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Metadata

My LeetCode practice source code and notes.

David's LeetCode Practice Build Status codecov

Testing

  • local dependencies
    • pytest
    • pytest-cov
    • coverage

Correctness (based on pytest)

Test all the units (in the main directory):

py.test -v

Code Coverage

pytest --cov-report term --cov Python3/

if successful you should see a new .coverage file

coverage report

Python3 Progress

Python 3.8

docker pull python:3.8

Symbols

  • Difficulty:
    • Harder: ▲
    • Same: -
    • Easier: ▼
  • Important: *
  • Good: 👍

Abbreviation

  • Algorithm
    • DP - Dynamic Programming
    • DC - Divide and Conquer
  • Data Structure
    • HT - Hash Table
    • BST - Binary Search Tree
    • PQ - Priority Queue (usually Heap)
  • Others
    • BM - Bit Manipulation

Naive means the first thought of mine (usually a little better than Brute-Force, but may need to be optimized.)

LeetCode Patterns

  • Leetcode Patterns – Medium
    • Leetcode Pattern 0 - Iterative traversals on Trees
    • Leetcode Pattern 1 - DFS + BFS
    • Leetcode Pattern 2 - Sliding Windows for Strings
    • Leetcode Pattern 3 - Backtracking
    • Leetcode Pattern 4 - Meta Stuff

