LeetCode solutions

My solutions to Leetcode Problems

• All are AC solutions
• Very few will have comments, because I wrote them for myself. But raise an issue if you want to understand more about a solution, and I will add an explanation
• There is a small chance that a handful of solutions are not mine, because I sometimes submit solutions that my students ask me to debug. Raise an issue and I will remove it

Thanks to world177/Leetcode-Downloader-for-Submissions for bulk download.

Problems by tags

Array scanning

• Apply operations to make string empty
• Count the number of special characters ii
• Dota2 senate
• Maximum enemy forts that can be captured
• Maximum value of an ordered triplet i
• Maximum value of an ordered triplet ii
• Minimum operations to maximize last elements in arrays
• Minimum right shifts to sort the array
• Monotonic array
• Number of laser beams in a bank
• Remove colored pieces if both neighbors are the same color
• Separate black and white balls
• Smallest missing integer greater than sequential prefix sum
• Sum of absolute differences in a sorted array
• The employee that worked on the longest task

Contiguous region

• Arithmetic slices
• Check if all 1s are at least length k places away
• Consecutive characters
• Count alternating subarrays
• Count binary substrings
• Count number of homogenous substrings
• Distribute candies
• Find all good indices
• Find if array can be sorted
• Find longest special substring that occurs thrice i
• Find longest special substring that occurs thrice ii
• Find the longest balanced substring of a binary string
• Invalid transactions
• Largest submatrix with rearrangements
• Length of the longest alphabetical continuous substring
• Longer contiguous segments of ones than zeros
• Longest alternating subarray
• Longest even odd subarray with threshold
• Longest mountain in array
• Longest non decreasing subarray from two arrays
• Longest subarray with maximum bitwise and
• Longest substring of all vowels in order
• Longest turbulent subarray
• Max consecutive ones
• Maximal rectangle
• Maximize area of square hole in grid
• Maximum ascending subarray sum
• Maximum product subarray
• Minimum cost to make all characters equal
• Minimum time to make rope colorful
• Number of zero filled subarrays
• Reduce array size to the half
• The number of weak characters in the game

From both ends of array

• Beautiful towers ii
• Best time to buy and sell stock iii
• Candy
• Count palindromic subsequences
• Count the number of incremovable subarrays i
• Count the number of incremovable subarrays ii
• Find all good indices
• Find the distinct difference array
• Largest plus sign
• Left and right sum differences
• Maximize distance to closest person
• Maximize win from two segments
• Maximum building height
• Minimum average difference
• Minimum cost to make all characters equal
• Minimum cost to make array equal
• Minimum index of a valid split
• Minimum number of flips to make the binary string alternating
• Minimum remove to make valid parentheses
• Minimum sum of mountain triplets i
• Minimum sum of mountain triplets ii
• Partition array into disjoint intervals
• Product of array except self
• Subsequence with the minimum score
• Sum of distances
• Take k of each character from left and right
• Unique length 3 palindromic subsequences

Element exclusion

• Construct product matrix
• Maximum or

In-place modification

• Duplicate zeros
• Find all duplicates in an array
• Merge sorted array
• Move zeroes
• Remove all adjacent duplicates in string
• Remove duplicates from sorted array
• Remove duplicates from sorted array ii
• Remove element
• Reverse vowels of a string

Location of previous element with bit value

• Minimum sum of values by dividing array

Location of previous element with same value

• Count the number of good partitions
• Count unique characters of all substrings of a given string
• Execution of all suffix instructions staying in a grid
• Largest substring between two equal characters
• Maximize the number of partitions after operations
• Number of subarrays with bounded maximum
• Number of ways to divide a long corridor
• Shortest subarray with or at least k i
• Shortest subarray with or at least k ii
• Split array into maximum number of subarrays
• Subarrays distinct element sum of squares i
• Subarrays distinct element sum of squares ii
• Substring with largest variance
• Ways to split array into good subarrays

Modify element with index

• Best sightseeing pair

Right to left

• Execution of all suffix instructions staying in a grid
• Find the original array of prefix xor
• Jump game ii
• Jump game vi
• Largest element in an array after merge operations
• Largest odd number in string
• Longest binary subsequence less than or equal to k
• Maximize the number of partitions after operations
• Minimum operations to collect elements
• Minimum operations to make a special number
• Minimum replacements to sort the array
• Plus one
• Smallest subarrays with maximum bitwise or
• Solving questions with brainpower
• The number of weak characters in the game
• Using a robot to print the lexicographically smallest string
• Visit array positions to maximize score

Averaging from total and count

• Average of levels in binary tree
• Count nodes equal to average of subtree
• Design underground system
• Find the grid of region average
• Finding mk average
• Minimum average difference

Backtracking

• All paths from source to target
• All possible full binary trees
• Beautiful arrangement
• Combination sum
• Combination sum iii
• Expression add operators
• Find the punishment number of an integer
• Generate parentheses
• Maximum number of groups getting fresh donuts
• Maximum score words formed by letters
• N queens
• Number of valid clock times
• Partition to k equal sum subsets

Minimum option optimisation

• Sudoku solver

Push and pop for efficient state update

• Combinations
• Path sum ii
• Path sum iii
• Path with maximum gold
• Reconstruct itinerary
• Word search ii

Binary lifting

• Maximize value of function in a ball passing game
• Minimum edge weight equilibrium queries in a tree
• Prison cells after n days

Binary search

• Binary search
• Capacity to ship packages within d days
• Construct binary search tree from preorder traversal
• Count subarrays with score less than k
• Data stream as disjoint intervals
• Design movie rental system
• Dungeon game
• Earliest second to mark indices i
• Earliest second to mark indices ii
• Find building where alice and bob can meet
• Find first and last position of element in sorted array
• Find in mountain array
• Find k closest elements
• Find right interval
• Find smallest letter greater than target
• Find the duplicate number
• Find the longest valid obstacle course at each position
• Find the maximum number of marked indices
• Find the smallest divisor given a threshold
• Find the sum of subsequence powers
• First bad version
• Guess number higher or lower
• H index
• H index ii
• House robber iv
• K th smallest prime fraction
• Koko eating bananas
• Kth smallest amount with single denomination combination
• Kth smallest element in a sorted matrix
• Kth smallest number in multiplication table
• Longest palindromic substring
• Longest subsequence with limited sum
• Maximize the minimum powered city
• Maximum distance between a pair of values
• Maximum number of alloys
• Maximum number of removable characters
• Maximum number of robots within budget
• Maximum running time of n computers
• Maximum tastiness of candy basket
• Maximum value at a given index in a bounded array
• Maximum xor of two numbers in an array
• Median of two sorted arrays
• Minimize maximum of array
• Minimize the maximum difference of pairs
• Minimum cost for tickets
• Minimum operations to make all array elements equal
• Minimum speed to arrive on time
• Minimum time to complete trips
• Minimum time to repair cars
• Nth magical number
• Partition array such that maximum difference is k
• Peak index in a mountain array
• Prime subtraction operation
• Split array largest sum

C++ set

• 132 pattern
• Closest room
• Contains duplicate iii
• Count of range sum
• Maximum balanced subsequence sum
• Maximum number of points from grid queries
• Maximum sum queries
• Minimum absolute difference between elements with constraint
• Minimum absolute sum difference
• Minimum reverse operations
• My calendar i
• Online majority element in subarray
• Random pick with weight
• Random point in non overlapping rectangles
• Snapshot array

Exponential-binary search

• Maximum number that sum of the prices is less than or equal to k

Prefix sum

• Delivering boxes from storage to ports
• Max sum of rectangle no larger than k
• Random pick with weight
• Random point in non overlapping rectangles

Bitwise operation

• Apply bitwise operations to make strings equal
• Apply operations on array to maximize sum of squares
• Binary watch
• Bitwise and of numbers range
• Check if a string contains all binary codes of size k
• Check if bitwise or has trailing zeros
• Cinema seat allocation
• Complement of base 10 integer
• Concatenation of consecutive binary numbers
• Count pairs with xor in a range
• Counting bits
• Cycle length queries in a tree
• Determine if string halves are alike
• Divide two integers
• Find a good subset of the matrix
• Find a value of a mysterious function closest to target
• Find if array can be sorted
• Find the k or of an array
• Find xor sum of all pairs bitwise and
• Form smallest number from two digit arrays
• Gray code
• Hamming distance
• K th symbol in grammar
• Longest uncommon subsequence ii
• Maximum length of a concatenated string with unique characters
• Maximum number of achievable transfer requests
• Maximum or
• Maximum product of word lengths
• Maximum rows covered by columns
• Maximum strength of a group
• Maximum strong pair xor i
• Maximum strong pair xor ii
• Maximum xor after operations
• Maximum xor for each query
• Minimize xor
• Minimum flips to make a or b equal to c
• Minimum impossible or
• Minimum one bit operations to make integers zero
• Minimum operations to form subsequence with target sum
• Minimum operations to make the integer zero
• Minimum operations to reduce an integer to 0
• Minimum sum of values by dividing array
• Minimum xor sum of two arrays
• Missing number
• Non decreasing subsequences
• Non negative integers without consecutive ones
• Number complement
• Number of 1 bits
• Number of even and odd bits
• Number of excellent pairs
• Number of possible sets of closing branches
• Power of four
• Power of two
• Powx n
• Prison cells after n days
• Range product queries of powers
• Remove duplicate letters
• Remove invalid parentheses
• Score after flipping matrix
• Shortest path to get all keys
• Shortest subarray with or at least k i
• Shortest subarray with or at least k ii
• Smallest subarrays with maximum bitwise or
• Smallest sufficient team
• Special permutations
• Split array into maximum number of subarrays
• String compression ii
• Sum of values at indices with k set bits
• Unique length 3 palindromic subsequences
• Utf 8 validation

