Easy}$ | Enumeration, String |
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Geometry
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 223 | Rectangle Area | Java | $\text{\color{Dandelion}Medium}$ | Geometry, Math | |
| 593 | Valid Square | Java | $\text{\color{Dandelion}Medium}$ | Geometry, Math | |
| 812 | Largest Triangle Area | Java | $\text{\color{TealBlue}Easy}$ | Array, Geometry, Math | |
| 836 | Rectangle Overlap | Java | $\text{\color{TealBlue}Easy}$ | Geometry, Math | |
| 1037 | Valid Boomerang | Java | $\text{\color{TealBlue}Easy}$ | Array, Geometry, Math | |
| 1232 | Check If It Is a Straight Line | Java | $\text{\color{TealBlue}Easy}$ | Array, Geometry, Math |
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Graph
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 797 | All Paths From Source to Target | Java with Breadth-First Search, Depth-First Search (Backtracking), Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Backtracking, Breadth-First Search, Depth-First Search, Graph | |
| 1971 | Find if Path Exists in Graph | Java with Breadth-First Search, Depth-First Search (Iterative), Depth-First Search (Recursive) or Union Find | $\text{\color{TealBlue}Easy}$ | Breadth-First Search, Depth-First Search, Graph, Union Find | |
| 2359 | Find Closest Node to Given Two Nodes | Java | $\text{\color{Dandelion}Medium}$ | Depth-First Search, Graph |
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Greedy
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 45 | Jump Game II | Java with Greedy | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Greedy | Solution Using Dynamic Programming (Memoization) or Dynamic Programming (Tabulation) |
| 55 | Jump Game | Java with Greedy | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Greedy | Solution Using Dynamic Programming |
| 134 | Gas Station | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy | |
| 334 | Increasing Triplet Subsequence | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy | |
| 561 | Array Partition | Java with Greedy & Counting Sort or Greedy & Sorting | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Greedy, Sorting | |
| 948 | Bag of Tokens | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Sorting, Two Pointers | |
| 976 | Largest Perimeter Triangle | Java | $\text{\color{TealBlue}Easy}$ | Array, Greedy, Math, Sorting | |
| 1323 | Maximum 69 Number | Java with Math or String | $\text{\color{TealBlue}Easy}$ | Greedy, Math | |
| 1328 | Break a Palindrome | Java | $\text{\color{Dandelion}Medium}$ | Greedy, String | |
| 1578 | Minimum Time to Make Rope Colorful | Java | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Greedy, String | Solution Using Dynamic Programming |
| 1775 | Equal Sum Arrays With Minimum Number of Operations | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy | |
| 1833 | Maximum Ice Cream Bars | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Sorting | |
| 2007 | Find Original Array From Doubled Array | Java with Hash Table, Queue or Counting Array | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Hash Table, Sorting | |
| 2131 | Longest Palindrome by Concatenating Two Letter Words | Java with Counting or Hash Table | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy, Hash Table, String | |
| 2136 | Earliest Possible Day of Full Bloom | Java | $\text{\color{Red}Hard}$ | Array, Greedy, Sorting | |
| 2244 | Minimum Rounds to Complete All Tasks | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy, Hash Table | |
| 2279 | Maximum Bags With Full Capacity of Rocks | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Sorting | |
| 2389 | Longest Subsequence With Limited Sum | Java | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Greedy, Prefix Sum, Sorting |
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Hash Table
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 1 | Two Sum | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table | |
| 3 | Longest Substring Without Repeating Characters | Java | $\text{\color{Dandelion}Medium}$ | Hash Table, Sliding Window, String | Solution without Using Hash Table |
| 12 | Integer to Roman | Java | $\text{\color{Dandelion}Medium}$ | Hash Table, Math, String | Solution without Hash Table |
| 13 | Roman to Integer | Java | $\text{\color{TealBlue}Easy}$ | Hash Table, Math, String | Solution without Hash Table |
| 36 | Valid Sudoku | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Matrix | Solution without Hash Table |
| 49 | Group Anagrams | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting, String | |
| 73 | Set Matrix Zeroes | Java with Array, Hash Table or In-Place | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Matrix | |
| 169 | Majority Element | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting, Divide and Conquer, Hash Table, Sorting | Solution Using Boyer-Moore Majority Voting Algorithm, Counting & Divide and Conquer or Sorting |
| 205 | Isomorphic Strings | Java | $\text{\color{TealBlue}Easy}$ | Hash Table, String | |
| 217 | Contains Duplicate | Java with Hash Map or Hash Set | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Sorting | Solution Using Sorting |
| 219 | Contains Duplicate II | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Sliding Window | Solution Using Sliding Window |
| 229 | Majority Element II | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Sorting | Solution Using Boyer-Moore Majority Voting Algorithm or Sorting |
| 264 | Ugly Number II | Java with Dynamic Programming or Heap (Priority Queue) | $\text{\color{Dandelion}Medium}$ | Dynamic Programming, Hash Table, Heap (Priority Queue), Math | |
| 290 | Word Pattern | Java | $\text{\color{TealBlue}Easy}$ | Hash Table, String | |
| 383 | Ransom Note | Java | $\text{\color{TealBlue}Easy}$ | Counting, Hash Table, String | Solution Using Counting Array |