Remark

  • Category
    • Category1, Category2, ...
    • Usually record in (input data) Data Structure. (The Algorithm (and additional/special Data Structure) strategy will be noted in the Method field)
    • Code will be put in the main category folder (i.e. the first one).
    • Some category may be the Related Topic tags marked by LeetCode.
    • (Add Pattern 0~4 in brackets)
    • TODO: Most of the categories need to be updated. (The date before 2018/9/22)
    • TODO: Mark "Good for Beginner" or "Good for Intermediate" etc.
    • TODO: Tags for search (special mark in file or filename)
Number Difficulty Problem Date Category Method-TimeComplexity Remark TODO
👍 001 Easy Two Sum 2018/3/12 Array, HT Naive-O(nlogn), HT-O(n), Sorted HT-O(n) Note -
002 Medium Add Two Numbers 2018/3/12 Linked List Naive-O(n) Note Make a shorter version
👍 003 Medium * Longest Substring Without Repeating Characters 2018/9/24 String, HT Sliding Window, Sliding Window Optimized Note -
👍 005 Medium * Longest Palindromic Substring 2019/2/28 String, DP Naive-O(n³), DP-O(n²), Expand Around Center-O(n²) Note -
006 Medium ZigZag Conversion 2018/3/22 Array Naive-O(n) Note -
007 Easy Reverse Integer 2018/3/22 Array Naive-O(n) Note -
008 Medium String to Integer (atoi) 2018/9/30 String (TODO: move to AdHoc) Naive-O(n) Note -
009 Easy Palindrome Number 2018/3/22 Array Naive-O(n), Without using string-O(n) Note -
010 Hard * Regular Expression Matching 2018/10/13 String DC-O((m+n) x 2ⁿ), Top-Down DP-O(mn), Bottom-Up DP-O(mn) Note -
👍 011 Medium * Container With Most Water 2018/9/22 Array Naive-O(n²), Two Pointer-O(n), Naive 2-O(n²), Two Pointer 2-O(n) Note -
012 Medium Integer to Roman TODO String (TODO: move to AdHoc) Naive-O(n) Note -
013 Easy Roman to Integer 2018/9/29 String (TODO: move to AdHoc) Naive-O(n) Note -
014 Easy Longest Common Prefix 2018/9/16 Array Naive-O(n*len) Note -
👍 015 Medium ▲ 3Sum 2018/10/13 Array TwoPointer-O(n²), Naive-O(n²), TwoPointer2-O(n²), BinarySearch-O(n²) Note do it again
016 Medium 3Sum Closest 2018/10/13 Array TwoPointer-O(n²) Note -
017 Medium Letter Combinations of a Phone Number 2019/3/1 String Backtracking-O(n!) Note -
👍 018 Medium ▲ 4Sum 2019/3/2 Array, HT GeneralizedTwoPointer-O(n³) Note -
019 Medium * Remove Nth Node From End of List 2019/3/3 Linked List HT-O(n), TwoPointer-O(n) Note, Sina Interview do it again
👍 020 Easy Valid Parentheses 2018/9/15 String, Stack Naive-O(n), Stack-O(n), HashTable-O(n) Note, Learn: Queue & Stack -
021 Easy * Merge Two Sorted Lists 2018/6/27 Linked List Better-O(n), Naive-O(n) Note -
👍 023 Hard * Merge k Sorted Lists 2018/6/26 Linked List Naive-O(kn), Naive 2-O(nlogn), DC-O(nlogk), DC 2-O(nlogk), Heap-O(nlogk) Note Compare K each time, attrgetter
👍 022 Medium * Generate Parentheses 2019/3/6 String Backtracking-O(n!), Naive-O(n!) Note -
024 Medium Swap Nodes in Pairs 2018/5/31 Linked List Naive-O(n), Recursive-O(n) Note -
026 Easy Remove Duplicates from Sorted Array 2018/6/14 Array Naive-O(n), Better-O(n) Note -
027 Easy Remove Element 2019/7/2 Array Naive-O(n), Naive2-O(n) Note -
028 Easy Implement strStr() 2019/7/2 String Naive-O(n) Note -
031 Medium ▲ Next Permutation 2019/3/4 Array SinglePass-O(n) Note Permutation with duplicates
👍 033 Medium * Search in Rotated Sorted Array 2019/3/5 Array BinarySearch-O(log(n)), BinarySearch2-O(log(n)) Note, FreeWheel 2020 Fall Recruit do it again
👍 035 Easy Search Insert Position 2019/7/3 Array BinarySearch-O(log(n)), Naive-O(log(n)), BinarySearch2-O(log(n)) Note -
036 Medium ▼ Valid Sudoku 2018/6/21 Array HT-O(n) Note -
037 Hard Sudoku Solver TODO Array Note -
038 Easy Count and Say 2019/9/30 String Naive-O(n) Note -
039 Medium Combination Sum 2019/3/7 Array Backtracking-O(n!), Naive-O(n!) Note improve time complexity by not use sort
👍 042 Hard * Trapping Rain Water TODO Array -
👍 044 Hard Wildcard Matching TODO String Note DP, NFA
👍 045 Medium * Jump Game II 2020/10/14 Array DP-O(n^2), Greedy-O(n^2), BFS-O(n^2), Greedy 2-O(n^2) do it again with all solutions
👍 046 Medium * Permutations 2018/5/31 Array Backtracking-O(n!), Recursive-O(n!), DFS Based-O(n!) Note -
👍 048 Medium * Rotate Image 2019/12/2 Array Naive-O(n) Note, Microsoft 2020 Fall Recruit -
👍 049 Medium * Group Anagrams 2019/12/3 String, HT Naive-O(nk), Sorting-O(nklogk), Counter-O(nk) Note testcase
👍 050 Medium * Pow(x, n) 2020/7/16 Math Naive-O(n), Recursive-O(logn), Recursive 2-O(logn), Bit Manipulation-O(logn) -
👍 051 Hard * N-Queens 2020/7/25 Array Naive-O(n^2) testcase, TODO: another slash way in isValid
052 Hard N-Queens II 2020/7/25 Array Naive-O(n^2) testcase, TODO: another slash way in isValid
👍 053 Medium * Maximum Subarray 2018/6/12 Array BruteForce-O(n³), DP-O(n), DC-O(nlogn) Note Do it again
👍 055 Medium * Jump Game 2020/4/26 Array Backtracking-O(2^n), DPTopDown-O(n^2), DPBottomUp-O(n^2), Greedy-O(n), Greedy2-O(n) Note, Good DP walk through -
056 Medium * Merge Intervals 2020/2/21 Array Sorting-O(nlogn), Naive-O(nlogn), Better-O(nlogn), Graph-O(n^2), Tree(Stream)-O(n^2) Note Improve performance
058 Easy Length of Last Word 2019/9/30 String Not even worth to do - -
👍 060 Medium * Permutation Sequence 2020/6/20 String Naive-O(n!), Backtracking-O(n!), Math-O(n) do it again (math one)
061 Medium * Rotate List 2020/10/7 Linked List Naive-O(n) do it again with better way
👍 062 Medium Unique Paths 2020/6/29 Array Naive-O(m+n), DP-O(mn) -
👍 064 Medium * Minimum Path Sum 2020/4/19 Array Backtracking-O(n!), Backtracking With Early Stop-O(n!), Naive-O(mn), NoAdditionalSpace-O(mn), DP-O(mn) -
066 Easy Plus One 2019/10/19 Array Naive-O(n), FullAdder - -
067 Easy Add Binary 2019/10/22 String Adder-O(n), Iterative-O(n), Python-O(n) - -
069 Easy Sqrt(x) 2019/10/22 Search Naive-O(n), BinarySearch-O(logn), BinarySearch2-O(logn), BinarySearch3-O(logn) - -
070 Easy Climbing Stairs 2018/6/13 DP DP-O(n), Recursive-O(n), Naive-O(n) Note -
071 Medium Simplify Path 2019/12/17 String Stack-O(n), Naive-O(n), Stack 2-O(n) Note -
👍 072 Hard * Edit Distance 2019/10/30 String DP-O(mn), Recursive-O(mⁿ), Recursive With Memory-O(mn), DP 2-O(mn) Note, Baidu Interview -
👍 075 Medium Sort Colors 2020/6/11 Array CountingSort-O(n), DutchNationalFlagProblem-O(n) Note testcase, do this again
👍 078 Medium Subsets 2018/6/27 BM Binary-O(2ⁿ), DFSBased-O(2ⁿ), Backtracking-O(2ⁿ), Naive-O(2ⁿ) Note -