Build result bit-by-bit

• Find xor beauty of array
• Maximum xor of two numbers in an array
• Minimize or of remaining elements using operations
• Minimum number of flips to convert binary matrix to zero matrix

Self-inverse property of xor

• Bitwise xor of all pairings
• Count pairs of points with distance k
• Count paths that can form a palindrome in a tree
• Count the number of beautiful subarrays
• Find the maximum sum of node values
• Find the original array of prefix xor
• Maximum xor product
• Minimum number of operations to make array xor equal to k
• Neighboring bitwise xor
• Number of wonderful substrings
• Pseudo palindromic paths in a binary tree
• Substring xor queries

Brute force enumeration

Combinatorial

• Fair distribution of cookies
• Iterator for combination
• Longest uncommon subsequence ii
• Matchsticks to square
• Maximum length of a concatenated string with unique characters
• Maximum number of achievable transfer requests
• Maximum rows covered by columns
• Maximum strength of a group
• Minimum moves to spread stones over grid
• N queens
• N queens ii
• Non decreasing subsequences
• Number of possible sets of closing branches
• Permutations
• Probability of a two boxes having the same number of distinct balls
• Remove invalid parentheses
• Shortest string that contains three strings

Elementwise processing using a vector

• Kth smallest amount with single denomination combination
• Letter case permutation
• Letter combinations of a phone number
• Minimum number of flips to convert binary matrix to zero matrix
• Numbers with same consecutive differences

Case-by-case analysis

• Make number of distinct characters equal

ChatGPT

• All possible full binary trees
• Can make arithmetic progression from sequence
• Combinations
• Design parking system
• Longest arithmetic subsequence
• Longest arithmetic subsequence of given difference
• Maximum level sum of a binary tree
• Minimum ascii delete sum for two strings
• Minimum flips to make a or b equal to c
• Minimum size subarray sum
• Number of provinces
• Peak index in a mountain array
• Predict the winner
• Stone game iii
• Strange printer
• Time needed to inform all employees

Fixed

• Frog jump
• Number of music playlists

Concurrency

• Building h2o
• Fizz buzz multithreaded
• Print foobar alternately
• Print in order
• Print zero even odd

Construction

• Beautiful arrangement ii
• Beautiful array

Counting elements in array

• 3sum with multiplicity
• Determine if two strings are close
• Find all anagrams in a string
• Intersection of two arrays ii
• Largest palindromic number
• Longest palindrome
• Minimum penalty for a shop

Deque

Monotonic deque

• Find maximum non decreasing array length
• Maximum number of robots within budget

Design data structure

• Construct quad tree
• Data stream as disjoint intervals
• Design a food rating system
• Design a number container system
• Design add and search words data structure
• Design authentication manager
• Design browser history
• Design circular queue
• Design hashmap
• Design hashset
• Design memory allocator
• Design movie rental system
• Design parking system
• Design underground system
• Encode and decode tinyurl
• Find consecutive integers from a data stream
• Frequency tracker
• Implement trie prefix tree
• Insert delete getrandom o1
• Iterator for combination
• Lfu cache
• Longest uploaded prefix
• Lru cache
• Maximum frequency stack
• Min stack
• Number of recent calls
• Online majority element in subarray
• Peeking iterator
• Random pick with weight

Interconversion

• Implement queue using stacks
• Implement stack using queues

Persistent

• Snapshot array

Disjoint set union

• Accounts merge
• Checking existence of edge length limited paths
• Find all people with secret
• Find critical and pseudo critical edges in minimum spanning tree
• Find the safest path in a grid
• Greatest common divisor traversal
• Largest component size by common factor
• Last day where you can still cross
• Lexicographically smallest equivalent string
• Maximum segment sum after removals
• Min cost to connect all points
• Minimum cost walk in weighted graph
• Number of good paths
• Number of islands
• Rank transform of a matrix
• Redundant connection
• Remove max number of edges to keep graph fully traversable
• Satisfiability of equality equations
• Similar string groups
• Sum of subarray minimums

Divide and conquer

• Reveal cards in increasing order

Dynamic programming

• Arithmetic slices ii subsequence
• Beautiful towers ii
• Best team with no conflicts
• Best time to buy and sell stock iii
• Best time to buy and sell stock with cooldown
• Binary trees with factors
• Burst balloons
• Cheapest flights within k stops
• Check if it is possible to split array
• Check if there is a valid partition for the array
• Climbing stairs
• Concatenated words
• Count number of ways to place houses
• Count palindromic subsequences
• Count square submatrices with all ones
• Count unique characters of all substrings of a given string
• Count vowels permutation
• Count ways to build good strings
• Decode ways
• Decode ways ii
• Delete and earn
• Domino and tromino tiling
• Edit distance
• Extra characters in a string
• Fibonacci number
• Find all possible stable binary arrays i
• Find all possible stable binary arrays ii
• Frog jump
• House robber
• Jump game
• Jump game ii
• Longest arithmetic subsequence
• Longest arithmetic subsequence of given difference
• Longest string chain
• Longest unequal adjacent groups subsequence i
• Maximize the number of partitions after operations
• Maximum alternating subsequence sum
• Maximum balanced subsequence sum
• Maximum deletions on a string
• Maximum number of jumps to reach the last index
• Maximum strictly increasing cells in a matrix
• Min cost climbing stairs
• Minimum cost for tickets
• Minimum cost to convert string ii
• Minimum cost to cut a stick
• Minimum cost to make all characters equal
• Minimum cost to make array equal
• Minimum cost to split an array
• Minimum difficulty of a job schedule
• Minimum increment operations to make array beautiful
• Minimum penalty for a shop
• Minimum sideway jumps
• Minimum time to remove all cars containing illegal goods
• New 21 game
• Number of distinct roll sequences
• Number of music playlists
• Number of ways to rearrange sticks with k sticks visible
• Number of ways to reorder array to get same bst
• Paint house iii
• Palindrome partitioning ii
• Palindrome partitioning iii
• Palindrome partitioning iv
• Partition array for maximum sum
• Partition string into substrings with values at most k
• Pascals triangle
• Remove boxes
• Restore ip addresses
• Restore the array
• Solving questions with brainpower
• Sorting three groups
• Soup servings
• Split array into maximum number of subarrays
• Stone game iii
• Strange printer
• The number of beautiful subsets
• Ways to express an integer as sum of powers

Array reuse

• Champagne tower
• Cherry pickup ii
• Coin change
• Coin change 2
• Decremental string concatenation
• Delete operation for two strings
• Distinct subsequences
• Find the sum of subsequence powers
• Find the sum of the power of all subsequences
• Freedom trail
• Interleaving string
• K inverse pairs array
• Knight dialer
• Length of the longest subsequence that sums to target
• Longest binary subsequence less than or equal to k
• Longest ideal subsequence
• Longest palindromic subsequence
• Make array strictly increasing
• Maximize consecutive elements in an array after modification
• Maximum length of repeated subarray
• Maximum number of points with cost
• Maximum score from performing multiplication operations
• Maximum strength of k disjoint subarrays
• Maximum value of k coins from piles
• Minimum additions to make valid string
• Minimum falling path sum
• Minimum falling path sum ii
• Minimum insertion steps to make a string palindrome
• Minimum number of coins for fruits
• Minimum number of operations to satisfy conditions
• Minimum number of refueling stops
• Minimum path cost in a grid
• Minimum path sum
• Minimum skips to arrive at meeting on time
• Minimum sum of values by dividing array
• Minimum time to make array sum at most x
• Minimum total distance traveled
• N th tribonacci number
• Number of great partitions
• Number of strings which can be rearranged to contain substring
• Number of ways of cutting a pizza
• Number of ways to earn points
• Number of ways to form a target string given a dictionary
• Number of ways to stay in the same place after some steps
• Painting the walls
• Partition equal subset sum
• Pascals triangle ii
• Paths in matrix whose sum is divisible by k
• Prison cells after n days
• String compression ii
• Tallest billboard
• Visit array positions to maximize score

Auxiliary array

• Best time to buy and sell stock iv
• Best time to buy and sell stock with transaction fee
• Count of integers
• Minimum changes to make k semi palindromes
• Minimum one bit operations to make integers zero
• Number of beautiful partitions
• Number of people aware of a secret

Binary lifting

• Maximize value of function in a ball passing game

Complexity reduction with algebra

• Power of heroes

Construction

• Find the string with lcp

Cyclic array

• Collecting chocolates
• Freedom trail
• House robber ii
• Maximum sum circular subarray
• Minimum number of flips to make the binary string alternating
• Minimum size subarray in infinite array
• Pizza with 3n slices

Digits

• Count of integers
• Count special integers
• Count stepping numbers in range
• Count the number of powerful integers
• Maximum number that sum of the prices is less than or equal to k
• Non negative integers without consecutive ones
• Number of beautiful integers in the range
• Number of digit one
• Numbers at most n given digit set

Element with special meaning

• Make array strictly increasing

Graph-like state transitions

• Knight dialer
• Knight probability in chessboard
• Maximum number of non overlapping palindrome substrings
• Minimum additions to make valid string
• Number of strings which can be rearranged to contain substring
• Number of ways to paint n 3 grid
• Special permutations

Grid

• Maximum number of moves in a grid
• Paths in matrix whose sum is divisible by k

Intervals

• Maximize the profit as the salesman
• Maximum number of events that can be attended ii
• Maximum profit in job scheduling