| 438 | Find All Anagrams in a String | Java | $\text{\color{Dandelion}Medium}$ | Hash Table, Sliding Window, String | |
| 448 | Find All Numbers Disappeared in an Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table | Solution without Hash Table |
| 496 | Next Greater Element I | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Monotonic Stack, Stack | |
| 523 | Continuous Subarray Sum | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Math, Prefix Sum | |
| 560 | Subarray Sum Equals K | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Prefix Sum | |
| 567 | Permutation in String | Java | $\text{\color{Dandelion}Medium}$ | Hash Table, Sliding Window, String, Two Pointers | |
| 609 | Find Duplicate File in System | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, String | |
| 645 | Set Mismatch | Java | $\text{\color{TealBlue}Easy}$ | Array, Bit Manipulation, Hash Table, Sorting | Solution Using Bit Manipulation or Sorting |
| 653 | Two Sum IV - Input is a BST | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Hash Table, Tree, Two Pointers | Solution Using Breadth-First Search (without Hash Table), Two Pointers (with Iterative Inorder Traversal) or Two Pointers (with Recursive Inorder Traversal) |
| 904 | Fruit Into Baskets | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sliding Window | |
| 923 | 3Sum With Multiplicity | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Sorting, Two Pointers | Solution Using Counting or Sorting & Two Pointers |
| 929 | Unique Email Addresses | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, String | |
| 953 | Verifying an Alien Dictionary | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, String | |
| 974 | Subarray Sums Divisible by K | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Prefix Sum | Solution Using Counting |
| 1122 | Relative Sort Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Hash Table, Sorting | Solution Using Counting Sort |
| 1207 | Unique Number of Occurrences | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table | Solution Using Counting & Sorting |
| 1346 | Check If N and Its Double Exist | Java with Hash Table | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Hash Table, Sorting, Two Pointers | Solution Using Binary Search & Sorting or Two Pointers |
| 1497 | Check If Array Pairs Are Divisible by k | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table | Solution Using Counting |
| 1636 | Sort Array by Increasing Frequency | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Sorting | |
| 1657 | Determine if Two Strings Are Close | Java with Hash Table & Sorting | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting | Solution Using only Sorting |
| 1679 | Max Number of K-Sum Pairs | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting, Two Pointers | Solution Using Sorting & Two Pointers |
| 1711 | Count Good Meals | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table | |
| 1814 | Count Nice Pairs in an Array | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Math | |
| 1832 | Check if the Sentence is Pangram | Java | $\text{\color{TealBlue}Easy}$ | Hash Table, String | Solution Using Bit Manipulation , Counting and Without Hash Table |
| 1865 | Finding Pairs With a Certain Sum | Java | $\text{\color{Dandelion}Medium}$ | Array, Design, Hash Table | |
| 1935 | Maximum Number of Words You Can Type | Java | $\text{\color{TealBlue}Easy}$ | Hash Table, String | |
| 2006 | Count Number of Pairs With Absolute Difference K | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting, Hash Table | Solution Using Brute Force, Counting |
| 2007 | Find Original Array From Doubled Array | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Hash Table, Sorting | Solution Using Queue or Counting Array |
| 2131 | Longest Palindrome by Concatenating Two Letter Words | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy, Hash Table, String | Solution Using Counting |
| 2133 | Check if Every Row and Column Contains All Numbers | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Matrix | Solution Without Hash Table |
| 2244 | Minimum Rounds to Complete All Tasks | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy, Hash Table | |
| 2351 | First Letter to Appear Twice | Java | $\text{\color{TealBlue}Easy}$ | Counting, Hash Table, String | Solution Using Counting |
| 2352 | Equal Row and Column Pairs | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Matrix, Simulation | |
| 2395 | Find Subarrays With Equal Sum | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table | |
| 2399 | Check Distances Between Same Letters | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, String | Solution Without Hash Table |
| 2451 | Odd String Difference | Java | $\text{\color{TealBlue}Easy}$ | Hash Table, Math, String | Solution Without Hash Table |
| 2453 | Destroy Sequential Targets | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table |
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Heap (Priority Queue)
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 264 | Ugly Number II | Java | $\text{\color{Dandelion}Medium}$ | Dynamic Programming, Hash Table, Heap (Priority Queue), Math | Solution Using Dynamic Programming |
| 295 | Find Median from Data Stream | Java | $\text{\color{Red}Hard}$ | Data Stream, Design, Heap (Priority Queue), Sorting, Two Pointers | |
| 1337 | The K Weakest Rows in a Matrix | Java with Heap (Priority Queue) & Binary Search | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Heap (Priority Queue), Matrix, Sorting | Solution Using Linear Search, Binary Search, Sorting & Binary Search |
| 1834 | Single-Threaded CPU | Java | $\text{\color{Dandelion}Medium}$ | Array, Heap (Priority Queue), Sorting | |
| 1962 | Remove Stones to Minimize the Total | Java | $\text{\color{Dandelion}Medium}$ | Array, Heap (Priority Queue) |
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Interactive