👍 079 Medium * Word Search 2020/6/30 Array Naive-O(nlogn), DFS-O(mn4^s), DFS 2-O(mn4^s) do it again
082 Easy Remove Duplicates from Sorted List II 2021/1/5 Linked List Naive-O(n) - testcase
083 Easy Remove Duplicates from Sorted List 2019/10/22 Linked List Naive-O(n) - -
085 Hard Maximal Rectangle TODO Array Note -
👍 086 Medium * Partition List 2020/10/18 Linked List TwoPointer-O(n) Naive-O(n) Fix WA, do it again
088 Easy Merge Sorted Array 2019/11/18 Array Naive-O(n) -
089 Medium Gray Code 2021/7/1 BitManipulation Direct Ordering-O(n), Mirror Ordering-O(n), Binary to Gray-O(n), Better-O(n) -
091 Medium * Decode Ways 2020/9/28 Array Naive-O(n), Note TODO: Top-down DP, Bottom-up DP, Constant Space DP
👍 092 Medium * Reverse Linked List II 2020/9/20 Linked List Naive-O(n), OnePass-O(n) testcase, OnePass
093 Medium Restore IP Addresses 2019/12/16 Array Backtracking-O(nlogn) Note -
094 Medium Binary Tree Inorder Traversal 2018/5/29 Binary Tree Recursive-O(n), Iterative-O(n) Note -
👍 096 Medium * Unique Binary Search Tree 2020/6/24 Binary Tree Naive-O(n) testcase, do it again
098 Medium ▼ Validate Binary Search Tree 2018/6/25 BST Inorder-O(n), DFS-O(n) Note -
👍 100 Easy Same Tree 2019/11/20 Binary Tree Recursive-O(n), Naive-O(n) Note -
👍 101 Easy ▲ Symmetric Tree 2018/6/8 Binary Tree Recursive-O(n), Iterative-O(n), Preorder-O(n), Iterative BFS-O(n) Note -
102 Medium * Binary Tree Level Order Traversal 2018/6/7 Binary Tree BFS-O(n) Note -
👍 103 Medium * Binary Tree Zigzag Level Order Traversal 2020/7/22 Binary Tree Naive-O(n), Without Reverse-O(n), BFS-O(n), Without Reverse 2-O(n) Need to be able to right without reverse version solution -
👍 104 Easy Maximum Depth of Binary Tree 2018/6/8 Binary Tree Top-Down-O(n), Bottom-up-O(n), Top-Down2-O(n) Note -
105 Medium * Construct Binary Tree from Preorder and Inorder Traversal 2018/6/9 Binary Tree DC-O(n) Note -
106 Medium * Construct Binary Tree from Inorder and Postorder Traversal 2018/6/8 Binary Tree DC-O(n), Naive-O(n), Naive 2-O(nlogn), Naive 3-O(n), Better-O(n) Note test cases
107 Easy Binary Tree Level Order Traversal II 2019/12/30 Binary Tree Naive-O(n), Naive 2-O(n) - -
108 Easy Convert Sorted Array to Binary Search Tree 2019/11/13 BST Recursive-O(n) Note Test case
👍 109 Medium Convert Sorted List to Binary Search Tree 2019/11/13 BST Array Recursive-O(n), Two Pointer Recursive-O(nlogn) Note In-order Simulation, test case
👍 110 Easy ▲ Balanced Binary Tree 2019/12/30 Binary Tree Naive-O(n), Better Recursive-O(n), Postorder Iterative-O(n) Note do it again
111 Easy Minimum Depth of Binary Tree 2019/11/1 Binary Tree BFS-O(n) -
👍 112 Easy Path Sum 2018/6/8 Binary Tree Naive-O(n) Note Can be improved
👍 113 Medium Path Sum II 2019/12/23 Binary Tree Naive-O(n) Note -
👍 114 Medium Flatten Binary Tree to Linked List 2019/12/31 Binary Tree Naive-O(n) Note more elegant way
116 Medium Populating Next Right Pointers in Each Node 2019/12/24 Binary Tree Naive-O(n), DFS-O(n) Note Test
117 Medium * Populating Next Right Pointers in Each Node II 2019/12/24 Binary Tree DFS-O(n) Note Test
118 Easy Pascal's Triangle 2019/12/28 Array Naive-O(n) Note Faster approach (memory, recursive, iterative)
120 Medium * Triangle 2019/12/25 Array Naive-O(n) Note less space DP
👍 121 Easy * Best Time to Buy and Sell Stock 2018/6/13 Array BruteForce-O(n), Not so DP-O(n), Naive-O(n), DP-O(n) Note -
👍 122 Medium * Best Time to Buy and Sell Stock II 2018/6/14 Array Greedy-O(n), Tricky-O(n), Max-O(n), Greedy 2-O(n) Note -
👍 124 Hard * Binary Tree Maximum Path Sum 2020/4/29 BinaryTree Recursive-O(nlogn) - testcase, do this again
125 Easy Valid Palindrome 2020/1/2 String Naive-O(n), Naive2 (Two Pointer)-O(n) - -
127 Medium * Word Ladder 2019/12/25 String BFS-O(n) Note Bidirectional BFS
👍 128 Hard ▼ Longest Consecutive Sequence 2019/11/14 Array Naive-O(n²), HT-O(n) Note -
👍 129 Medium * Sum Root to Leaf Numbers 2020/6/26 Binary Tree Naive-O(nlogn), DFS-O(n), Stack DFS-O(n) -
👍 130 Medium Surrounded Regions 2020/3/25 Array Naive-O(mn), Boarders-O(mn) Note
👍 133 Medium * Clone Graph 2020/1/16 Graph Recursive-O(n), DFS-O(n), BFS-O(n) Note, Learn: Queue & Stack Do it again
👍 135 Hard * Candy 2021/6/27 Array Brute Force-O(n^2), Two arrays-O(n) do it again
👍 136 Easy Single Number 2019/12/18 Array HT-O(n), Set-O(n), BM-O(n) Note -
👍 137 Medium * Single Number II 2020/6/22 Array Naive-O(n), BitManipulation-O(n), BitManipulation 2-O(n), Math-O(n) testcase
👍 138 Medium * Copy List with Random Pointer 2021/2/10 Linked List Naive-O(n), Interweave-O(n), Map-O(n) testcase
👍 139 Medium Word Break 2020/1/14 String Recursive-O(2ⁿ), DP-O(n²) Note -
👍 140 Hard * Word Break II 2020/7/30 String Naive-O(n^2), Backtracking-O(n^2), DP Bottom up DP
141 Easy * Linked List Cycle 2019/12/31 Linked List Naive-O(n), TwoPointer-O(n), TwoPointer 2-O(n) Note, Microsoft testcase
👍 142 Medium * Linked List Cycle II 2020/6/25 Linked List Naive-O(n), Two Pointer-O(n), Two Pointer 2-O(n) testcase
143 Medium Reorder List 2020/3/25 Linked List Naive-O(n), Improved-O(n) testcase
144 Medium Binary Tree Preorder Traversal 2018/5/29 Binary Tree Recursive-O(n), Iterative-O(n) Note -
145 Hard ▼ Binary Tree Postorder Traversal 2018/6/2 Binary Tree Recursive-O(n), Iterative-O(n) Note -
👍 146 Medium * LRU Cache 2018/6/25 Design Naive, Queue, OrderedDict, DoubleLinkedList Note
147 Medium Insertion Sort List 2020/1/14 Linked List Naive-O(n²) Note Do it again with other style
👍 148 Medium * Sort List 2020/5/11 Linked List MergeSort-O(nlogn) Do it again, InsertionSort-O(n^2), testcase
👍 150 Medium Evaluate Reverse Polish Notation 2020/2/10 Array Stack-O(n) Note, Learn: Queue & Stack -
151 Medium * Reverse Words in a String 2019/10/22 String Pythonic-O(n), Trick-O(n), Naive-O(n), C Style-O(n) Note, Microsoft Intern Interview -
👍 153 Medium * Find Minimum in Rotated Sorted Array 2020/7/25 Array Naive-O(logn), Simpler-O(logn) -
👍 154 Hard * Find Minimum in Rotated Sorted Array II 2020/7/25 Array Naive-O(logn), YetAnother-O(logn) -
155 Easy Min Stack 2018/6/28 Design Naive, Improve Note, Learn: Queue & Stack Naive?!
165 Medium ▼ Compare Version Numbers 2023/2/23 String Naive-O(n), Improve-O(n) Follow up: Sort an Array of Version Numbers, testcase
167 Easy Two Sum II - Input array is sorted 2019/9/18 Array TwoPointer-O(n) Note -
169 Easy Majority Element 2020/5/6 Array Naive-O(n), Counter-O(n), Sorting-O(nlogn), Boyer-Moore Voting-O(n) -