Knapsack

• Coin change
• Coin change 2
• Count all possible routes
• Count of sub multisets with bounded sum
• Find the sum of the power of all subsequences
• Length of the longest subsequence that sums to target
• Maximum value of k coins from piles
• Number of great partitions
• Number of ways to earn points
• Ones and zeroes
• Partition equal subset sum
• Tallest billboard

State modification

• Painting the walls

Length-wise processing

• Apply operations to make two strings equal

Longest common subsequence

• Delete operation for two strings
• Longest common subsequence
• Max dot product of two subsequences
• Maximum length of repeated subarray
• Minimum ascii delete sum for two strings

Longest increasing subsequence

• Find the longest valid obstacle course at each position
• Longest increasing subsequence
• Number of longest increasing subsequence

Matrix exponentiation

• String transformation

Memoised recursion

• Build array where you can find the maximum exactly k comparisons
• Combination sum iv
• Maximum number of operations with the same score ii
• Minimum number of days to eat n oranges
• Number of dice rolls with target sum
• Out of boundary paths
• Palindrome partitioning
• Partition string into minimum beautiful substrings
• Partition to k equal sum subsets
• Predict the winner

Monotonic stack/deque

• Find maximum non decreasing array length
• Minimum difficulty of a job schedule

Number theory

• Count the number of ideal arrays
• Largest divisible subset

Partial bottom-up

• Decremental string concatenation
• String compression ii
• Tallest billboard

Reconstructing optimal solution

• Longest unequal adjacent groups subsequence ii

Segment tree

• Count increasing quadruplets
• Delivering boxes from storage to ports

Subsets

• Construct smallest number from di string
• Count the number of square free subsets
• Find the shortest superstring
• Maximize score after n operations
• Minimum xor sum of two arrays
• Smallest sufficient team
• Special permutations

Topological sort

• Largest color value in a directed graph

Trees

• All nodes distance k in binary tree
• Count number of possible root nodes
• Count valid paths in a tree
• Cousins in binary tree ii
• Diameter of binary tree
• Difference between maximum and minimum price sum
• Employee importance
• Find duplicate subtrees
• Find number of coins to place in tree nodes
• Height of binary tree after subtree removal queries
• House robber iii
• Longest path with different adjacent characters
• Longest univalue path
• Maximum number of k divisible components
• Maximum points after collecting coins from all nodes
• Maximum score after applying operations on a tree
• Minimize the total price of the trips
• Minimum cost to change the final value of expression
• Minimum edge reversals so every node is reachable
• Minimum score after removals on a tree
• Most profitable path in a tree

DP over children

• Count pairs of connectable servers in a weighted tree network
• Find the maximum sum of node values

Dynamic update of left and right neighbours

• Robot collisions
• Sum of imbalance numbers of all subarrays

Encoding and decoding

• Encode and decode tinyurl

Flattening

• Flatten a multilevel doubly linked list
• Flatten binary tree to linked list
• Flatten nested list iterator

Formatted output

• Binary watch
• Integer to english words
• Integer to roman

Graph theory

• Maximal network rank

Addition of auxiliary vertices

• Greatest common divisor traversal
• Shortest path to get all keys

Bipartite graph

• Divide nodes into the maximum number of groups

Breadth first search

• 01 matrix
• Amount of time for binary tree to be infected
• As far from land as possible
• Bus routes
• Detonate the maximum bombs
• Divide nodes into the maximum number of groups
• Find the safest path in a grid
• Jump game iv
• Maximum level sum of a binary tree
• Minimum genetic mutation
• Minimum moves to capture the queen
• Minimum number of visited cells in a grid
• Minimum operations to convert number
• Minimum reverse operations
• Nearest exit from entrance in maze
• Open the lock
• Pacific atlantic water flow
• Shortest bridge
• Shortest path to get all keys
• Shortest path with alternating colors
• Special permutations

Bridges/Articulation points

• Critical connections in a network

Cycle detection

• Find closest node to given two nodes
• Happy number

Degree counting

• Add edges to make degrees of all nodes even
• Collect coins in a tree
• Find champion i
• Find champion ii
• Find the town judge
• Minimum number of vertices to reach all nodes
• Restore the array from adjacent pairs
• Validate binary tree nodes

Depth first search

• Amount of time for binary tree to be infected
• Count number of possible root nodes
• Count pairs of connectable servers in a weighted tree network
• Count paths that can form a palindrome in a tree
• Count valid paths in a tree
• Create components with same value
• Critical connections in a network
• Delete nodes and return forest
• Detect cycles in 2d grid
• Difference between maximum and minimum price sum
• Employee importance
• Find if path exists in graph
• Find number of coins to place in tree nodes
• Find the maximum sum of node values
• Jump game iii
• Keys and rooms
• Longest increasing path in a matrix
• Longest path with different adjacent characters
• Maximum number of k divisible components
• Maximum points after collecting coins from all nodes
• Maximum score after applying operations on a tree
• Minimize the total price of the trips
• Minimum edge reversals so every node is reachable
• Minimum edge weight equilibrium queries in a tree
• Minimum fuel cost to report to the capital
• Minimum number of operations to sort a binary tree by level
• Minimum score after removals on a tree
• Minimum score of a path between two cities
• Minimum time to collect all apples in a tree
• Most profitable path in a tree
• Number of increasing paths in a grid
• Number of nodes in the sub tree with the same label
• Reachable nodes with restrictions
• Reorder routes to make all paths lead to the city zero
• Shortest cycle in a graph
• Time needed to inform all employees
• Validate binary tree nodes

Colouring

• Is graph bipartite
• Possible bipartition

Component decomposition

• Count the number of complete components
• Count unreachable pairs of nodes in an undirected graph
• Divide nodes into the maximum number of groups
• Evaluate division
• Most stones removed with same row or column
• Number of islands
• Number of operations to make network connected
• Number of provinces

Flood fill

• Count sub islands
• Flood fill
• Making a large island
• Max area of island
• Maximum number of fish in a grid
• Number of closed islands
• Number of enclaves
• Shortest bridge

Iterative

• Find eventual safe states

Tree diameter

• Minimum height trees

Dijkstra's algorithm

• Design graph with shortest path calculator
• Minimum cost of a path with special roads
• Minimum time to visit a cell in a grid
• Minimum time to visit disappearing nodes
• Modify graph edge weights
• Network delay time
• Number of ways to arrive at destination
• Path with maximum probability
• Path with minimum effort
• Reachable nodes in subdivided graph

Forward and backward

• Find edges in shortest paths

Directed acyclic graph

• All paths from source to target
• Find champion i
• Find champion ii

Floyd-Warshall algorithm

• Minimum cost to convert string i
• Minimum cost to convert string ii
• Number of possible sets of closing branches

Iterative leaf removal

• Collect coins in a tree

Lewel-wise processing

• Maximum strictly increasing cells in a matrix

Lowest common ancestor

• Minimum edge weight equilibrium queries in a tree

Minimum spanning tree

• Find critical and pseudo critical edges in minimum spanning tree
• Min cost to connect all points

Multi source search

• As far from land as possible
• Find the safest path in a grid
• Shortest bridge
• Shortest path with alternating colors

Prim's algorithm

• Maximum number of points from grid queries

Reuse visited array

• Divide nodes into the maximum number of groups
• Shortest cycle in a graph

Single cycle graphs

• Count the number of houses at a certain distance i
• Count the number of houses at a certain distance ii

Single outdegree graphs

• Count visited nodes in a directed graph
• Destination city
• Find closest node to given two nodes
• Longest cycle in a graph
• Node with highest edge score
• Where will the ball fall

Topological sort

• Build a matrix with conditions
• Course schedule
• Course schedule ii
• Find eventual safe states
• Maximum strictly increasing cells in a matrix

Dynamic Programming

• Largest color value in a directed graph
• Parallel courses iii

Greedy

• Advantage shuffle
• Append characters to string to make subsequence
• Apple redistribution into boxes
• Apply operations on array to maximize sum of squares
• Apply operations to make all array elements equal to zero
• Apply operations to maximize score
• Assign cookies
• Bag of tokens
• Best time to buy and sell stock ii
• Boats to save people
• Candy
• Course schedule iii
• Determine the minimum sum of a k avoiding array
• Divide array into arrays with max difference
• Dota2 senate
• Earliest possible day of full bloom
• Earliest second to mark indices i
• Earliest second to mark indices ii
• Eliminate maximum number of monsters
• Find polygon with the largest perimeter
• Find the maximum number of marked indices
• Find the minimum possible sum of a beautiful array
• Find the value of the partition
• Frog jump ii
• Furthest building you can reach
• Furthest point from origin
• Gas station
• Happy students
• Is subsequence
• Largest number
• Least number of unique integers after k removals
• Lexicographically smallest string after operations with constraint
• Lexicographically smallest string after substring operation
• Longest subsequence with limited sum
• Make array zero by subtracting equal amounts
• Make costs of paths equal in a binary tree
• Make string a subsequence using cyclic increments
• Maximize greatness of an array
• Maximize happiness of selected children
• Maximize the minimum powered city
• Maximum bags with full capacity of rocks
• Maximum element after decreasing and rearranging
• Maximum ice cream bars
• Maximum length of pair chain
• Maximum matching of players with trainer
• Maximum number of coins you can get
• Maximum number of consecutive values you can make
• Maximum number of groups entering a competition
• Maximum number of groups with increasing length
• Maximum number of integers to choose from a range i
• Maximum odd binary number
• Maximum palindromes after operations
• Maximum performance of a team
• Maximum product difference between two pairs
• Maximum product of two elements in an array
• Maximum spending after buying items
• Maximum tastiness of candy basket
• Maximum units on a truck
• Maximum value after insertion
• Maximum xor product
• Mice and cheese
• Minimize maximum pair sum in array
• Minimize the maximum difference of pairs
• Minimum amount of time to fill cups
• Minimum array length after pair removals
• Minimum cost to make array equal
• Minimum deletions to make string k special
• Minimum equal sum of two arrays after replacing zeros
• Minimum levels to gain more points
• Minimum money required before transactions
• Minimum number of arrows to burst balloons
• Minimum number of changes to make binary string beautiful
• Minimum number of coins to be added
• Minimum number of groups to create a valid assignment
• Minimum number of increments on subarrays to form a target array
• Minimum number of operations to make all array elements equal to 1
• Minimum number of operations to make arrays similar
• Minimum number of pushes to type word i
• Minimum number of pushes to type word ii
• Minimum number of taps to open to water a garden
• Minimum operations to make a special number
• Minimum operations to make array equal ii
• Minimum operations to make median of array equal to k
• Minimum operations to make the array increasing
• Minimum processing time
• Minimum rectangles to cover points
• Minimum replacements to sort the array
• Minimum score by changing two elements
• Minimum sum of squared difference
• Minimum time to complete all tasks
• Minimum time to make array sum at most x
• Minimum total cost to make arrays unequal
• Minimum total distance traveled
• Non overlapping intervals
• Number of matching subsequences
• Partition labels
• Patching array
• Prime subtraction operation
• Put marbles in bags
• Queue reconstruction by height
• Rearrange array to maximize prefix score
• Rearranging fruits
• Reduce array size to the half
• Reducing dishes
• Remove adjacent almost equal characters
• Remove duplicate letters
• Remove k digits
• Remove stones to minimize the total
• Reorganize string
• Replace question marks in string to minimize its value
• Score after flipping matrix
• Smallest missing non negative integer after operations
• Split array largest sum
• Split with minimum sum