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 374 | Guess Number Higher or Lower | Java | $\text{\color{TealBlue}Easy}$ | Binary Search, Interactive |
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Linked List
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 19 | Remove Nth Node From End of List | Java with One Pass or Two Passes | $\text{\color{Dandelion}Medium}$ | Linked List, Two Pointers | |
| 24 | Swap Nodes in Pairs | Java with Iteration or Recursion | $\text{\color{Dandelion}Medium}$ | Linked List, Recursion | |
| 92 | Reverse Linked List II | Java | $\text{\color{Dandelion}Medium}$ | Linked List | |
| 114 | Flatten Binary Tree to Linked List | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Linked List, Stack, Tree | |
| 206 | Reverse Linked List | Java with Array List, Reverse Nodes Iteratively or Recursively | $\text{\color{TealBlue}Easy}$ | Linked List, Recursion | |
| 707 | Design Linked List | Java with Singly Linked List or Doubly Linked List | $\text{\color{Dandelion}Medium}$ | Design, Linked List | |
| 876 | Middle of the Linked List | Java | $\text{\color{TealBlue}Easy}$ | Linked List, Two Pointers | |
| 1019 | Next Greater Node In Linked List | Java | $\text{\color{Dandelion}Medium}$ | Array, Linked List, Monotonic Stack, Stack | |
| 2095 | Delete the Middle Node of a Linked List | Java | $\text{\color{Dandelion}Medium}$ | Linked List, Two Pointers | |
| 2130 | Maximum Twin Sum of a Linked List | Java with Two Pointers or Two Pointers & Stack | $\text{\color{Dandelion}Medium}$ | Linked List, Stack, Two Pointers |
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Math
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 12 | Integer to Roman | Java with or without Hash Table | $\text{\color{Dandelion}Medium}$ | Hash Table, Math, String | |
| 13 | Roman to Integer | Java with or without Hash Table | $\text{\color{TealBlue}Easy}$ | Hash Table, Math, String | |
| 29 | Divide Two Integers | Java | $\text{\color{Dandelion}Medium}$ | Bit Manipulation, Math | |
| 70 | Climbing Stairs | Java with Dynamic Programming - Tabulation or Memoization | $\text{\color{TealBlue}Easy}$ | Dynamic Programming, Math, Memoization | |
| 223 | Rectangle Area | Java | $\text{\color{Dandelion}Medium}$ | Geometry, Math | |
| 263 | Ugly Number | Java | $\text{\color{TealBlue}Easy}$ | Math | |
| 264 | Ugly Number II | Java with Dynamic Programming or Heap (Priority Queue) | $\text{\color{Dandelion}Medium}$ | Dynamic Programming, Hash Table, Heap (Priority Queue), Math | |
| 368 | Largest Divisible Subset | Java | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Math, Sorting | |
| 371 | Sum of Two Integers | Java | $\text{\color{Dandelion}Medium}$ | Bit Manipulation, Math | |
| 412 | Fizz Buzz | Java | $\text{\color{TealBlue}Easy}$ | Math, Simulation, String | |
| 492 | Construct the Rectangle | Java | $\text{\color{TealBlue}Easy}$ | Math | |
| 509 | Fibonacci Number | Java with Dynamic Programming - Tabulation or Memoization | $\text{\color{TealBlue}Easy}$ | Dynamic Programming, Math, Memoization, Recursion | |
| 523 | Continuous Subarray Sum | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Math, Prefix Sum | |
| 556 | Next Greater Element III | Java | $\text{\color{Dandelion}Medium}$ | Math, String, Two Pointers | |
| 593 | Valid Square | Java | $\text{\color{Dandelion}Medium}$ | Geometry, Math | |
| 812 | Largest Triangle Area | Java | $\text{\color{TealBlue}Easy}$ | Array, Geometry, Math | |
| 836 | Rectangle Overlap | Java | $\text{\color{TealBlue}Easy}$ | Geometry, Math | |
| 976 | Largest Perimeter Triangle | Java | $\text{\color{TealBlue}Easy}$ | Array, Greedy, Math, Sorting | |
| 989 | Add to Array-Form of Integer | Java | $\text{\color{TealBlue}Easy}$ | Array, Math | |
| 1033 | Moving Stones Until Consecutive | Java | $\text{\color{Dandelion}Medium}$ | Brainteaser, Math | |
| 1037 | Valid Boomerang | Java | $\text{\color{TealBlue}Easy}$ | Array, Geometry, Math | |
| 1071 | Greatest Common Divisor of Strings | Java | $\text{\color{TealBlue}Easy}$ | Math, String | |
| 1103 | Distribute Candies to People | Java | $\text{\color{TealBlue}Easy}$ | Math, Simulation | |
| 1137 | N-th Tribonacci Number | Java with Dynamic Programming Iteratively or Recursively (Memoization) | $\text{\color{TealBlue}Easy}$ | Dynamic Programming, Math, Memoization | |
| 1154 | Day of the Year | Java | $\text{\color{TealBlue}Easy}$ | Math, String | |
| 1232 | Check If It Is a Straight Line | Java | $\text{\color{TealBlue}Easy}$ | Array, Geometry, Math | |
| 1323 | Maximum 69 Number | Java | $\text{\color{TealBlue}Easy}$ | Greedy, Math | Solution Using String |
| 1342 | Number of Steps to Reduce a Number to Zero | Java | $\text{\color{TealBlue}Easy}$ | Bit Manipulation, Math | Solution Using Bit Manipulation |
| 1486 | XOR Operation in an Array | Java | $\text{\color{TealBlue}Easy}$ | Bit Manipulation, Math | |
| 1523 | Count Odd Numbers in an Interval Range | Java | $\text{\color{TealBlue}Easy}$ | Math | |
| 1680 | Concatenation of Consecutive Binary Numbers | Java | $\text{\color{Dandelion}Medium}$ | Bit Manipulation, Math, Simulation | Solution Using Bit Manipulation |
| 1814 | Count Nice Pairs in an Array | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Math | |
| 1979 | Find Greatest Common Divisor of Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Math, Number Theory | |
| 2028 | Find Missing Observations | Java | $\text{\color{Dandelion}Medium}$ | Array, Math, Simulation | |
| 2169 | Count Operations to Obtain Zero | Java | $\text{\color{TealBlue}Easy}$ | Math, Simulation | |
| 2240 | Number of Ways to Buy Pens and Pencils | Java | $\text{\color{Dandelion}Medium}$ | Enumeration, Math | |
| 2413 | Smallest Even Multiple | Java | $\text{\color{TealBlue}Easy}$ | Math, Number Theory | |
| 2451 | Odd String Difference | Java without or with Hash Table | $\text{\color{TealBlue}Easy}$ | Hash Table, Math, String |