👍 174 Hard * Dungeon Game 2020/6/21 Array DP-O(mn) do it again, TODO: bottom-up dp with binary search
189 Easy * Rotate Array 2018/6/14 Array NaiveInPlace-O(k), ExtraArray-O(n), Simplest-O(n) Note TODO: (Try all other solutions e.g. Cyclic Replacements / Reverse)
190 Easy Reverse Bits 2020/7/12 Bit Manipulation Naive-O(n), String-O(n) testcase
191 Easy Number of 1 Bits 2021/2/1 Bit Manipulation Naive-O(n) testcase, other alternatives
198 Easy House Robber 2018/6/14 DP DP-O(n) Note Can improve space complexity
👍 199 Medium * Binary Tree Right Side View 2021/2/6 Binary Tree Naive-O(n) testcase
👍 200 Medium * Number of Islands 2019/7/5 Search BFS-O(n²), DFS-O(n²) Note, Learn: Queue & Stack, Dropbox OA try Union, do this again
👍 201 Medium Bitwise AND of Numbers Range 2020/4/23 BitManipulation Naive-O(n), Improve-O(n)
202 Easy Happy Number 2020/4/2 Math Naive-O(n) testcase
203 Easy Remove Linked List Elements 2020/3/18 Linked List Dummy Node-O(n), Single Pointer-O(n) testcase
👍 204 Easy * Count Primes TODO Math -
206 Easy Reverse Linked List 2018/6/26 Linked List Iterative-O(n), Recursive-O(n) Note, Microsoft Intern Interview -
👍 207 Medium * Course Schedule 2020/7/18 Array CycleDetect-O(n), TopologicalSort-O(n), DFS-O(n) - do it again
👍 208 Medium * Implement Trie (Prefix Tree) 2018/6/24 Design Naive, Trie (using Hashmap), Trie (using Array), Trie 2 (using Hashmap) Note testcase
👍 210 Medium * Course Schedule II 2020/7/18 Array TopologicalSort-O(n) - do it again, testcase
👍 211 Medium * Add and Search Word - Data structure design 2020/6/30 Design Naive, RegEx, Tire, Self as Tire Note do it again
👍 212 Hard * Word Search II 2020/6/30 Array Tire-O(n) - do it again, testcase
👍 214 Hard * Shortest Palindrome ~~2020/11/8~~ TODO String Note
👍 215 Medium * Kth Largest Element in an Array 2019/9/18 Array Naive-O(nlogn), QuickSort-O(n), SelectionSortLike-O(nk), Heap (Cheat)-O(nlogn), Heap-O(nlogn), QuickSelect-O(n), QuickSelect2-O(n) Note, Microsoft Intern Interview do it again
👍 216 Medium * Combination Sum III TODO Math Naive-O(n) DP
👍 221 Medium * Maximal Square 2020/4/27 Array Naive-O(k x (mn)^2), BruteForce-O((mn)^2), DP-O(mn), Better DP-O(mn) Note -
👍 221 Medium * Count Complete Tree Nodes 2020/6/23 Binary Tree Naive-O(n), BinarySearch-O(n) testcase
225 Easy Implement Stack using Queues 2018/6/24 Design Two Queue Note, Learn: Queue & Stack -
👍 226 Easy * Invert Binary Tree 2020/6/1 Binary Tree Naive-O(n), Recursive-O(n) Note testcase
👍 230 Medium * Kth Smallest Element in a BST 2020/5/20 Binary Tree Naive-O(n), Iterative-O(n) Note testcase
231 Easy * Power of Two 2020/6/8 Math Naive-O(n), String-O(n), BitManipulation-O(n) do it again
232 Easy Implement Queue using Stacks 2018/6/24 Design Two Stack Note, Learn: Queue & Stack -
👍 235 Easy Lowest Common Ancestor of a Binary Search Tree 2021/6/30 Binary Tree Naive-O(n) -
👍 236 Medium Lowest Common Ancestor of a Binary Tree 2018/6/10 Binary Tree Naive-O(n), Naive 2-O(n), Elegant-O(n) Note, Naive 3-O(n) testcase
237 Easy Delete Node in a Linked List 2020/3/18 Linked List Naive-O(1) (not worth to do) testcase..
👍 238 Medium * Product of Array Except Self 2020/3/18 Array ProductList-O(n), ProductList2-O(n), SingleProductList-O(n) Note do it again
👍 239 Hard * Sliding Window Maximum TODO Array Naive-O(n^2), Monotonic Queue-O(n) Dropbox 2021 Summer Intern OA, Facebook 2021 Summer Intern OA do this now!!
242 Easy Valid Anagram 2021/2/11 String Naive-O(n) testcase
252 Easy * Meeting Rooms (premium) 2020/2/20 Array Sorting-O(nlogn) Note, Facebook -
👍 253 Medium * Meeting Rooms II (premium) 2020/3/14 Array Sorting-O(nlogn) Note, Facebook -
👍 257 Easy ▲ Binary Tree Paths 2018/6/11 Binary Tree Iterative-O(n), Recursive-O(n) Note, Learn: Queue & Stack -
258 Easy Add Digits 2020/3/18 Array Naive-O(n), Iterative-O(n), NoLoop-O(1) Note, Microsoft, not good -
👍 259 Medium * 3Sum Smaller (premium) TODO Array Similar with 611 do it again
👍 260 Medium * Single Number III 2020/6/22 Array Naive-O(n), BitManipulation-O(n)
263 Easy Ugly Number 2020/7/4 Array Naive-O(n)
👍 264 Medium * Ugly Number II 2020/7/4 Array PriorityQueue-O(n), DP-O(n) Note, Microsoft Intern Interview do it again
268 Easy Missing Number 2022/12/18 Array Naive-O(n^2), BitManipulation-O(n) testcase
👍 269 Hard * Alien Dictionary TODO Array -
278 Easy First Bad Version 2020/5/1 Iteractive Naive-O(logn) testcase
274 Medium H-Index 2020/6/18 Array CumulativeSum-O(n) sorting-based solution see 275 testcase, do it again
275 Medium H-Index II 2020/6/18 Array Linear-O(n), BinarySearch-O(n) testcase, do it again
👍 279 Medium * Perfect Squares 2019/8/22 Search BFS-O(n), Recursive-O(n!), Top-Down DP-O(n), Linear Check-O(n * sqrt(n)), Bottom-Up DP-O(n), Math-O(sqrt(n)) Note do it again
👍 285 Medium * Inorder Successor in BST (premium) ~~2020/11/2~~ TODO Binary Tree Iterative-O(logn) Note do it again, testcase
👍 287 Medium Find the Duplicate Number 2020/6/25 Array Naive-O(n^2), TwoPointer(Linked List)-O(n), Set-O(n), Linked List-O(n) do it again, testcase
283 Easy Move Zeroes 2020/4/4 Array Naive-O(n), TwoPointer-O(n) - testcase
284 Medium Peeking Iterator 2021/2/8 Design Naive-O(1) - testcase
290 Easy Word Pattern 2022/12/18 String HashMap-O(n) - -
297 Hard Serialize and Deserialize Binary Tree 2019/11/14 Binary Tree Naive-O(n), Naive2-O(n) Note do it again with pre-order + queue
👍 300 Medium * Longest Increasing Subsequence 2019/11/11 Array BruteForce-O(2ⁿ), MemoryRecursive-O(n²), DP-O(n²), BinarySearch-O(nlogn), DP 2-O(n²), BinarySearch 2-O(nlogn) Note do it again
303 Easy * Range Sum Query - Immutable 2021/7/3 Design PrefixSum-O(1) Good for beginner -
👍 304 Medium * Range Sum Query 2D - Immutable 2021/7/3 Design Naive-O(n^2), PrefixSum-O(1) -
👍 309 Medium * Best Time to Buy and Sell Stock with Cooldown 2020/7/29 Array StateMachine-O(n), DP-O(n), StateMachine_DP-O(n) do it again
👍 310 Medium * Minimum Height Trees ~~2020/11/8~~ TODO Graph -
👍 315 Hard * Count of Smaller Numbers After Self 2021/6/26 Array Binary Index Tree-O(nlogn), Merge Sort-TODO Note do it again
👍 316 Medium * Remove Duplicate Letters 2020/10/11 String Greedy-O(n) do it again
👍 322 Medium * Coin Change 2020/10/5 Array Naive-O(n), DP-O(n * a) testcase, do it again
👍 324 Medium * Wiggle Sort II 2021/2/7 Array Naive-O(n), Median-O(n) testcase, DO IT AGAIN
👍 328 Medium * Odd Even Linked List 2020/5/16 Linked List Naive-O(n) testcase, do it again