Hashmap

• Array of doubled pairs
• Binary subarrays with sum
• Brick wall
• Check array formation through concatenation
• Check distances between same letters
• Cinema seat allocation
• Clone graph
• Contains duplicate ii
• Contiguous array
• Continuous subarray sum
• Convert an array into a 2d array with conditions
• Count anagrams
• Count beautiful substrings i
• Count beautiful substrings ii
• Count complete subarrays in an array
• Count number of bad pairs
• Count number of distinct integers after reverse operations
• Count pairs of points with distance k
• Count pairs of similar strings
• Count subarrays with median k
• Count the number of beautiful subarrays
• Count the number of good subarrays
• Count the number of special characters ii
• Delete and earn
• Design hashmap
• Destroy sequential targets
• Determine if two strings are close
• Difference of number of distinct values on diagonals
• Distinct prime factors of product of array
• Encode and decode tinyurl
• Equal row and column pairs
• Evaluate the bracket pairs of a string
• Extra characters in a string
• Find duplicate file in system
• Find longest special substring that occurs thrice i
• Find longest special substring that occurs thrice ii
• Find maximum number of string pairs
• Find missing and repeated values
• Find mode in binary search tree
• Find players with zero or one losses
• Find subarrays with equal sum
• Find the difference of two arrays
• Find the distinct difference array
• Find the length of the longest common prefix
• Find the prefix common array of two arrays
• Find words that can be formed by characters
• Finding the users active minutes
• First completely painted row or column
• First letter to appear twice
• First unique character in a string
• Greatest english letter in upper and lower case
• Group anagrams
• Intersection of two arrays
• Intersection of two arrays ii
• Invalid transactions
• Jewels and stones
• K diff pairs in an array
• Largest positive integer that exists with its negative
• Length of longest subarray with at most k frequency
• Longest arithmetic subsequence of given difference
• Longest consecutive sequence
• Longest nice subarray
• Longest palindrome by concatenating two letter words
• Longest square streak in an array
• Longest uploaded prefix
• Longest word in dictionary
• Lru cache
• Make number of distinct characters equal
• Map sum pairs
• Max number of k sum pairs
• Max points on a line
• Max sum of a pair with equal sum of digits
• Maximum good subarray sum
• Maximum number of integers to choose from a range i
• Maximum number of pairs in array
• Maximum population year
• Maximum square area by removing fences from a field
• Maximum sum of distinct subarrays with length k
• Merge similar items
• Minimize string length
• Minimum amount of time to collect garbage
• Minimum array length after pair removals
• Minimum cost to convert string ii
• Minimum cost to split an array
• Minimum deletions to make character frequencies unique
• Minimum number of operations to make array empty
• Minimum number of steps to make two strings anagram
• Minimum operations to collect elements
• Minimum rounds to complete all tasks
• Minimum total cost to make arrays unequal
• Most frequent even element
• Most popular video creator
• Number of atoms
• Number of black blocks
• Number of distinct averages
• Number of excellent pairs
• Number of good pairs
• Number of nodes in the sub tree with the same label
• Number of wonderful substrings
• Odd string difference
• Optimal partition of string
• Pairs of songs with total durations divisible by 60
• Partition labels
• Path crossing
• Path sum iii
• Permutation in string
• Powerful integers
• Prefix and suffix search
• Rabbits in forest
• Ransom note
• Rearranging fruits
• Reconstruct original digits from english
• Redistribute characters to make all strings equal
• Reduce array size to the half
• Relocate marbles
• Remove zero sum consecutive nodes from linked list
• Reward top k students
• Shortest uncommon substring in an array
• Sliding subarray beauty
• Smallest subarrays with maximum bitwise or
• Subarray sums divisible by k
• Substring xor queries
• Sum of distances
• Sum of matrix after queries
• Sum of prefix scores of strings
• Take k of each character from left and right

Coordinate compression

• Design underground system
• Distribute elements into two arrays ii

Counter

• Apply operations to make string empty
• Count elements with maximum frequency
• Count substrings starting and ending with given character
• Find the maximum number of elements in subset
• Least number of unique integers after k removals
• Maximum length substring with two occurrences
• Maximum palindromes after operations
• Minimize length of array using operations
• Minimum deletions to make string k special
• Minimum levels to gain more points
• Minimum number of operations to satisfy conditions
• Minimum number of pushes to type word i
• Minimum number of pushes to type word ii
• Minimum operations to write the letter y on a grid
• Number of students unable to eat lunch
• Replace question marks in string to minimize its value
• Split the array
• Subarrays with k different integers
• Unique number of occurrences

Forward and backward

• Find and replace pattern
• Find the longest equal subarray
• First unique number
• Frequency tracker
• Insert delete getrandom o1
• Isomorphic strings
• Most frequent ids

Group items

• Find the longest equal subarray
• Group the people given the group size they belong to
• Jump game iv
• Max pair sum in an array
• Minimum seconds to equalize a circular array
• Number of good paths
• Remove letter to equalize frequency

Update using insert and delete

• Finding pairs with a certain sum
• Fraction to recurring decimal

Heuristic optimisation

• Maximum number of groups getting fresh donuts

Integer operations on strings

• Add binary
• Add two numbers
• Add two numbers ii
• Complex number multiplication
• Plus one

Intervals

• Insert interval
• Length of the longest valid substring
• Maximum number of events that can be attended
• Minimum number of taps to open to water a garden

2D

• Rectangle area ii

Dynamic Programming

• Maximize the profit as the salesman

Dynamic programming

With binary search

• Maximum number of events that can be attended ii
• Maximum profit in job scheduling

Endpoint sorting

• Car pooling
• Divide intervals into minimum number of groups
• Minimum interval to include each query
• My calendar iii
• Number of flowers in full bloom
• Rectangle area ii

Non-overlapping decomposition

• Falling squares
• Rectangle area ii

Overlap

• Count days spent together
• Count ways to group overlapping ranges
• Determine if two events have conflict
• Divide intervals into minimum number of groups
• Find the largest area of square inside two rectangles
• Interval list intersections
• Minimum time to complete all tasks
• My calendar iii
• Non overlapping intervals
• Number of flowers in full bloom
• Palindrome rearrangement queries
• Remove covered intervals
• Split the array to make coprime products

Union

• Data stream as disjoint intervals
• Merge intervals

Linked list

Iteration

• Add two numbers
• Add two numbers ii
• Convert binary number in a linked list to integer
• Convert sorted list to binary search tree
• Copy list with random pointer
• Delete node in a linked list
• Flatten a multilevel doubly linked list
• Flatten binary tree to linked list
• Insert greatest common divisors in linked list
• Insertion sort list
• Intersection of two linked lists
• Linked list random node
• Merge in between linked lists
• Merge k sorted lists
• Merge two sorted lists
• Odd even linked list
• Partition list
• Reorder list

Slow and fast pointers

• Delete the middle node of a linked list
• Linked list cycle
• Linked list cycle ii
• Maximum twin sum of a linked list
• Middle of the linked list
• Remove nth node from end of list

Recursion

• Double a number represented as a linked list
• Flatten a multilevel doubly linked list
• Maximum twin sum of a linked list
• Palindrome linked list
• Remove duplicates from sorted list ii
• Remove linked list elements
• Remove nodes from linked list
• Remove zero sum consecutive nodes from linked list

Majority element

• Majority element
• Majority element ii
• Minimum index of a valid split

Mathematics

• Maximum number of consecutive values you can make

Advanced

• Best position for a service centre

Basic

• Alice and bob playing flower game
• Angle between hands of a clock
• Apply operations to make sum of array greater than or equal to k
• Can make arithmetic progression from sequence
• Construct the longest new string
• Count of matches in tournament
• Distribute money to maximum children
• Find the maximum achievable number
• Fraction to recurring decimal
• Largest perimeter triangle
• Minimum number of operations to make array empty
• Poor pigs
• Replace question marks in string to minimize its value
• Strictly palindromic number
• Sum of absolute differences in a sorted array