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Matrix
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 36 | Valid Sudoku | Java without or with Hash Table | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Matrix | |
| 37 | Sudoku Solver | Java | $\text{\color{Red}Hard}$ | Array, Backtracking, Matrix | |
| 73 | Set Matrix Zeroes | Java with Array, Hash Table or In-Place | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Matrix | |
| 79 | Word Search | Java | $\text{\color{Dandelion}Medium}$ | Array, Backtracking, Matrix | |
| 130 | Surrounded Regions | Java with Breadth-First Search, Depth-First Search or Union Find | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Depth-First Search, Matrix, Union Find | |
| 200 | Number of Islands | Java with Breadth-First Search, Depth-First Search or Union Find | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Depth-First Search, Matrix, Union Find | |
| 766 | Toeplitz Matrix | Java | $\text{\color{TealBlue}Easy}$ | Array, Matrix | Follow up: One Row at a Time and One Column at a Time |
| 835 | Image Overlap | Java with Bit Manipulation or Hash Table | $\text{\color{Dandelion}Medium}$ | Array, Matrix | |
| 1337 | The K Weakest Rows in a Matrix | Java with Linear Search, Binary Search, Heap (Priority Queue) or Sorting | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Heap (Priority Queue), Matrix, Sorting | |
| 1351 | Count Negative Numbers in a Sorted Matrix | Java with Linear Search or Binary Search | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Matrix | |
| 1672 | Richest Customer Wealth | Java | $\text{\color{TealBlue}Easy}$ | Array, Matrix | |
| 1926 | Nearest Exit from Entrance in Maze | Java | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Matrix | |
| 2133 | Check if Every Row and Column Contains All Numbers | Java without or with Hash Table | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Matrix | |
| 2352 | Equal Row and Column Pairs | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Matrix, Simulation |
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Memoization
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 70 | Climbing Stairs | Java with Dynamic Programming - Tabulation or Memoization | $\text{\color{TealBlue}Easy}$ | Dynamic Programming, Math, Memoization | |
| 509 | Fibonacci Number | Java with Dynamic Programming - Tabulation or Memoization | $\text{\color{TealBlue}Easy}$ | Dynamic Programming, Math, Memoization, Recursion | |
| 1137 | N-th Tribonacci Number | Java | $\text{\color{TealBlue}Easy}$ | Dynamic Programming, Math, Memoization | Solution Using Dynamic Programming (Iterative) |
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Monotonic Stack
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 496 | Next Greater Element I | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Monotonic Stack, Stack | |
| 503 | Next Greater Element II | Java | $\text{\color{Dandelion}Medium}$ | Array, Monotonic Stack, Stack | |
| 1019 | Next Greater Node In Linked List | Java | $\text{\color{Dandelion}Medium}$ | Array, Linked List, Monotonic Stack, Stack | |
| 2454 | Next Greater Element IV | Java | $\text{\color{Red}Hard}$ | Array, Monotonic Stack, Stack |
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Number Theory
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 1979 | Find Greatest Common Divisor of Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Math, Number Theory | |
| 2413 | Smallest Even Multiple | Java | $\text{\color{TealBlue}Easy}$ | Math, Number Theory |
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Ordered Set
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 220 | Contains Duplicate III | Java with Sliding Window & Ordered Set | $\text{\color{Red}Hard}$ | Array, Bucket Sort, Ordered Set, Sliding Window, Sorting | Solution Using Sliding Window & Bucket Sort or Sorting |
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Prefix Sum
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 238 | Product of Array Except Self | Java | $\text{\color{Dandelion}Medium}$ | Array, Prefix Sum | |
| 523 | Continuous Subarray Sum | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Math, Prefix Sum | |
| 560 | Subarray Sum Equals K | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Prefix Sum | |
| 974 | Subarray Sums Divisible by K | Java with Counting or Hash Table | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Prefix Sum | |
| 1480 | Running Sum of 1D Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Prefix Sum | |
| 1732 | Find the Highest Altitude | Java | $\text{\color{TealBlue}Easy}$ | Array, Prefix Sum | |
| 2389 | Longest Subsequence With Limited Sum | Java | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Greedy, Prefix Sum, Sorting | |
| 2438 | Range Product Queries of Powers | Java | $\text{\color{Dandelion}Medium}$ | Array, Bit Manipulation, Prefix Sum |
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Queue
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 225 | Implement Stack using Queues | Java | $\text{\color{TealBlue}Easy}$ | Design, Queue, Stack | |
| 232 | Implement Queue using Stacks | Java | $\text{\color{TealBlue}Easy}$ | Design, Queue, Stack |
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Recursion
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 24 | Swap Nodes in Pairs | Java | $\text{\color{Dandelion}Medium}$ | Linked List, Recursion | Solution Using Iteration |
| 206 | Reverse Linked List | Java | $\text{\color{TealBlue}Easy}$ | Linked List, Recursion | Solution Using Array List or Reverse Nodes Iteratively |
| 509 | Fibonacci Number | Java with Dynamic Programming - Tabulation or Memoization | $\text{\color{TealBlue}Easy}$ | Dynamic Programming, Math, Memoization, Recursion |
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Simulation