👍 329 Hard * Longest Increasing Path in a Matrix 2021/7/30 Graph DFS do it again
👍 330 Hard Patching Array 2020/8/17 Array Naive-O(n^2), Trick-O(n) -
👍 332 Medium * Reconstruct Itinerary 2020/6/28 Array Naive-O(n), EulerianPath-O(ElogE), DFS-O(nlogn) do it again
338 Easy Counting Bits 2022/12/18 BitManipulation Naive-O(n), Naive2-O(n) -
* 342 Easy Power of Four 2020/8/4 Math Naive-O(n), Bit Manipulation-O(n), Iterative-O(n), Recursive-O(n), Math-O(n) More bit manipulation solution -
344 Easy Reverse String 2020/6/4 String Naive-O(n), Recursive-O(n) Note testcase
👍 347 Medium * Top K Frequent Elements 2019/9/27 Array Naive-O(nlogn), HT Heap-O(nlogk), HT Heap 2-O(nlogk), Quickselect-avg O(n), Bucket Sort-O(n), HT-O(n) Note -
363 Hard * Max Sum of Rectangle No Larger Than K 2021/7/3 Array Prefix Sum-O(m^2 n^2) Similar problem: 325, 363, 560, 974, 1074 do it again
367 Easy Valid Perfect Square 2020/5/9 Math Naive-O(n), BinarySearch-O(n) - testcase
👍 368 Medium Largest Divisible Subset 2020/6/13 Array Naive-O(n!), DP-O(n²) Note do it again (DP)
👍 373 Medium Find K Pairs with Smallest Sums 2020/5/3 Array Priority Queue-O(klogk), Heap Merge Sort related to 1439 (competition) testcase, do it again
👍 376 Medium Wiggle Subsequence 2020/9/13 Array Naive-O(n), BottomUpDP-O(n)
👍 378 Medium Kth Smallest Element in a Sorted Matrix 2021/7/7 Array Naive-O(n^2logn) Note do it again (merge sort, binary search)
380 Medium Insert Delete GetRandom O(1) 2020/6/12 Design Naive-O(1) testcase, use HT + array
👍 382 Medium * Linked List Random Node 2023/3/10 Linked List Naive-O(n), Weighted Sampling-O(n), ReservoirSampling-O(n) test cases
383 Easy Ransom Note 2020/5/4 String Naive-O(n), Better-O(n) - -
387 Easy First Unique Character in a String 2020/5/5 String Naive-O(n) - testcase
392 Easy Is Subsequence 2020/6/9 String Naive-O(n) -
👍 402 Medium Remove K Digits 2020/5/13 String Naive-O(n) do this again
404 Easy Sum of Left Leaves 2020/8/1 BinaryTree Naive-O(n) - testcase
👍 406 Medium * Queue Reconstruction by Height 2020/6/6 Array Sorting-O(n^2), InsertFromLowest-O(nlogn), InsertFromHighest-O(nlogn), Insert-O(n) Note do it again, testcase
👍 413 Medium * Arithmetic Slices 2021/2/18 Array Naive-O(n) testcase, do it again
👍 416 Medium * Partition Equal Subset Sum TODO Array -
419 Medium Battleships in a Board TODO Array
👍 426 Medium Convert Binary Search Tree to Sorted Doubly Linked List TODO BST Need subscription -
427 Medium Construct Quad Tree TODO Graph Naive
👍 430 Medium * Flatten a Multilevel Doubly Linked List 2020/7/10 Linked List Naive-O(n), Stack-O(n) do it again, testcase
👍 435 Medium * Non-overlapping Intervals TODO Array
👍 438 Medium Find All Anagrams in a String 2020/5/17 String Naive-O(n) -
👍 441 Easy Arranging Coins 2020/7/1 Math Naive-O(n), Binary Search-O(logn), Math-O(1) -
443 Medium String Compression 2023/3/2 String Naive-O(n), Two Pointer-O(n), Two Pointer 2-O(n) -
👍 451 Medium Sort Characters By Frequency 2020/5/22 String Naive-O(n), PQ-O(n) testcase
👍 452 Medium Minimum Number of Arrows to Burst Balloons 2020/10/10 Array Naive-O(nlogn) -
460 Hard LFU Cache 2018/6/25 Design Naive Note OrderedDict, LinkedList
461 Easy Hamming Distance 2020/7/5 Bit Manipulation Naive-O(n) testcase
👍 463 Easy Island Perimeter 2020/7/7 Array Naive-O(n), Neighbour-O(n), CountEdge-O(n), StringEdge-O(n) testcase
👍 468 Medium Validate IP Address 2020/6/16 String Naive-O(n) Microsoft Intern Interview todo: pure regex, pure rule
👍 477 Medium Total Hamming Distance TODO Bit Manipulation string approach
👍 494 Medium Target Sum 2020/2/10 Array Naive-O(n²), RecursiveWithMemory-O(l*n), 2D DP-O(l*n), 1D DP-O(l*n) Note, Learn: Queue & Stack more optimization on DP
👍 518 Medium * Coin Change 2 2020/6/7 Array Naive-O(n^t), DP-O(nt) Note do it again (bottom up 1D DP)
👍 502 Hard IPO 2023/2/23 Array Naive-O(kn), SortHeap-O(nlogn), SortHeapImprove-O(nlogn) -
👍 503 Medium * Next Greater Element II TODO Array -
👍 516 Medium * Longest Palindromic Subsequence 2023/4/14 String Top-Down DP-O(n²), Bottom-Up DP-O(n²), Bottom-Up DP-O(n²) O(n) space O(n) Space Bottom-Up DP, Follow Up (list result)
520 Easy Detect Capital 2020/8/3 String Naive-O(n), CapitalCount-O(n), RegEx-O(n) -
👍 525 Medium * Contiguous Array 2020/4/13 Array Naive-O(n²), HT-O(n), ExtraArray-O(n), HT2-O(n) Didi Interview do it again
👍 526 Medium Beautiful Arrangement 2021/1/3 Array BruteForce-O(n!), Backtracking with Memory testcase
528 Medium * Random Pick with Weight 2020/6/5 Design Naive-O(n), Naive2-O(n), Binary Search-O(n), OnePass-O(n) Note testcase
532 Medium K-diff Pairs in an Array 2020/10/3 Array Naive-O(n^2), HT-O(n), Naive2-O(n) testcase
👍 538 Medium * Convert BST to Greater Tree 2021/2/7 BinaryTree DFS-O(n), Array-O(n) same as problem 1038 testcase, do it again
👍 540 Medium Single Element in a Sorted Array 2020/5/12 Array Naive-O(n), BinarySearchXOR-O(logn), XOR-O(n), BinarySearch-O(logn) -
👍 543 Easy Diameter of Binary Tree 2020/4/11 Binary Tree DFS-O(n) testcase
👍 547 Medium Friend Circles ~~2020/11/2~~ TODO Graph DFS-O(n) testcase
559 Easy Maximum Depth of N-ary Tree 2019/11/14 Tree Naive-O(n), DFS-O(n) Note Test
👍 560 Medium Subarray Sum Equals K 2020/4/22 Array BruteForce-O(n^3), CumulativeSum-O(n²), WithoutSpace-O(n²), HT-O(n) Note
563 Easy Binary Tree Tilt 2020/8/1 BinaryTree Naive-O(n) iterative
566 Easy Reshape the Matrix 2021/7/5 Array Naive-O(n) Good for beginner -
👍 567 Medium Permutation in String 2020/5/18 String Naive-O(n) testcase
594 Easy Longest Harmonious Subsequence 2021/2/4 Array Naive-O(n) testcase
605 Easy Can Place Flowers 2023/3/20 Array Naive-O(n) -
👍 611 Medium * Valid Triangle Number 2023/2/28 Array Brute Force-O(n^3), Binary Search-O(n^2logn), Binary Search 2-O(n^2logn), Two Pointer-O(n^2) Byte Dance Interview -
👍 621 Medium * Task Scheduler 2020/7/28 Array Naive-O(nlogn) Note TODO: more solution
👍 624 Easy Maximum Distance in Arrays (premium) 2020/10/5 Array Naive-O(n) -
👍 630 Hard * Course Schedule III 2021/5/2 Array Naive-O(n+1!), Top-down DP-O(n * d), PriorityQueue-O(nlogn) - topological sort, Do it again (all total official has 6)
👍 636 Medium * Exclusive Time of Functions 2020/10/25 Ad Hoc Naive-O(n) testcase
639 Hard Decode Ways II TODO String - -
👍 658 Medium * Find K Closest Elements 2021/7/2 Array Naive-O(logn + k), Double Sort-O(nlogn + klogk), Find Left Bound-O(log(n - k) + k) Note do it again