Closed form expressions

• Calculate money in leetcode bank
• Count anagrams
• Count substrings starting and ending with given character
• Count total number of colored cells
• Distribute candies among children i
• Distribute candies among children ii
• Find the pivot integer
• Maximum sum with exactly k elements
• Maximum value at a given index in a bounded array
• Minimum operations to make array equal
• Power of heroes

Combinatorics

• 3sum with multiplicity
• Arithmetic slices ii subsequence
• Binary trees with factors
• Build array where you can find the maximum exactly k comparisons
• Count all possible routes
• Count all valid pickup and delivery options
• Count anagrams
• Count beautiful substrings i
• Count beautiful substrings ii
• Count collisions of monkeys on a polygon
• Count good numbers
• Count k subsequences of a string with maximum beauty
• Count nice pairs in an array
• Count number of bad pairs
• Count number of homogenous substrings
• Count number of ways to place houses
• Count pairs of nodes
• Count pairs of similar strings
• Count sorted vowel strings
• Count special integers
• Count substrings starting and ending with given character
• Count the number of fair pairs
• Count the number of good partitions
• Count the number of houses at a certain distance i
• Count the number of houses at a certain distance ii
• Count the number of ideal arrays
• Count the number of infection sequences
• Count unreachable pairs of nodes in an undirected graph
• Count ways to group overlapping ranges
• Domino and tromino tiling
• Find the sum of the power of all subsequences
• Find xor beauty of array
• Iterator for combination
• Maximum number of groups with increasing length
• Minimum number of operations to make string sorted
• Naming a company
• Number of good paths
• Number of music playlists
• Number of strings which can be rearranged to contain substring
• Number of subsequences that satisfy the given sum condition
• Number of ways to divide a long corridor
• Number of ways to reach a position after exactly k steps
• Number of ways to rearrange sticks with k sticks visible
• Number of ways to reorder array to get same bst
• Permutation sequence
• Power of heroes
• Probability of a two boxes having the same number of distinct balls
• Right triangles
• The number of beautiful subsets
• Ways to split array into good subarrays

Inclusion-exclusion

• Count increasing quadruplets
• Distribute candies among children i
• Distribute candies among children ii
• Find all possible stable binary arrays i
• Find all possible stable binary arrays ii
• Find the sum of subsequence powers
• Kth smallest amount with single denomination combination

Composition of operations

• Bitwise xor of all pairings
• Fancy sequence
• Find xor sum of all pairs bitwise and
• Handling sum queries after update

Expression rearrangement

• Find maximum non decreasing array length
• Maximum balanced subsequence sum
• Number of pairs satisfying inequality

Geometry

• Check if it is a straight line
• Determine if a cell is reachable at a given time
• Max points on a line
• Maximum area of longest diagonal rectangle
• Minimize manhattan distances
• Minimum cuts to divide a circle
• Rectangle area
• Type of triangle ii

Convex hull

• Erect the fence

Geometric median

• Best position for a service centre
• Minimum cost to make array equal

Invariants

• Minimum operations to make array equal ii

Median

• Apply operations to maximize frequency score
• Minimum cost to make array equalindromic
• Minimum operations to make median of array equal to k

Number theory

Basic

• Add digits
• Bulb switcher
• Check if it is a good array
• Check if point is reachable
• Continuous subarray sum
• Count beautiful substrings i
• Count beautiful substrings ii
• Count distinct numbers on board
• Count of interesting subarrays
• Count pairs of connectable servers in a weighted tree network
• Destroy sequential targets
• Excel sheet column title
• Factorial trailing zeroes
• Find the divisibility array of a string
• Find the student that will replace the chalk
• Greatest common divisor of strings
• Integer break
• Make k subarray sums equal
• Maximum element sum of a complete subset of indices
• Maximum number of k divisible components
• Maximum prime difference
• Minimize length of array using operations
• Minimize the maximum of two arrays
• Minimum cost to move chips to the same position
• Minimum deletions to make array divisible
• Minimum number of groups to create a valid assignment
• Minimum number of operations to make all array elements equal to 1
• Minimum rounds to complete all tasks
• Mirror reflection
• Most frequent prime
• Nth magical number
• Number of common factors
• Number of subarrays with gcd equal to k
• Number of subarrays with lcm equal to k
• Prime in diagonal
• Range product queries of powers
• Smallest missing non negative integer after operations
• Subarray sums divisible by k
• Sum multiples
• The number of beautiful subsets

Dynamic programming

• Count the number of square free subsets
• Largest divisible subset

Factor listing in sqrt(N)

• Create components with same value
• Largest divisible subset
• Smallest value after replacing with sum of prime factors

Inclusion-exclusion

• Kth smallest amount with single denomination combination

Modular exponentiation/inverse

• Apply operations to maximize score
• Count anagrams
• Count collisions of monkeys on a polygon
• Count good numbers
• Count the number of ideal arrays
• Count the number of infection sequences
• Double modular exponentiation
• Maximize number of nice divisors
• Minimum number of operations to make string sorted
• Number of subsequences that satisfy the given sum condition
• String transformation

Prime sieving

• Apply operations to maximize score
• Closest prime numbers in range
• Count primes
• Count the number of ideal arrays
• Count valid paths in a tree
• Distinct prime factors of product of array
• Greatest common divisor traversal
• Largest component size by common factor
• Maximum element sum of a complete subset of indices
• Minimum changes to make k semi palindromes
• Number of different subsequences gcds
• Prime pairs with target sum
• Prime subtraction operation
• Split the array to make coprime products

Theorems

• Perfect squares

Parity

• Minimum reverse operations

Physics observation

• Last moment before all ants fall out of a plank

Probability

• Generate random point in a circle
• Implement rand10 using rand7
• Insert delete getrandom o1
• Knight probability in chessboard
• Linked list random node
• New 21 game
• Probability of a two boxes having the same number of distinct balls
• Random pick with weight
• Random point in non overlapping rectangles
• Soup servings

Reduce problem dimension with proofs

• Find a good subset of the matrix
• Soup servings

Set theory

• Find unique binary string
• Maximum size of a set after removals

Matrix

• Difference between ones and zeros in row and column
• Difference of number of distinct values on diagonals
• Find all groups of farmland
• Find the grid of region average
• Increment submatrices by one
• Largest submatrix with rearrangements
• Maximum strictly increasing cells in a matrix
• Modify the matrix
• Right triangles

Geometric transformation

• Determine whether matrix can be obtained by rotation
• Equal row and column pairs
• Image overlap

Path

• Disconnect path in a binary matrix by at most one flip
• Dungeon game
• Last day where you can still cross
• Longest increasing path in a matrix
• Maximum number of moves in a grid
• Minimum falling path sum
• Minimum falling path sum ii
• Minimum path sum
• Most frequent prime
• Path with maximum gold
• Paths in matrix whose sum is divisible by k
• Where will the ball fall

Prefix

• Construct product matrix

Row pair processing

• Max sum of rectangle no larger than k
• Number of submatrices that sum to target

Traversal

• Count negative numbers in a sorted matrix
• Diagonal traverse
• Get biggest three rhombus sums in a grid

Meet in the middle

• 4sum
• 4sum ii
• Matchsticks to square
• Words within two edits of dictionary

Number transformations based on mathematical rules

• Minimum addition to make integer beautiful
• Minimum number of operations to make x and y equal
• Minimum operations to reduce an integer to 0
• Reach a number

Offline query processing

• Checking existence of edge length limited paths
• Find building where alice and bob can meet
• Maximum sum queries
• Minimum absolute difference queries

Palindrome

• Break a palindrome
• Count palindromic subsequences
• Count paths that can form a palindrome in a tree
• Find first palindromic string in the array
• Largest palindromic number
• Lexicographically smallest beautiful string
• Lexicographically smallest palindrome
• Longest palindrome
• Longest palindrome by concatenating two letter words
• Maximum number of non overlapping palindrome substrings
• Maximum palindromes after operations
• Minimum changes to make k semi palindromes
• Minimum cost to make array equalindromic
• Minimum insertion steps to make a string palindrome
• Number of wonderful substrings
• Palindrome linked list
• Palindrome partitioning
• Palindrome partitioning ii
• Palindrome partitioning iii
• Palindrome partitioning iv
• Palindrome rearrangement queries
• Palindromic substrings
• Remove palindromic subsequences
• Unique length 3 palindromic subsequences

Hashing

• Longest palindromic substring
• Palindrome pairs

Permutation

• Permutation sequence

Cycle

• Array nesting
• Minimum number of operations to reinitialize a permutation
• Minimum number of operations to sort a binary tree by level

Inverse

• Build a matrix with conditions
• Build array from permutation
• Relative ranks

Inversions

• Global and local inversions
• Minimum adjacent swaps to reach the kth smallest number

Next/Previous

• Minimum adjacent swaps to reach the kth smallest number
• Minimum number of operations to make string sorted
• Next greater element iii
• Next permutation
• Permutations ii

Swaps

• Check if strings can be made equal with operations ii
• Make lexicographically smallest array by swapping elements
• Orderly queue
• Semi ordered permutation

Pointers

• Clone graph
• Copy list with random pointer

Points in 2D plane

• Find the number of ways to place people i
• Find the number of ways to place people ii

Precomputation to answer queries efficiently with delta

• Number of adjacent elements with the same color
• Sum of even numbers after queries

Prefix

Bitwise operation

• Maximum or
• Number of wonderful substrings
• Unique length 3 palindromic subsequences