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 412 | Fizz Buzz | Java | $\text{\color{TealBlue}Easy}$ | Math, Simulation, String | |
| 985 | Sum of Even Numbers After Queries | Java | $\text{\color{Dandelion}Medium}$ | Array, Simulation | |
| 1103 | Distribute Candies to People | Java | $\text{\color{TealBlue}Easy}$ | Math, Simulation | |
| 1603 | Design Parking System | Java | $\text{\color{TealBlue}Easy}$ | Counting, Design, Simulation | |
| 1680 | Concatenation of Consecutive Binary Numbers | Java with Bit Manipulation or Math | $\text{\color{Dandelion}Medium}$ | Bit Manipulation, Math, Simulation | |
| 1920 | Build Array from Permutation | Java | $\text{\color{TealBlue}Easy}$ | Array, Simulation | |
| 2028 | Find Missing Observations | Java | $\text{\color{Dandelion}Medium}$ | Array, Math, Simulation | |
| 2169 | Count Operations to Obtain Zero | Java | $\text{\color{TealBlue}Easy}$ | Math, Simulation | |
| 2352 | Equal Row and Column Pairs | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Matrix, Simulation |
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Sliding Window
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 3 | Longest Substring Without Repeating Characters | Java with or without Hash Table | $\text{\color{Dandelion}Medium}$ | Hash Table, Sliding Window, String | |
| 219 | Contains Duplicate II | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Sliding Window | Solution Using Hash Table |
| 220 | Contains Duplicate III | Java with Sliding Window & Bucket Sort or Sliding Window & Ordered Set | $\text{\color{Red}Hard}$ | Array, Bucket Sort, Ordered Set, Sliding Window, Sorting | Solution Using Sorting |
| 438 | Find All Anagrams in a String | Java | $\text{\color{Dandelion}Medium}$ | Hash Table, Sliding Window, String | |
| 567 | Permutation in String | Java | $\text{\color{Dandelion}Medium}$ | Hash Table, Sliding Window, String, Two Pointers | |
| 713 | Subarray Product Less Than K | Java | $\text{\color{Dandelion}Medium}$ | Array, Sliding Window | |
| 904 | Fruit Into Baskets | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sliding Window |
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Sorting
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 15 | 3Sum | Java | $\text{\color{Dandelion}Medium}$ | Array, Sorting, Two Pointers | |
| 16 | 3Sum Closest | Java | $\text{\color{Dandelion}Medium}$ | Array, Sorting, Two Pointers | |
| 49 | Group Anagrams | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting, String | |
| 88 | Merge Sorted Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | Solution Using Two Pointers |
| 169 | Majority Element | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting, Divide and Conquer, Hash Table, Sorting | Solution Using Boyer-Moore Majority Voting Algorithm, Counting & Divide and Conquer or Counting & Hash Table |
| 217 | Contains Duplicate | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Sorting | Solution Using Hash Map or Hash Set |
| 220 | Contains Duplicate III | Java | $\text{\color{Red}Hard}$ | Array, Bucket Sort, Ordered Set, Sliding Window, Sorting | Solution Using Sliding Window & Bucket Sort or Sliding Window & Ordered Set |
| 229 | Majority Element II | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Sorting | Solution Using Boyer-Moore Majority Voting Algorithm or Counting & Hash Table |
| 274 | H-Index | Java with Counting Sort and Sorting | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Sorting | |
| 295 | Find Median from Data Stream | Java with Heap (Priority Queue) | $\text{\color{Red}Hard}$ | Data Stream, Design, Heap (Priority Queue), Sorting, Two Pointers | Use of Sorting & Two Pointers resulted in TLE (Time Limit Exceed) for large datasets. |
| 414 | Third Maximum Number | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting | Solution without Sorting or Using Hash Table & Priority Queue |
| 561 | Array Partition | Java with Greedy & Counting Sort or Greedy & Sorting | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Greedy, Sorting | |
| 645 | Set Mismatch | Java | $\text{\color{TealBlue}Easy}$ | Array, Bit Manipulation, Hash Table, Sorting | Solution Using Bit Manipulation or Hash Table |
| 905 | Sort Array By Parity | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | |
| 922 | Sort Array By Parity II | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | |
| 923 | 3Sum With Multiplicity | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Sorting, Two Pointers | Solution Using Counting Hash Table |
| 948 | Bag of Tokens | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Sorting, Two Pointers | |
| 976 | Largest Perimeter Triangle | Java | $\text{\color{TealBlue}Easy}$ | Array, Greedy, Math, Sorting | |
| 977 | Squares of a Sorted Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | Solution Using Two Pointers |
| 1051 | Height Checker | Java with Counting Sort or Sorting | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Sorting | |
| 1122 | Relative Sort Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Counting Sort, Hash Table, Sorting | Solution Using Hash Table |
| 1337 | The K Weakest Rows in a Matrix | Java with Sorting & Binary Search | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Heap (Priority Queue), Matrix, Sorting | Solution Using Linear Search, Binary Search or Heap (Priority Queue) & Binary Search |
| 1346 | Check If N and Its Double Exist | Java with Binary Search & Sorting | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Hash Table, Sorting, Two Pointers | Solution Using Hash Table or Two Pointers |
| 1636 | Sort Array by Increasing Frequency | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Sorting | |
| 1657 | Determine if Two Strings Are Close | Java with Sorting or Hash Table & Sorting | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting | |
| 1679 | Max Number of K-Sum Pairs | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting, Two Pointers | Solution Using Hash Table |