👍 662 Medium * Maximum Width of Binary Tree 2020/7/9 Binary Tree Naive-O(n) Note do it again (more elegant way), testcase
👍 665 Medium * Non-decreasing Array 2021/5/4 Array Greedy-O(n) Note do it again
👍 669 Medium * Trim a Binary Search Tree 2021/2/2 Binary Tree Recursive DFS-O(n) do it again
👍 673 Medium Number of Longest Increasing Subsequence TODO String
👍 674 Easy Longest Continuous Increasing Subsequence TODO String
👍 678 Medium * Valid Parenthesis String 2020/4/17 String Naive-O(n*3^n), DP-O(n), Greedy-O(n) Note do this again
👍 684 Medium * Redundant Connection 2020/10/18 Graph DSU-O(n), Union Find-O(n), Cycle Prevention DFS-O(n^2) do this again, DFS, BFS
👍 685 Hard Redundant Connection II TODO Graph DSU
687 Medium Longest Univalue Path TODO Binary Tree Note -
👍 698 Medium * Partition to K Equal Sum Subsets TODO Array -
700 Easy Search in a Binary Search Tree 2020/6/15 Binary Tree Naive-O(logn) testcase
701 Medium * Insert into a Binary Search Tree 2020/10/6 Binary Tree Naive-O(logn), Recursive-O(logn) testcase
703 Easy Kth Largest Element in a Stream 2020/5/8 Design Naive-O(n), Heap-O(n) Note testcase
704 Easy * Binary Search 2020/5/9 Array Iterative(<)-O(logn), Recursive(<=)-O(logn), Bisect-O(logn) -
705 Easy Design HashSet 2020/8/2 Design Naive-O(1), With Hash Function-O(1) testcase
733 Easy Flood Fill 2020/5/11 Array Naive-O(n), DFS-O(n), IterativeDFS-O(n) Test
👍 718 Medium * Maximum Length of Repeated Subarray 2021/7/8 Array DP-O(mn) Binary Search with Rolling Hash
👍 739 Medium Daily Temperatures 2019/12/26 Array Naive-O(n²), Naive2-O(n²), Stack-O(n²) Note, Learn: Queue & Stack -
👍 745 Hard * Prefix and Suffix Search 2021/5/1 Design RegularExpression-O(n), Paired Trie-O(nk^2 + qk), Trie of Suffix Wrapped Words-O(nk^2 + qk), Double Set-O(n) -
👍 752 Medium Open the Lock 2019/7/5 Search BFS-O(n²) Note, Learn: Queue & Stack Improve time complexity
👍 763 Medium Partition Labels 2020/9/5 String Naive-O(n)
771 Easy Jewels and Stones 2020/5/2 String Naive-O(n), Naive2-O(n) testcase
👍 783 Easy Minimum Distance Between BST Nodes 2023/2/17 Binary Tree DFS-O(n), DFS Improve-O(n) testcase
👍 784 Easy Letter Case Permutation 2020/7/25 String Naive-O(n), Naive 2-O(n) testcase, more elegant way
👍 785 Medium * Is Graph Bipartite? 2021/2/14 Graph Color-O(V + E) do it again
👍 787 Medium * Cheapest Flights Within K Stops 2020/6/14 Graph Naive-O(V + E), BFS-O(V + E), DP-O(n²), Naive 2-O(V + E) Note do it again
790 Medium Domino and Tromino Tiling TODO Geometry -
👍 797 Medium * All Paths From Source to Target 2020/7/24 Graph Naive-O(2^n), Backtracking-O(2^n) do it again, TODO: iterative version
801 Medium Minimum Swaps To Make Sequences Increasing TODO Array Note -
821 Easy Shortest Distance to a Character 2021/2/7 String Naive-O(n) testcase, more simple approach
829 Hard * Consecutive Numbers Sum TODO Math -
👍 834 Hard * Sum of Distances in Tree 2022/12/22 Graph Naive-O(n^3), SubtreeSumAndCount-O(n) do it again
841 Medium Keys and Rooms 2022/12/20 Graph DFS-O(n), DFS (loop)-O(n)
842 Medium Split Array into Fibonacci Sequence 2022/12/20 String Backtracking-O(n^m)
844 Easy Backspace String Compare 2020/4/9 String Naive-O(n), TwoPointer-O(n) testcase
👍 857 Hard * Minimum Cost to Hire K Workers 2020/3/17 Array Greedy-O(n²logn), Greedy w/ PQ-O(nlogn) Note -
859 Easy Buddy Strings 2020/10/12 String Naive-O(n^2), Naive-O(n), Better-O(n) testcase
👍 862 Hard * Shortest Subarray with Sum at Least K TODO Array Note Deque
867 Easy Transpose Matrix 2023/2/21 Array Naive-O(n), Numpy-O(n) testcase
👍 870 Medium Advantage Shuffle 2023/3/9 Array Sorting-O(n), SortingWithQueue-O(n) -
👍 875 Medium Koko Eating Bananas 2020/8/8 Array Naive-O(n), BinarySearch-O(n) testcase
876 Easy Middle of the Linked List 2020/4/8 Linked List Naive-O(n), TwoPointer-O(n) testcase
👍 881 Medium ▼ Boats to Save People 2023/4/3 Array Greedy-O(nlogn) Follow up: 1986
👍 886 Medium * Possible Bipartition 2022/12/21 Graph BFS-O(n) do it again
👍 901 Medium Online Stock Span 2020/5/19 Design Naive-O(n), Count-O(n), Stack-O(n) testcase
👍 904 Medium Fruit Into Baskets 2023/2/7 Array Naive-O(n^2), SlidingWindow-O(n), Greedy-O(n) -
👍 912 Medium * Sort an Array 2023/3/1 Array Quick Sort-O(nlogn), 3-Way Quick Sort-O(nlogn) TODO, Heap Sort-O(nlogn), Heap Sort 2-O(nlogn) TODO, Merge Sort-O(nlogn) TODO Implement all other O(nlogn) sorting algorithms
916 Medium Word Subsets 2020/9/5 String Naive-O(n), Improve-O(n), Counter-O(n) testcase
👍 918 Medium * Maximum Sum Circular Subarray 2020/5/15 Array Naive-O(n), MinSumSubarray-O(n) Note use other approach
933 Easy Number of Recent Calls 2020/10/1 Design Naive-O(n), Naive2-O(n), BinarySearch-O(logn), Queue-O(min(n, 3000)), CircularList-O(n) testcase
944 Easy Delete Columns to Make Sorted 2023/1/3 Array Naive-O(n) testcase
👍 946 Medium * Validate Stack Sequences 2023/4/13 Array Naive-O(n), Better-O(n) -
👍 952 Hard * Largest Component Size by Common Factor TODO Array
957 Medium Prison Cells After N Days 2020/7/3 Array Naive-O(n), LoopDetection-O(n) Note-O(n)
👍 958 Medium * Check Completeness of a Binary Tree 2023/3/15 Binary Tree BFS-O(n), DFS-O(n) Note testcase, do it again
👍 978 Medium Longest Turbulent Subarray TODO String
👍 986 Medium * Interval List Intersections 2020/5/23 Array TwoPointer-O(m+n) Note testcase, do it again
989 Easy Add to Array-Form of Integer 2023/2/15 Array Naive-O(n), Python-O(n) -
993 Easy Cousins in Binary Tree 2020/5/7 Binary Tree IterativeBFS-O(n), RecursiveDFS-O(n) testcase
👍 994 Medium Rotting Oranges 2020/9/13 Graph Naive-O(V + E)
997 Easy Find the Town Judge 2020/5/10 Array Naive-O(n), Improve-O(n), Naive 2-O(n)
👍 1004 Medium Max Consecutive Ones III 2021/6/29 Array Naive-O(n) -
1008 Medium Construct Binary Search Tree from Preorder Traversal 2020/4/20 Binary Tree Naive-O(n), Naive2-O(n) Note testcase
1009 Easy Complement of Base 10 Integer (Number Complement) 2020/5/4 BitManipulation Naive-O(n), Pythonic-O(n), BM-O(n) testcase
👍 1010 Easy Pairs of Songs With Total Durations Divisible by 60 2020/10/14 Array Naive-O(n^2), PrefixSum-O(n) testcase
👍 1011 Medium * Capacity To Ship Packages Within D Days 2023/2/22 Array BinarySearch-O(nlogn), BinarySearchImprove-O(nlogn) -
👍 1020 Medium * Number of Enclaves 2023/4/7 Graph DFS-O(n), Simpler DFS-O(n) -
👍 1029 Easy * Two City Scheduling 2020/6/3 Array Naive-O(nlogn), Diff-O(nlogn), Sorting-O(nlogn) -