Extremum

• 132 pattern
• Best sightseeing pair
• Best time to buy and sell stock
• Best time to buy and sell stock iii
• Count subarrays with fixed bounds
• Find the score of all prefixes of an array
• Global and local inversions
• Increasing triplet subsequence
• Partition array into disjoint intervals
• Using a robot to print the lexicographically smallest string

Sum

• Apply operations to maximize frequency score
• Binary subarrays with sum
• Contiguous array
• Continuous subarray sum
• Count beautiful substrings i
• Count beautiful substrings ii
• Count complete substrings
• Count days spent together
• Count of interesting subarrays
• Count subarrays where max element appears at least k times
• Count subarrays with median k
• Count subarrays with score less than k
• Count tested devices after test operations
• Count vowel strings in ranges
• Delivering boxes from storage to ports
• Execution of all suffix instructions staying in a grid
• Find maximum non decreasing array length
• Find the highest altitude
• Find the score of all prefixes of an array
• Find the substring with maximum cost
• Gas station
• Left and right sum differences
• Longest subsequence with limited sum
• Longest valid parentheses
• Max sum of rectangle no larger than k
• Maximal rectangle
• Maximum good subarray sum
• Maximum nesting depth of two valid parentheses strings
• Maximum product subarray
• Maximum score of spliced array
• Maximum subarray
• Maximum subarray min product
• Maximum sum circular subarray
• Maximum xor for each query
• Minimum absolute difference queries
• Minimum amount of time to collect garbage
• Minimum cost to make all characters equal
• Minimum edge weight equilibrium queries in a tree
• Minimum moves to pick k ones
• Minimum operations to make all array elements equal
• Minimum size subarray in infinite array
• Minimum space wasted from packaging
• Minimum value to get positive step by step sum
• Movement of robots
• Palindrome rearrangement queries
• Random pick with weight
• Random point in non overlapping rectangles
• Range sum query immutable
• Reducing dishes
• Remove zero sum consecutive nodes from linked list
• Subarray sums divisible by k
• Substring with largest variance
• Sum of absolute differences in a sorted array

2D

• Construct product matrix
• Construct quad tree
• Count submatrices with top left element and sum less than k
• Disconnect path in a binary matrix by at most one flip
• Increment submatrices by one
• Maximal square
• Number of submatrices that sum to target
• Number of ways of cutting a pizza
• Range sum query 2d immutable

For range updates

• Apply operations to make all array elements equal to zero
• Count the number of good partitions
• Count the number of houses at a certain distance i
• Count the number of houses at a certain distance ii
• Increment submatrices by one
• Invalid transactions
• Maximize the minimum powered city

Valid brackets

• Maximum nesting depth of the parentheses
• Minimum remove to make valid parentheses
• Remove invalid parentheses

Priority queue

• Constrained subsequence sum
• Earliest second to mark indices ii
• Find original array from doubled array
• First unique character in a string
• Furthest building you can reach
• Ipo
• Jump game vi
• Last stone weight
• Length of the longest valid substring
• Maximal score after applying k operations
• Maximum frequency stack
• Maximum number of events that can be attended
• Maximum number of points from grid queries
• Maximum spending after buying items
• Meeting rooms iii
• Merge k sorted lists
• Minimize deviation in array
• Minimum interval to include each query
• Minimum operations to exceed threshold value ii
• Minimum operations to form subsequence with target sum
• Number of orders in the backlog
• Parallel courses iii
• Process tasks using servers
• Remove stones to minimize the total
• Reorganize string
• Robot collisions
• Sort an array
• Time to cross a bridge
• Total cost to hire k workers

Dijkstra's algorithm

• Design graph with shortest path calculator
• Minimum cost of a path with special roads
• Minimum time to visit a cell in a grid
• Modify graph edge weights
• Network delay time

Dijkstra-like processing of subarrays

• Find the k sum of an array

Dynamic sorted neighbour

• Sum of imbalance numbers of all subarrays

K smallest/largest elements

• Find k pairs with smallest sums
• Find the most competitive subsequence
• Get biggest three rhombus sums in a grid
• Kth largest element in a stream
• Lfu cache
• Maximum elegance of a k length subsequence
• Maximum performance of a team
• Maximum subsequence score
• Minimum cost to hire k workers

Transfer between the two

• Divide an array into subarrays with minimum cost i
• Divide an array into subarrays with minimum cost ii
• Find median from data stream
• Finding mk average

Key update using insert and remove on C++ set

• Count zero request servers
• Design a food rating system
• Design a number container system
• Design authentication manager
• Design graph with shortest path calculator
• Find edges in shortest paths
• Lfu cache
• Lru cache
• Minimum cost of a path with special roads
• Minimum time to visit a cell in a grid
• Minimum time to visit disappearing nodes
• Modify graph edge weights
• Network delay time
• Number of ways to arrive at destination
• Path with maximum probability
• Reachable nodes in subdivided graph
• Take gifts from the richest pile

Process in unusual order

• Reconstruct original digits from english

Process multiple vectors together

• Number of matching subsequences

QuadTree

• Construct quad tree

Queue

• Number of recent calls

Quick Select

• Kth largest element in an array
• Minimum moves to equal array elements ii

Range updates using prefix sum

• Invalid transactions

Search by iterative bound improvement

• Minimize the maximum of two arrays

Segment tree

• Count increasing quadruplets
• Count of range sum
• Count of smaller numbers after self
• Count pairs with xor in a range
• Create sorted array through instructions
• Delivering boxes from storage to ports
• Distribute elements into two arrays ii
• Fancy sequence
• Jump game vii
• Longest increasing subsequence ii
• Make array empty
• Minimum sum of values by dividing array
• Next greater element iv
• Number of pairs satisfying inequality
• Range sum query mutable

Lazy propagation

• Handling sum queries after update
• Subarrays distinct element sum of squares i
• Subarrays distinct element sum of squares ii

Simple implementation

• Account balance after rounded purchase
• Add to array form of integer
• Alternating digit sum
• Ant on the boundary
• Apply operations to an array
• Arithmetic subarrays
• Arranging coins
• Average salary excluding the minimum and maximum salary
• Average value of even numbers that are divisible by three
• Beautiful towers i
• Best poker hand
• Bulls and cows
• Calculate amount paid in taxes
• Calculate delayed arrival time
• Can place flowers
• Categorize box according to criteria
• Check distances between same letters
• Check if a string contains all binary codes of size k
• Check if a string is an acronym of words
• Check if all the integers in a range are covered
• Check if matrix is x matrix
• Check if number is a sum of powers of three
• Check if strings can be made equal with operations i
• Check if the sentence is pangram
• Check if two string arrays are equivalent
• Check if word equals summation of two words
• Check knight tour configuration
• Convert the temperature
• Count and say
• Count asterisks
• Count number of distinct integers after reverse operations
• Count odd numbers in an interval range
• Count pairs whose sum is less than target
• Count symmetric integers
• Count the digits that divide a number
• Count the number of special characters i
• Count the number of vowel strings in range
• Delete columns to make sorted
• Determine color of a chessboard square
• Determine if string halves are alike
• Determine the winner of a bowling game
• Difference between element sum and digit sum of an array
• Difference between ones and zeros in row and column
• Distribute candies
• Distribute candies to people
• Distribute elements into two arrays i
• Divisible and non divisible sums difference
• Duplicate zeros
• Excel sheet column number
• Existence of a substring in a string and its reverse
• Faulty keyboard
• Find common elements between two arrays
• Find first palindromic string in the array
• Find nearest point that has the same x or y coordinate
• Find numbers with even number of digits
• Find subarrays with equal sum
• Find the array concatenation value
• Find the distance value between two arrays
• Find the losers of the circular game
• Find the maximum divisibility score
• Find the peaks
• Find the pivot integer
• Find the sum of encrypted integers
• Find the town judge
• Find the width of columns of a grid
• Find the winner of an array game
• Find the winner of the circular game
• Find winner on a tic tac toe game
• Find words containing character
• Fizz buzz
• Flipping an image
• Game of life
• Get biggest three rhombus sums in a grid
• Get maximum in generated array
• Greatest english letter in upper and lower case
• Harshad number
• How many numbers are smaller than the current number
• Image overlap
• Image smoother
• Incremental memory leak
• Integer replacement
• Island perimeter
• K items with the maximum sum
• Kids with the greatest number of candies
• Largest 3 same digit number in string
• Largest local values in a matrix
• Largest magic square
• Largest positive integer that exists with its negative
• Largest time for given digits
• Last visited integers
• Latest time you can obtain after replacing characters
• Longest strictly increasing or strictly decreasing subarray
• Make three strings equal
• Match substring after replacement
• Matrix diagonal sum
• Matrix similarity after cyclic shifts
• Maximum 69 number
• Maximum count of positive integer and negative integer
• Maximum difference by remapping a digit
• Maximum number of balloons
• Maximum number of operations with the same score i
• Maximum number of pairs in array
• Maximum score after splitting a string
• Maximum star sum of a graph
• Maximum sum of an hourglass
• Maximum value of a string in an array
• Merge strings alternately
• Merge triplets to form target triplet
• Min max game
• Minimum amount of time to fill cups
• Minimum changes to make alternating binary string
• Minimum distance to the target element
• Minimum domino rotations for equal row
• Minimum hours of training to win a competition
• Minimum number game
• Minimum number of swaps to make the binary string alternating
• Minimum operations to exceed threshold value i
• Minimum time visiting all points
• Modify the matrix
• Most frequent even element
• Next greater element i
• Non decreasing array
• Number of arithmetic triplets
• Number of beautiful pairs
• Number of changing keys
• Number of employees who met the target
• Number of senior citizens
• Number of steps to reduce a number to zero
• Number of unequal triplets in array
• Odd string difference
• Palindrome number
• Pancake sorting
• Partitioning into minimum number of deci binary numbers
• Pass the pillow
• Perform string shifts
• Points that intersect with cars
• Power of three
• Powerful integers
• Push dominoes
• Queries on number of points inside a circle
• Range addition ii
• Remove all occurrences of a substring
• Remove one element to make the array strictly increasing
• Remove palindromic subsequences
• Remove trailing zeros from a string
• Reverse prefix of word
• Row with maximum ones
• Score of a string
• Separate the digits in an array
• Shortest and lexicographically smallest beautiful string
• Shortest distance to target string in a circular array
• Shuffle the array
• Smallest even multiple
• Sort vowels in a string
• Special positions in a binary matrix
• Sum of number and its reverse
• Sum of squares of special elements
• The employee that worked on the longest task
• Time needed to buy tickets
• Toeplitz matrix
• Total distance traveled
• Ugly number
• Water bottles ii
• Zigzag conversion