| 1833 | Maximum Ice Cream Bars | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Sorting | |
| 1834 | Single-Threaded CPU | Java | $\text{\color{Dandelion}Medium}$ | Array, Heap (Priority Queue), Sorting | |
| 2007 | Find Original Array From Doubled Array | Java with Hash Table or Queue | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Hash Table, Sorting | Solution Using Counting Array |
| 2136 | Earliest Possible Day of Full Bloom | Java | $\text{\color{Red}Hard}$ | Array, Greedy, Sorting | |
| 2279 | Maximum Bags With Full Capacity of Rocks | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Sorting | |
| 2389 | Longest Subsequence With Limited Sum | Java | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Greedy, Prefix Sum, Sorting |
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Stack
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 94 | Binary Tree Inorder Traversal | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Depth-First Search, Stack, Tree | Solution Using Depth-First Search (Recursive) |
| 114 | Flatten Binary Tree to Linked List | Java | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Linked List, Stack, Tree | Solution Using Depth-First Search (Recursive) |
| 144 | Binary Tree Preorder Traversal | Java | $\text{\color{TealBlue}Easy}$ | Binary Search, Depth-First Search, Stack, Tree | Solution Using Depth-First Search (Recursive) |
| 145 | Binary Tree Postorder Traversal | Java | $\text{\color{TealBlue}Easy}$ | Binary Search, Depth-First Search, Stack, Tree | Solution Using Depth-First Search (Recursive) |
| 225 | Implement Stack using Queues | Java | $\text{\color{TealBlue}Easy}$ | Design, Queue, Stack | |
| 232 | Implement Queue using Stacks | Java | $\text{\color{TealBlue}Easy}$ | Design, Queue, Stack | |
| 496 | Next Greater Element I | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, Monotonic Stack, Stack | |
| 503 | Next Greater Element II | Java | $\text{\color{Dandelion}Medium}$ | Array, Monotonic Stack, Stack | |
| 1019 | Next Greater Node In Linked List | Java | $\text{\color{Dandelion}Medium}$ | Array, Linked List, Monotonic Stack, Stack | |
| 1047 | Remove All Adjacent Duplicates In String | Java | $\text{\color{TealBlue}Easy}$ | Stack, String | Solution Using StringBuilder only |
| 1544 | Make The String Great | Java | $\text{\color{TealBlue}Easy}$ | Stack, String | |
| 2130 | Maximum Twin Sum of a Linked List | Java with Two Pointers & Stack | $\text{\color{Dandelion}Medium}$ | Linked List, Stack, Two Pointers | Solution Using only Two Pointers |
| 2454 | Next Greater Element IV | Java | $\text{\color{Red}Hard}$ | Array, Monotonic Stack, Stack |
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String
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 3 | Longest Substring Without Repeating Characters | Java with or without Hash Table | $\text{\color{Dandelion}Medium}$ | Hash Table, Sliding Window, String | |
| 5 | Longest Palindromic Substring | Java with Dynamic Programming, Two Pointers with Approach 1 or Approach 2 | $\text{\color{Dandelion}Medium}$ | Dynamic Programming, String | |
| 6 | Zigzag Conversion | Java | $\text{\color{Dandelion}Medium}$ | String | |
| 12 | Integer to Roman | Java with or without Hash Table | $\text{\color{Dandelion}Medium}$ | Hash Table, Math, String | |
| 13 | Roman to Integer | Java with or without Hash Table | $\text{\color{TealBlue}Easy}$ | Hash Table, Math, String | |
| 38 | Count and Say | Java with Iterative or Recursive Algorithms | $\text{\color{Dandelion}Medium}$ | String | |
| 49 | Group Anagrams | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting, String | |
| 151 | Reverse Words in a String | Java with StringBuilder or Collections Implementations | $\text{\color{Dandelion}Medium}$ | String, Two Pointers | Solution Using Two Pointers |
| 205 | Isomorphic Strings | Java | $\text{\color{TealBlue}Easy}$ | Hash Table, String | |
| 257 | Binary Tree Paths | Java with Backtracking and Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Backtracking, Binary Tree, Depth-First Search, String, Tree | |
| 290 | Word Pattern | Java | $\text{\color{TealBlue}Easy}$ | Hash Table, String | |
| 344 | Reverse String | Java | $\text{\color{TealBlue}Easy}$ | String, Two Pointers | |
| 345 | Reverse Vowels of a String | Java | $\text{\color{TealBlue}Easy}$ | String, Two Pointers | |
| 368 | Largest Divisible Subset | Java | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Math, Sorting | |
| 383 | Ransom Note | Java with Counting Array or Hash Table | $\text{\color{TealBlue}Easy}$ | Counting, Hash Table, String | |
| 412 | Fizz Buzz | Java | $\text{\color{TealBlue}Easy}$ | Math, Simulation, String | |
| 438 | Find All Anagrams in a String | Java | $\text{\color{Dandelion}Medium}$ | Hash Table, Sliding Window, String | |
| 520 | Detect Capital | Java | $\text{\color{TealBlue}Easy}$ | String | |
| 541 | Reverse String II | Java with StringBuilder or Two Pointers | $\text{\color{TealBlue}Easy}$ | String, Two Pointers | |
| 556 | Next Greater Element III | Java | $\text{\color{Dandelion}Medium}$ | Math, String, Two Pointers | |
| 557 | Reverse Words in a String III | Java with String Builder or Two Pointers | $\text{\color{TealBlue}Easy}$ | String, Two Pointers | |
| 567 | Permutation in String | Java | $\text{\color{Dandelion}Medium}$ | Hash Table, Sliding Window, String, Two Pointers | |
| 609 | Find Duplicate File in System | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, String | |
| 929 | Unique Email Addresses | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, String | |
| 944 | Delete Columns to Make Sorted | Java | $\text{\color{TealBlue}Easy}$ | Array, String | |
| 953 | Verifying an Alien Dictionary | Java | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, String | |
| 988 | Smallest String Starting From Leaf | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, String, Tree | |