👍 1035 Medium * Uncrossed Lines 2020/5/25 Array Naive-O(mn), BottomUpDP-O(mn) Note testcase, do it again
👍 1041 Medium Robot Bounded In Circle 2020/11/8 Array Naive-O(n) LinkedIn 2021 Summer Intern testcase, do it again
👍 1044 Hard Longest Duplicate Substring 2020/6/20 String Naive, BinarySearch-RabinKarp-O(nlogn) Note do it again
👍 1046 Easy * Last Stone Weight 2020/4/12 Array Heap-O(nlogn), Insertion Sort-O(nlogn) -
1047 Easy Remove All Adjacent Duplicates In String 2021/6/28 String Naive-O(n^n), Stack-O(n), Remove Pattern-O(n) Good for beginner -
1071 Easy Greatest Common Divisor of Strings 2022/12/19 String Naive-O(n^n) -
👍 1091 Medium Shortest Path in Binary Matrix 2021/2/13 Graph Naive-O(n) testcase
👍 1094 Medium Car Pooling 2020/9/21 Array Naive-O(n) testcase
👍 1143 Medium * Longest Common Subsequence 2019/10/22 String Brute Force-O(2ⁿ), DP-O(mn) Note, Baidu Interview (twice), DP + Return Subsequence Follow Up: Nowcoder - Return Subsequence Itself
👍 1200 Medium * Minimum Absolute Difference TODO Array -
👍 1220 Hard * Count Vowels Permutation 2021/7/4 Math DP-O(5n) good DP problem do it again
1232 Easy Check If It Is a Straight Line 2020/5/8 Math Naive-O(n) -
👍 1249 Medium * Minimum Remove to Make Valid Parentheses 2020/7/25 String Naive-O(n), Naive 2-O(n) stack, follow up: O(1) space
👍 1277 Medium Count Square Submatrices with All Ones 2020/5/22 String Naive-O(n^4), DP-O(mn) testcase, do it again
👍 1288 Medium Remove Covered Intervals 2020/10/4 Array Naive-O(n) testcase, do it with other solution
👍 1291 Medium Sequential Digits 2019/12/15 Math Naive-O(n), Recursive-O(nlogn), Naive2-O(n) Weekly Contest 167 testcase, Naive2 (generate sequence in order)
👍 1293 Hard * Shortest Path in a Grid with Obstacles Elimination 2021/7/30 Graph BFS Google Interview do it again
👍 1319 Medium Number of Operations to Make Network Connected 2023/3/23 Graph DFS-O(n) union find
👍 1312 Hard * Minimum Insertion Steps to Make a String Palindrome 2023/4/22 String Top-Down DP-O(n), Bottom-Up DP-O(n) (TODO) Similar to 72 Edit Distance Bottom-Up DP (see faster solution)
👍 1337 Easy The K Weakest Rows in a Matrix 2021/2/15 Array Naive-O(n) max heap + binary search
1338 Medium ▼ Reduce Array Size to The Half 2021/7/6 Array Naive-O(n) -
1342 Easy Number of Steps to Reduce a Number to Zero 2020/9/20 Math Naive-O(n), Naive 2-O(n) Good for beginner -
👍 1344 Medium Angle Between Hands of a Clock 2020/7/14 Math Naive-O(1) -
1379 Medium ▼ Find a Corresponding Node of a Binary Tree in a Clone of That Tree 2021/1/2 Binary Tree Naive-O(n) Note testcase, iterative
👍 1425 Hard Constrained Subsequence Sum TODO Array Note -
👍 1444 Hard Number of Ways of Cutting a Pizza 2023/3/31 Array Prefix Sum + DP-O(kmn) do it again
👍 1462 Medium * Course Schedule IV TODO Array - - -
👍 1466 Medium * Reorder Routes to Make All Paths Lead to the City Zero 2023/3/25 Graph BFS-O(n) - do it again (faster), testcases
1472 Medium Design Browser History 2023/3/18 Design Naive testcase
👍 1475 Easy * Final Prices With a Special Discount in a Shop 2020/8/22 Array Naive-O(n^2), TwoPointer-O(n^2), Stack-O(n^2) -
👍 1480 Easy * Running Sum of 1d Array 2021/5/3 Array Naive-O(n), In-Place-O(n) -
1491 Easy Average Salary Excluding the Minimum and Maximum Salary 2023/5/1 Array Naive-O(n) Good for beginner -
👍 1539 Easy Kth Missing Positive Number 2021/1/6 Array Naive-O(n+k), Naive 2-O(n), Binary Search-O(logn), Bisect-O(logn) - -
👍 1547 Hard Minimum Cost to Cut a Stick 2020/10/17 Array Top-Down DP-O(n^2) FreeWheel 2020 OA, Weekly Contest 201 testcase
👍 1572 Easy Matrix Diagonal Sum 2023/5/8 Array Naive-O(n), Better-O(n) - -
👍 1601 Hard Maximum Number of Achievable Transfer Requests 2020/9/28 Graph Naive-O(2^n) testcase
👍 1640 Easy Check Array Formation Through Concatenation 2021/1/1 Array DFS-O(n), HashTable-O(n) Weekly Contest 213, Note testcase, do it again
👍 1675 Hard Minimize Deviation in Array 2023/2/24 Array Greedy-O(nlogn) do it again, testcase
1768 Easy Merge Strings Alternately 2023/4/18 String Naive-O(n) Good for beginner -
👍 1834 Medium Single-Threaded CPU 2022/12/29 Array Greedy-O(n^2), Heap-O(nlogn), HeapImprove-O(nlogn) -
1822 Easy Sign of the Product of an Array 2023/5/2 Math Python-O(n), Naive-O(n), Better-O(n) Good for beginner -
👍 1861 Medium Rotating the Box TODO AdHoc Code Signal -
👍 1986 Medium * Minimum Number of Work Sessions to Finish the Tasks TODO Array -
👍 1928 Hard * Minimum Cost to Reach Destination in Time TODO Graph Google Interview -
👍 1971 Easy Find if Path Exists in Graph 2022/12/19 Graph BFS-O(n), DFS-O(n), UnionFind-O(n)
👍 2099 Easy Find Subsequence of Length K With the Largest Sum 2023/2/23 Array Naive-O(n) better testcase
👍 2187 Medium Minimum Time to Complete Trips 2023/3/7 Array Binary Search-O(nlogn) -
👍 2244 Medium Minimum Rounds to Complete All Tasks 2023/1/4 Array Greedy-O(n), Greedy2-O(n) -
👍 2279 Medium Maximum Bags With Full Capacity of Rocks 2022/12/27 Array Greedy-O(n) -
👍 2316 Medium *▲ Count Unreachable Pairs of Nodes in an Undirected Graph 2023/3/25 Graph Union Find (TLE) - O(n), Union Find Improve - O(n), DFS-O(n), BFS-O(n) other solution, testcases
👍 2348 Medium Number of Zero-Filled Subarrays 2023/3/21 Array Math-O(n), Simplified Math-O(n) other solutions
👍 2360 Hard * Longest Cycle in a Graph 2023/3/26 Graph DFS With Time-O(n) topological sort
2390 Medium ▼ Removing Stars From a String 2023/4/11 String Stack-O(n) -
👍 2405 Medium ▼ Optimal Partition of String 2023/4/4 String Greedy-O(n) try other solution
👍 2439 Medium ▲ Minimize Maximum of Array 2023/4/5 Array GreedyBruteForce-O(n*max(nums)), Binary Search-O(n*max(nums)), Prefix Sum-O(n) -
👍 2492 Medium Minimum Score of a Path Between Two Cities 2023/3/23 Graph BFS-O(n), Union Find-O(n) DFS, Union-Find
??? Easy Counting Elements 2020/4/7 Array Naive-O(nlogn), SinglePass-O(n) testcase
??? Easy Perform String Shifts 2020/4/15 String Naive-O(n) testcase
??? Easy Leftmost Column with at Least a One 2020/4/21 Interactive Naive-O(mn), BinarySearch-O(n), Improve-O(n+m) Note testcase, do this again
??? Easy First Unique Number 2020/4/28 Design Naive, HT Counter, Double Linked List, Double Linked List + HT Note testcase, improve follow the hint (set, heap)
??? Easy Check If a String Is a Valid Sequence from Root to Leaves Path in a Binary Tree 2020/4/30 Binary Tree Naive testcase, improve (like iterative dfs)