Simple implementation0

• Make a square with the same color

Sliding window

• 3sum
• 3sum closest
• Apply operations to maximize frequency score
• Binary trees with factors
• Constrained subsequence sum
• Contains duplicate ii
• Continuous subarrays
• Count pairs of nodes
• Count the number of fair pairs
• Count the number of good subarrays
• Count the number of incremovable subarrays i
• Count the number of incremovable subarrays ii
• Divide an array into subarrays with minimum cost i
• Divide an array into subarrays with minimum cost ii
• Find a value of a mysterious function closest to target
• Find all anagrams in a string
• Find the longest equal subarray
• Frequency of the most frequent element
• Fruit into baskets
• Invalid transactions
• K radius subarray averages
• K th smallest prime fraction
• Length of longest subarray with at most k frequency
• Longest duplicate substring
• Longest harmonious subsequence
• Longest subarray of 1s after deleting one element
• Longest substring without repeating characters
• Max consecutive ones iii
• Maximize the confusion of an exam
• Maximize win from two segments
• Maximum beauty of an array after applying operation
• Maximum erasure value
• Maximum number of vowels in a substring of given length
• Maximum points you can obtain from cards
• Maximum strong pair xor i
• Maximum strong pair xor ii
• Maximum sum of almost unique subarray
• Maximum sum of distinct subarrays with length k
• Minimum moves to pick k ones
• Minimum number of operations to make array continuous
• Minimum operations to reduce x to zero
• Minimum recolors to get k consecutive black blocks
• Minimum rectangles to cover points
• Minimum size subarray sum
• Minimum window substring
• Permutation in string
• Sliding subarray beauty
• Subarrays with k different integers
• Subsequence with the minimum score

Monotonic deque

• Maximum number of robots within budget

String hashing

• Find beautiful indices in the given array i
• Find beautiful indices in the given array ii
• Implement strstr

Sorting

• Can make arithmetic progression from sequence
• Check if array is good
• Check if the number is fascinating
• Count the number of fair pairs
• Delete greatest value in each row
• Divide players into teams of equal skill
• Find all people with secret
• High access employees
• Largest perimeter triangle
• Largest submatrix with rearrangements
• Longest square streak in an array
• Majority element
• Maximize area of square hole in grid
• Maximum area of a piece of cake after horizontal and vertical cuts
• Maximum gap
• Maximum star sum of a graph
• Minimum absolute difference
• Minimum number of operations to make array continuous
• Minimum number of operations to make arrays similar
• Movement of robots
• Number of distinct averages
• Reduction operations to make the array elements equal
• Sum in a matrix
• The number of beautiful subsets
• The number of weak characters in the game
• Widest vertical area between two points containing no points

Custom

• Advantage shuffle
• Array of doubled pairs
• Best team with no conflicts
• Checking existence of edge length limited paths
• Closest room
• Concatenated words
• Container with most water
• Course schedule iii
• Custom sort string
• Design a food rating system
• Diagonal traverse ii
• Divide intervals into minimum number of groups
• Earliest possible day of full bloom
• Eliminate maximum number of monsters
• Find the number of ways to place people i
• Find the number of ways to place people ii
• K closest points to origin
• Largest number
• Longest string chain
• Maximize the profit as the salesman
• Maximum length of pair chain
• Maximum number of points from grid queries
• Maximum profit in job scheduling
• Maximum units on a truck
• Merge k sorted lists
• Minimum number of arrows to burst balloons
• Minimum number of taps to open to water a garden
• Minimum sum of squared difference
• Next greater element iv
• Non overlapping intervals
• Reward top k students
• Sort integers by the number of 1 bits
• Sort the people
• Sort the students by their kth score

Implementation

• Sort an array

Index array

• Apply operations to maximize score
• Best team with no conflicts
• Checking existence of edge length limited paths
• Count zero request servers
• Find score of an array after marking all elements
• Ipo
• Make array empty
• Maximum elegance of a k length subsequence
• Maximum subsequence score
• Maximum sum queries
• Minimum time to make array sum at most x
• Robot collisions

Merge sort

• Merge k sorted lists
• Merge sorted array
• Merge two sorted lists

Partial

• Buy two chocolates
• K closest points to origin
• Kth largest sum in a binary tree
• Make k subarray sums equal
• Mice and cheese
• Neither minimum nor maximum

Queries and updates together

• Count zero request servers
• Minimum space wasted from packaging
• Number of flowers in full bloom
• Number of good paths

Remembering index

• Closest nodes queries in a binary search tree
• Find right interval
• Invalid transactions
• Make lexicographically smallest array by swapping elements
• Mark elements on array by performing queries
• Relative ranks
• Sum of subarray minimums

Stable

• Difference between maximum and minimum price sum
• Query kth smallest trimmed number

Stack

• Binary search tree iterator
• Build an array with stack operations
• Min stack
• Removing stars from a string

Depth first search

• Binary tree inorder traversal
• Find eventual safe states

From array elements

• Asteroid collision
• Longest valid parentheses
• Make the string great
• Minimum string length after removing substrings
• Remove all adjacent duplicates in string ii
• Using a robot to print the lexicographically smallest string

Monotonic stack

• Apply operations to maximize score
• Beautiful towers ii
• Daily temperatures
• Find building where alice and bob can meet
• Find the number of subarrays where boundary elements are maximum
• Largest rectangle in histogram
• Maximum score of a good subarray
• Maximum subarray min product
• Maximum sum queries
• Minimum difficulty of a job schedule
• Next greater element ii
• Online stock span

Numerical operations

• Baseball game
• Basic calculator
• Basic calculator ii
• Evaluate reverse polish notation
• Minimum cost to change the final value of expression

String

Anagrams

• Group anagrams

Parsing

• Basic calculator
• Basic calculator ii
• Circular sentence
• Compare version numbers
• Complex number multiplication
• Count anagrams
• Count days spent together
• Detect capital
• Evaluate the bracket pairs of a string
• Find duplicate file in system
• Goat latin
• Invalid transactions
• Length of last word
• Minimum cost to change the final value of expression
• Number of different integers in a string
• Reverse words in a string iii
• Reward top k students
• Split message based on limit
• Split strings by separator
• Utf 8 validation

Recursive

• Decode string
• Number of atoms

Search

• Shortest uncommon substring in an array

Hashing

• Concatenated words
• Count prefix and suffix pairs i
• Count prefix and suffix pairs ii
• Find beautiful indices in the given array i
• Find beautiful indices in the given array ii
• Implement strstr
• Longest duplicate substring
• Maximum deletions on a string
• Minimum time to revert word to initial state i
• Minimum time to revert word to initial state ii
• Number of subarrays that match a pattern i
• Number of subarrays that match a pattern ii
• Palindrome pairs
• String transformation
• Sum of prefix scores of strings

Prefix/Suffix

• Prefix and suffix search
• Shortest string that contains three strings

Trie

• Length of the longest valid substring
• Longest common suffix queries

Subsequence

• Append characters to string to make subsequence
• Is subsequence
• Longest common subsequence
• Longest uncommon subsequence ii
• Longest word in dictionary through deleting
• Make string a subsequence using cyclic increments
• Maximum number of removable characters
• Number of matching subsequences
• Remove duplicate letters
• Subsequence with the minimum score

Suffix array

• Query kth smallest trimmed number

Validation

• Ambiguous coordinates
• Number of valid clock times

Time reversed simulation

• Backspace string compare
• Construct target array with multiple sums
• Maximum segment sum after removals
• Maximum spending after buying items
• Sum of matrix after queries

Tree

Binary search tree

• Insert into a binary search tree
• Kth smallest element in a bst
• Minimum absolute difference in bst
• Minimum distance between bst nodes
• Number of ways to reorder array to get same bst
• Range sum of bst
• Recover binary search tree

Traversal

• All elements in two binary search trees
• Binary search tree iterator
• Construct binary search tree from preorder traversal
• Convert bst to greater tree
• Delete node in a bst
• Increasing order search tree

Binary tree

• Cycle length queries in a tree

Iteration

• Binary tree inorder traversal
• Make costs of paths equal in a binary tree
• Maximum level sum of a binary tree
• Populating next right pointers in each node ii