| 1047 | Remove All Adjacent Duplicates In String | Java | $\text{\color{TealBlue}Easy}$ | Stack, String | Solution Using Stack |
| 1061 | Lexicographically Smallest Equivalent String | Java | $\text{\color{Dandelion}Medium}$ | String, Union Find | |
| 1071 | Greatest Common Divisor of Strings | Java | $\text{\color{TealBlue}Easy}$ | Math, String | |
| 1154 | Day of the Year | Java | $\text{\color{TealBlue}Easy}$ | Math, String | |
| 1239 | Maximum Length of a Concatenated String with Unique Characters | Java with Backtracking or Bit Manipulation | $\text{\color{Dandelion}Medium}$ | Array, Backtracking, Bit Manipulation, String | |
| 1328 | Break a Palindrome | Java | $\text{\color{Dandelion}Medium}$ | Greedy, String | |
| 1446 | Consecutive Characters | Java | $\text{\color{TealBlue}Easy}$ | String | |
| 1544 | Make The String Great | Java | $\text{\color{TealBlue}Easy}$ | Stack, String | |
| 1578 | Minimum Time to Make Rope Colorful | Java with Dynamic Programming or Greedy | $\text{\color{Dandelion}Medium}$ | Array, Dynamic Programming, Greedy, String | |
| 1592 | Rearrange Spaces Between Words | Java | $\text{\color{TealBlue}Easy}$ | String | |
| 1657 | Determine if Two Strings Are Close | Java with Sorting or Hash Table & Sorting | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting | |
| 1662 | Check If Two String Arrays are Equivalent | Java with or without Pointers | $\text{\color{TealBlue}Easy}$ | Array, String | |
| 1704 | Determine if String Halves Are Alike | Java | $\text{\color{TealBlue}Easy}$ | Counting, String | |
| 1832 | Check if the Sentence is Pangram | Java | $\text{\color{TealBlue}Easy}$ | Hash Table, String | Solution Using Bit Manipulation , Counting and Hash Table |
| 1869 | Longer Contiguous Segments of Ones than Zeros | Java | $\text{\color{TealBlue}Easy}$ | String | |
| 1935 | Maximum Number of Words You Can Type | Java | $\text{\color{TealBlue}Easy}$ | Hash Table, String | |
| 2023 | Number of Pairs of Strings With Concatenation Equal to Target | Java | $\text{\color{Dandelion}Medium}$ | Array, String | |
| 2129 | Capitalize the Title | Java | $\text{\color{TealBlue}Easy}$ | String | |
| 2131 | Longest Palindrome by Concatenating Two Letter Words | Java with Counting or Hash Table | $\text{\color{Dandelion}Medium}$ | Array, Counting, Greedy, Hash Table, String | |
| 2315 | Count Asterisks | Java | $\text{\color{TealBlue}Easy}$ | String | |
| 2351 | First Letter to Appear Twice | Java with Counting or Hash Table | $\text{\color{TealBlue}Easy}$ | Counting, Hash Table, String | |
| 2399 | Check Distances Between Same Letters | Java without or with Hash Table | $\text{\color{TealBlue}Easy}$ | Array, Hash Table, String | |
| 2437 | Number of Valid Clock Times | Java | $\text{\color{TealBlue}Easy}$ | Enumeration, String | |
| 2451 | Odd String Difference | Java without or with Hash Table | $\text{\color{TealBlue}Easy}$ | Hash Table, Math, String | |
| 2452 | Words Within Two Edits of Dictionary | Java | $\text{\color{Dandelion}Medium}$ | Array, String |
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Tree
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 94 | Binary Tree Inorder Traversal | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Depth-First Search, Stack, Tree | |
| 98 | Validate Binary Search Tree | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Search Tree, Binary Tree, Depth-First Search, Tree | |
| 100 | Same Tree | Java with Breadth-First Search or Depth-First Search | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 102 | Binary Tree Level Order Traversal | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Breadth-First Search, Tree | |
| 103 | Binary Tree Zigzag Level Order Traversal | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Breadth-First Search, Tree | |
| 104 | Maximum Depth of Binary Tree | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 107 | Binary Tree Level Order Traversal II | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Breadth-First Search, Tree | |
| 110 | Balanced Binary Tree | Java | $\text{\color{TealBlue}Easy}$ | Binary Tree, Depth-First Search, Tree | |
| 111 | Minimum Depth of Binary Tree | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 112 | Path Sum | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 113 | Path Sum II | Java with Backtracking and Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Backtracking, Binary Tree, Depth-First Search, Tree | |
| 114 | Flatten Binary Tree to Linked List | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Linked List, Stack, Tree | |
| 129 | Sum Root to Leaf Numbers | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Tree | |
| 144 | Binary Tree Preorder Traversal | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search, Depth-First Search, Stack, Tree | |
| 145 | Binary Tree Postorder Traversal | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search, Depth-First Search, Stack, Tree | |
| 222 | Count Complete Tree Nodes | Java | $\text{\color{Dandelion}Medium}$ | Binary Search, Binary Tree, Depth-First Search, Tree | |
| 226 | Invert Binary Tree | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 257 | Binary Tree Paths | Java with Backtracking and Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Backtracking, Binary Tree, Depth-First Search, String, Tree | |
| 404 | Sum of Left Leaves | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 429 | N-ary Tree Level Order Traversal | Java | $\text{\color{Dandelion}Medium}$ | Breadth-First Search, Tree | |
| 437 | Path Sum III | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Tree | |
| 559 | Maximum Depth of Binary Tree | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Breadth-First Search, Depth-First Search, Tree | |