LintCode

Number Difficulty Problem Date Category Method-TimeComplexity Remark TODO
👍 127 Medium Topological Sorting 2023/2/23 Graph BFS-O(nlogn) DFS, testcase, do it again
👍 391 Medium Number of Airplanes in the Sky 2023/2/16 Array HeapSort-O(nlogn), SweepLine-O(nlogn) Do it again

Contest

LeetCode Learn Progress

LeetCode Explore Learn

Introduction to Algorithm

Introduction to Data Structure

Learning about...

Design Date Category Implementation Remark TODO
Circular Queue 2019/7/4 Data Structure C++ Note, Design Circular Queue -
Min Stack 2019/12/26 Data Structure C++ Min Stack -

Notes

Data Structure

  • Queue and Stack
  • Binary Tree
  • Priority Queue and Heap
  • Trie (prefix tree)
  • Fenwick Tree / Binary Indexed Tree (TODO)
  • Disjoint Set (Union-Find)

Algorithm

  • Dynamic Programming
  • Binary Search

DIY Progress

Data Structure

Difficulty Problem Date Category Method-TimeComplexity Remark TODO
Easy Linked List 2018/3/12 Linked List Singly-Linked List - Double-Linked List
Medium * Binary Heap (Min/Max Heap) 2018/6/28 Design Binary Heap Note -

Classic Algorithm Problem

Difficulty Problem Date Category Method-TimeComplexity Remark TODO
Easy Linked List 2018/3/12 Linked List Singly-Linked List - Double-Linked List
Medium * Binary Heap (Min/Max Heap) 2018/6/28 Design Binary Heap Note -

Resources

Online Judgement / Assessment

Paid

  • AlgoExpert

  • Grokking Dynamic Programming Patterns for Coding Interviews

    1. 0/1 Knapsack
      • Equal Subset Sum Partition
      • Subset Sum
      • Minimum Subset Sum Difference
      • Count of Subset Sum
      • Target Sum
    2. Unbounded Knapsack
      • Unbounded Knapsack
      • Rod Cutting
      • Coin Change
      • Minimum Coin Change
      • Maximum Ribbon Cut
    3. Fibonacci Numbers (Fibonacci Sequence (eg: House Thief, Jump Game))
      • Fibonacci numbers
      • Staircase
      • Number factors
      • Minimum jumps to reach the end
      • Minimum jumps with fee
      • House thief
    4. Palindromic Subsequence (Shortest Path (eg: Unique Paths I/II))
      • Longest Palindromic Subsequence
      • Longest Palindromic Substring
      • Count of Palindromic Substrings
      • Minimum Deletions in a String to make it a Palindrome
      • Palindromic Partitioning
    5. Longest Common Substring
      • Longest Common Substring
      • Longest Common Subsequence
      • Minimum Deletions & Insertions to Transform a String into another
      • Longest Increasing Subsequence
      • Maximum Sum Increasing Subsequence
      • Shortest Common Super-sequence
      • Minimum Deletions to Make a Sequence Sorted
      • Longest Repeating Subsequence
      • Subsequence Pattern Matching
      • Longest Bitonic Subsequence
      • Longest Alternating Subsequence
      • Edit Distance
      • Strings Interleaving

  • 0/1 Knapsack

  • Unbounded Knapsack

  • Shortest Path (eg: Unique Paths I/II)

  • Fibonacci Sequence (eg: House Thief, Jump Game)

  • Longest Common Substring/Subsequeunce

Course

Books

LeetCode Links

2020 Coronavirus quarantine special events

Top Interview Questions

LeetCode Premium Top Question List:

TOP GOOGLE QUESTION: [1, 85, 127, 224, 315, 329, 346, 359, 394, 444, 489, 528, 552, 560, 562, 642, 652, 659, 690, 715, 722, 727, 729, 752, 753, 767, 809, 833, 843, 844, 846, 900, 946, 951, 1031, 1048, 1060, 1110, 1138, 1153, 1231, 1293, 1296, 1345, 1376, 1423, 1438, 1463, 1477, 1548] TOP MICROSOFT QUESTION: [1, 2, 5, 8, 15, 17, 23, 25, 33, 34, 41, 42, 45, 46, 49, 53, 54, 55, 79, 85, 88, 98, 102, 103, 105, 124, 127, 138, 140, 146, 151, 155, 160, 200, 210, 212, 232, 236, 240, 273, 287, 295, 297, 340, 428, 445, 468, 545, 767, 1239] TOP FACEBOOK QUESTION: [23, 34, 56, 65, 67, 88, 124, 125, 133, 140, 158, 173, 199, 211, 215, 227, 238, 249, 269, 270, 273, 278, 282, 297, 301, 311, 339, 340, 398, 415, 438, 523, 528, 543, 560, 621, 636, 670, 680, 689, 721, 785, 938, 953, 973, 986, 987, 1026, 1249, 1428] TOP AMAZON QUESTION: [1, 5, 21, 23, 42, 49, 56, 126, 127, 138, 139, 140, 146, 185, 200, 210, 212, 227, 239, 253, 269, 273, 295, 297, 348, 353, 380, 403, 437, 460, 472, 588, 682, 692, 721, 763, 815, 819, 863, 901, 937, 957, 973, 994, 1091, 1120, 1152, 1167, 1192, 1429]

Detail Solutions

Study Group

Others

Usually online judgement TLE limitation is 1 second. => we can estimate the time complexity as the power of ten.

Quick typing math symbol

VSCode ignore formatting on file

 ! [new branch]      master     -> origin/master  (unable to update local ref)
warning: url has no scheme: 
fatal: credential url cannot be parsed:
error: update_ref failed for ref 'refs/remotes/origin/master': cannot lock ref 'refs/remotes/origin/master': unable to resolve reference 'refs/remotes/origin/master': reference broken

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My LeetCode practice source code and notes.

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