Recursion

• Add one row to tree
• All nodes distance k in binary tree
• All possible full binary trees
• Average of levels in binary tree
• Balanced binary tree
• Binary tree cameras
• Binary tree level order traversal
• Binary tree level order traversal ii
• Binary tree maximum path sum
• Binary tree preorder traversal
• Binary tree pruning
• Binary tree right side view
• Binary tree tilt
• Binary tree zigzag level order traversal
• Check completeness of a binary tree
• Check if a string is a valid sequence from root to leaves path in a binary tree
• Construct binary search tree from preorder traversal
• Construct binary tree from inorder and postorder traversal
• Construct binary tree from preorder and inorder traversal
• Construct string from binary tree
• Convert bst to greater tree
• Convert sorted array to binary search tree
• Convert sorted list to binary search tree
• Count good nodes in binary tree
• Count nodes equal to average of subtree
• Cousins in binary tree
• Cousins in binary tree ii
• Deepest leaves sum
• Delete node in a bst
• Delete nodes and return forest
• Diameter of binary tree
• Distribute coins in binary tree
• Evaluate boolean binary tree
• Even odd tree
• Find a corresponding node of a binary tree in a clone of that tree
• Find bottom left tree value
• Find duplicate subtrees
• Find largest value in each tree row
• Find mode in binary search tree
• Flatten binary tree to linked list
• Flip binary tree to match preorder traversal
• Height of binary tree after subtree removal queries
• House robber iii
• Increasing order search tree
• Invert binary tree
• Kth largest sum in a binary tree
• Kth smallest element in a bst
• Leaf similar trees
• Longest univalue path
• Longest zigzag path in a binary tree
• Lowest common ancestor of a binary search tree
• Lowest common ancestor of a binary tree
• Maximum depth of binary tree
• Maximum difference between node and ancestor
• Maximum product of splitted binary tree
• Maximum width of binary tree
• Minimum absolute difference in bst
• Minimum depth of binary tree
• Minimum distance between bst nodes
• Minimum number of operations to sort a binary tree by level
• Number of ways to reorder array to get same bst
• Path sum
• Path sum ii
• Path sum iii
• Populating next right pointers in each node
• Pseudo palindromic paths in a binary tree
• Range sum of bst
• Recover binary search tree
• Smallest string starting from leaf
• Symmetric tree
• Validate binary tree nodes

Hashing

• Find duplicate subtrees

Level-wise processing

• Maximum level sum of a binary tree
• Minimum number of operations to sort a binary tree by level

Order traversal

• Binary tree preorder traversal
• Construct binary tree from inorder and postorder traversal
• Construct binary tree from preorder and inorder traversal
• Flip binary tree to match preorder traversal
• Height of binary tree after subtree removal queries
• N ary tree level order traversal
• N ary tree preorder traversal
• Reverse odd levels of binary tree

Rerooting

• Amount of time for binary tree to be infected

Trie

• Design add and search words data structure
• Implement trie prefix tree
• Length of the longest valid substring
• Longest common suffix queries
• Maximum strong pair xor i
• Maximum strong pair xor ii
• Word search ii

Two player games

• Predict the winner
• Stone game iii

Two pointers

• Assign cookies
• Find all people with secret
• Find indices with index and value difference i
• Find indices with index and value difference ii
• Find k closest elements
• Find the longest semi repetitive substring
• Make lexicographically smallest array by swapping elements
• Maximize greatness of an array
• Merge two 2d arrays by summing values
• Minimum common value
• Minimum length of string after deleting similar ends
• Number of subsequences that satisfy the given sum condition
• Rearrange array elements by sign
• Reverse vowels of a string

Unique elements in subarray

• Count unique characters of all substrings of a given string
• Longest nice subarray
• Longest substring without repeating characters
• Maximum erasure value
• Optimal partition of string

Unique/duplicate element finding with bizarro algorithms

• Find all duplicates in an array
• Find all numbers disappeared in an array
• Find missing and repeated values
• Find the difference
• First missing positive
• Missing number

Valid subarray counting

Iterate one endpoint and keep valid range for other

• Count subarrays with fixed bounds

Untagged

• Broken calculator
• Buddy strings
• Counting elements
• Decoded string at index
• Flip string to monotone increasing
• Leftmost column with at least a one
• Move pieces to obtain a string
• Range module
• Reordered power of 2
• Repeated dna sequences
• Repeated substring pattern
• Replace all digits with characters
• Replace elements in an array
• Reshape the matrix
• Reverse bits
• Reverse linked list
• Reverse linked list ii
• Reverse nodes in k group
• Reverse only letters
• Reverse pairs
• Reverse string
• Reverse words in a string
• Richest customer wealth
• Robot bounded in circle
• Roman to integer
• Rotate array
• Rotate image
• Rotate list
• Rotating the box
• Rotting oranges
• Running sum of 1d array
• Russian doll envelopes
• Same tree
• Score of parentheses
• Scramble string
• Search a 2d matrix
• Search a 2d matrix ii
• Search in a binary search tree
• Search in rotated sorted array
• Search in rotated sorted array ii
• Search insert position
• Search suggestions system
• Seat reservation manager
• Second largest digit in a string
• Selling pieces of wood
• Sentence similarity iii
• Sequential digits
• Serialize and deserialize binary tree
• Serialize and deserialize bst
• Set matrix zeroes
• Set mismatch
• Shift 2d grid
• Shifting letters
• Shifting letters ii
• Short encoding of words
• Shortest distance to a character
• Shortest impossible sequence of rolls
• Shortest palindrome
• Shortest path in a grid with obstacles elimination
• Shortest path in binary matrix
• Shortest path visiting all nodes
• Shortest subarray with sum at least k
• Shortest unsorted continuous subarray
• Shuffle an array
• Sign of the product of an array
• Simplify path
• Single element in a sorted array
• Single number
• Single number ii
• Single number iii
• Single threaded cpu
• Sliding puzzle
• Sliding window maximum
• Sliding window median
• Slowest key
• Smallest integer divisible by k
• Smallest number in infinite set
• Smallest range covering elements from k lists
• Smallest range ii
• Smallest string with a given numeric value
• Smallest string with swaps
• Smallest subtree with all the deepest nodes
• Snakes and ladders
• Sort array by increasing frequency
• Sort array by parity
• Sort array by parity ii
• Sort characters by frequency
• Sort colors
• Sort integers by the power value
• Sort items by groups respecting dependencies
• Sort list
• Sort the matrix diagonally
• Sorting the sentence
• Spiral matrix
• Spiral matrix ii
• Spiral matrix iv
• Split array into consecutive subsequences
• Split linked list in parts
• Splitting a string into descending consecutive values
• Sqrtx
• Squares of a sorted array
• Stamping the sequence
• Steps to make array non decreasing
• Stone game
• Stone game ii
• Stone game iv
• Stone game vii
• Stone game viii
• Stream of characters
• String compression
• String to integer atoi
• Strong password checker ii
• Subarray product less than k
• Subarray sum equals k
• Subarray with elements greater than varying threshold
• Subsets
• Subsets ii
• Substring with concatenation of all words
• Substrings of size three with distinct characters
• Subtree of another tree
• Successful pairs of spells and potions
• Sum of all subset xor totals
• Sum of beauty of all substrings
• Sum of digits in base k
• Sum of distances in tree
• Sum of floored pairs
• Sum of left leaves
• Sum of numbers with units digit k
• Sum of root to leaf binary numbers
• Sum of square numbers
• Sum root to leaf numbers
• Summary ranges
• Super palindromes
• Super washing machines
• Surrounded regions
• Swap nodes in pairs
• Swapping nodes in a linked list
• Swim in rising water
• Target sum
• Task scheduler
• Task scheduler ii
• Teemo attacking
• Tenth line
• Text justification
• The dining philosophers
• The earliest and latest rounds where players compete
• The k weakest rows in a matrix
• The kth factor of n
• The latest time to catch a bus
• The number of full rounds you have played
• The skyline problem
• Three equal parts
• Time based key value store
• Time needed to rearrange a binary string
• To lower case
• Top k frequent elements
• Top k frequent words
• Total appeal of a string
• Transform to chessboard
• Transpose matrix
• Trapping rain water
• Trapping rain water ii
• Triangle
• Trim a binary search tree
• Triples with bitwise and equal to zero
• Truncate sentence
• Two city scheduling
• Two sum
• Two sum ii input array is sorted
• Two sum iv input is a bst
• Ugly number ii
• Uncrossed lines
• Unique binary search trees
• Unique binary search trees ii
• Unique email addresses
• Unique morse code words
• Unique paths
• Unique paths ii
• Unique paths iii
• Valid anagram
• Valid mountain array
• Valid number
• Valid palindrome
• Valid palindrome ii
• Valid parentheses
• Valid parenthesis string
• Valid perfect square
• Valid square
• Valid sudoku
• Valid triangle number
• Validate binary search tree
• Validate ip address
• Validate stack sequences
• Verify preorder serialization of a binary tree
• Verifying an alien dictionary
• Vertical order traversal of a binary tree
• Vowel spellchecker
• Wiggle subsequence
• Wildcard matching
• Word break
• Word break ii
• Word ladder
• Word ladder ii
• Word pattern
• Word search
• Word subsets

Fraud

• Add strings
• Count complete tree nodes
• Find minimum in rotated sorted array
• Find minimum in rotated sorted array ii
• Find peak element
• Multiply strings
• Next permutation

Suboptimal solution

• Apply operations to make sum of array greater than or equal to k
• Check if all the integers in a range are covered
• Check if two string arrays are equivalent
• Counting bits
• Element appearing more than 25 in sorted array
• Extra characters in a string
• Find all numbers disappeared in an array
• Find the duplicate number
• Flatten nested list iterator
• How many numbers are smaller than the current number
• Kth missing positive number
• Longest increasing subsequence
• Longest strictly increasing or strictly decreasing subarray
• Longest substring with at least k repeating characters
• Longest word in dictionary
• Map sum pairs
• Maximum distance between a pair of values
• Maximum length substring with two occurrences
• Maximum score after splitting a string
• Next greater element i
• Split message based on limit