| 653 | Two Sum IV - Input is a BST | Java with Breadth-First Search (with Hash Table), Breadth-First Search (without Hash Table), Depth-First Search (Iterative), Depth-First Search (Recursive), Two Pointers (with Iterative Inorder Traversal) or Two Pointers (with Recursive Inorder Traversal) | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Hash Table, Tree, Two Pointers | |
| 783 | Minimum Distance Between BST Nodes | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Tree | |
| 988 | Smallest String Starting From Leaf | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, String, Tree | |
| 1026 | Maximum Difference Between Node and Ancestor | Java with Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Depth-First Search, Tree | |
| 1457 | Pseudo-Palindromic Paths in a Binary Tree | Java with Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) | $\text{\color{Dandelion}Medium}$ | Binary Tree, Bit Manipulation, Breadth-First Search, Depth-First Search, Tree |
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Two Pointers
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 15 | 3Sum | Java | $\text{\color{Dandelion}Medium}$ | Array, Sorting, Two Pointers | |
| 16 | 3Sum Closest | Java | $\text{\color{Dandelion}Medium}$ | Array, Sorting, Two Pointers | |
| 19 | Remove Nth Node From End of List | Java with One Pass or Two Passes | $\text{\color{Dandelion}Medium}$ | Linked List, Two Pointers | |
| 26 | Remove Duplicates from Sorted Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Two Pointers | |
| 27 | Remove Element | Java | $\text{\color{TealBlue}Easy}$ | Array, Two Pointers | |
| 80 | Remove Duplicates from Sorted Array II | Java | $\text{\color{Dandelion}Medium}$ | Array, Two Pointers | |
| 88 | Merge Sorted Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | Solution Using Sorting |
| 151 | Reverse Words in a String | Java | $\text{\color{Dandelion}Medium}$ | String, Two Pointers | Solution Using Collections or StringBuilder |
| 167 | Two Sum II - Input Array is Sorted | Java | $\text{\color{Dandelion}Medium}$ | Array, Binary Search, Two Pointers | Solution Using Binary Search |
| 283 | Move Zeroes | Java | $\text{\color{TealBlue}Easy}$ | Array, Two Pointers | |
| 295 | Find Median from Data Stream | Java with Heap (Priority Queue) | $\text{\color{Red}Hard}$ | Data Stream, Design, Heap (Priority Queue), Sorting, Two Pointers | Use of Sorting & Two Pointers resulted in TLE (Time Limit Exceed) for large datasets. |
| 344 | Reverse String | Java | $\text{\color{TealBlue}Easy}$ | String, Two Pointers | |
| 345 | Reverse Vowels of a String | Java | $\text{\color{TealBlue}Easy}$ | String, Two Pointers | |
| 541 | Reverse String II | Java | $\text{\color{TealBlue}Easy}$ | String, Two Pointers | Solution Using StringBuilder |
| 556 | Next Greater Element III | Java | $\text{\color{Dandelion}Medium}$ | Math, String, Two Pointers | |
| 557 | Reverse Words in a String III | Java | $\text{\color{TealBlue}Easy}$ | String, Two Pointers | Solution Using String Builder |
| 567 | Permutation in String | Java | $\text{\color{Dandelion}Medium}$ | Hash Table, Sliding Window, String, Two Pointers | |
| 653 | Two Sum IV - Input is a BST | Java with Two Pointers (with Iterative Inorder Traversal) or Two Pointers (with Recursive Inorder Traversal) | $\text{\color{TealBlue}Easy}$ | Binary Search Tree, Binary Tree, Breadth-First Search, Depth-First Search, Hash Table, Tree, Two Pointers | Solution Using Breadth-First Search (with Hash Table), Breadth-First Search (without Hash Table), Depth-First Search (Iterative) or Depth-First Search (Recursive) |
| 876 | Middle of the Linked List | Java | $\text{\color{TealBlue}Easy}$ | Linked List, Two Pointers | |
| 905 | Sort Array By Parity | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | |
| 922 | Sort Array By Parity II | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | |
| 923 | 3Sum With Multiplicity | Java | $\text{\color{Dandelion}Medium}$ | Array, Counting, Hash Table, Sorting, Two Pointers | Solution Using Counting Hash Table |
| 948 | Bag of Tokens | Java | $\text{\color{Dandelion}Medium}$ | Array, Greedy, Sorting, Two Pointers | |
| 977 | Squares of a Sorted Array | Java | $\text{\color{TealBlue}Easy}$ | Array, Sorting, Two Pointers | Solution Using Sorting |
| 1089 | Duplicate Zeros | Java | $\text{\color{TealBlue}Easy}$ | Array, Two Pointers | Solution Without Two Pointers |
| 1346 | Check If N and Its Double Exist | Java | $\text{\color{TealBlue}Easy}$ | Array, Binary Search, Hash Table, Sorting, Two Pointers | Solution Using Binary Search & Sorting or Hash Table |
| 1679 | Max Number of K-Sum Pairs | Java | $\text{\color{Dandelion}Medium}$ | Array, Hash Table, Sorting, Two Pointers | Solution Using Hash Table |
| 2095 | Delete the Middle Node of a Linked List | Java | $\text{\color{Dandelion}Medium}$ | Linked List, Two Pointers | |
| 2130 | Maximum Twin Sum of a Linked List | Java with Two Pointers or Two Pointers & Stack | $\text{\color{Dandelion}Medium}$ | Linked List, Stack, Two Pointers |
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Union Find
| # | Problem | Solution | Difficulty | Topics | Note |
|---|---|---|---|---|---|
| 130 | Surrounded Regions | Java | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Depth-First Search, Matrix, Union Find | Solution Using Breadth-First Search or Depth-First Search |
| 200 | Number of Islands | Java | $\text{\color{Dandelion}Medium}$ | Array, Breadth-First Search, Depth-First Search, Matrix, Union Find | Solution Using Breadth-First Search or Depth-First Search |
| 1061 | Lexicographically Smallest Equivalent String | Java | $\text{\color{Dandelion}Medium}$ | String, Union Find | |
| 1971 | Find if Path Exists in Graph | Java | $\text{\color{TealBlue}Easy}$ | Breadth-First Search, Depth-First Search, Graph, Union Find | Solution Using Breadth-First Search, Depth-First Search (Iterative) or Depth-First Search (Recursive) |
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💻 Detailed Explanations for LeetCode Solutions in Java. Updated Daily.