AlgoMaster DSA Animations

Bubble Sort

Sort an array using the bubble sort algorithm

Selection Sort

Sort an array using the selection sort algorithm

Insertion Sort

Sort an array using the insertion sort algorithm

Merge Sort (Iterative)

Sort an array using the bottom-up iterative merge sort algorithm

Bucket Sort

Sort elements by distributing them into buckets

Counting Sort

Sort elements by counting occurrences of each value

Heap Sort

Sort an array using a max-heap data structure

Maximum Gap

Find the maximum difference between successive elements after sorting

Radix Sort

Sort integers digit by digit from least to most significant

Shell Sort

Sort an array using diminishing increment sort

Sort an Array

Sort an array using an efficient comparison-based algorithm

Array

Move Zeroes

Move all zeroes to end while maintaining relative order

Majority Element

Find the majority element in an array

Remove Duplicates from Sorted Array

Remove duplicates from a sorted array

Best Time to Buy and Sell Stock

Find maximum profit from single buy and sell transaction

Rotate Array

Rotate an array by k steps

Product of Array Except Self

Calculate product of array except self

Best Time to Buy and Sell Stock II

Find maximum profit from multiple buy and sell transactions

Number of Zero-Filled Subarrays

Find number of zero-filled subarrays

Increasing Triplet Subsequence

Find increasing triplet subsequence

First Missing Positive

Find the first missing positive integer in an array

Apple Redistribution into Boxes

Find minimum boxes needed to redistribute apples

Contains Duplicate

Check if any value appears at least twice in the array

Contains Duplicate III

Find if there exist indices i, j with bounded index and value difference

Count Binary Substrings

Count substrings with equal numbers of 0s and 1s

Find All Numbers Disappeared in an Array

Find all numbers missing from 1 to n in an array

Majority Element II

Find all elements appearing more than n/3 times

Max Consecutive Ones

Find the maximum number of consecutive 1s in a binary array

Maximum Swap

Swap two digits at most once to get the maximum valued number

Missing Number

Find the missing number in range 0 to n

Missing Ranges

Find missing ranges between lower and upper bounds

Remove Element

Remove all occurrences of a value in-place

Set Mismatch

Find the number that occurs twice and the missing number

Shuffle the Array

Interleave two halves of an array in a specific pattern

Shortest Unsorted Continuous Subarray

Find the shortest subarray that when sorted makes the whole array sorted

Summary Ranges

Return the smallest sorted list of ranges covering all numbers in the array

Third Maximum Number

Find the third distinct maximum number in an array

Mo's Algorithm

Answer range queries efficiently using Mo's offline algorithm

String

Is Subsequence

Check if s is a subsequence of t

Valid Palindrome

Check if a string is a valid palindrome

Longest Common Prefix

Find the longest common prefix in an array of strings

Zigzag Conversion

Convert a string into a zigzag pattern across rows and read row by row

Reverse Words in a String

Reverse the words in a string

Repeated Substring Pattern

Check if a string can be constructed by repeating a substring

Repeated String Match

Find minimum repeats of a to contain b as substring

Number of Distinct Substrings in a String

Count distinct substrings using a Trie

Longest Happy Prefix

Find the longest prefix that is also a suffix using KMP

Shortest Palindrome

Find shortest palindrome by adding characters to the front

Longest Duplicate Substring

Find the longest substring that occurs at least twice using binary search and Rabin-Karp

Add Bold Tag in String

Add bold tags around substrings that match any word in a dictionary

Count and Say

Generate the nth term of the count-and-say sequence

Encode and Decode Strings

Design an algorithm to encode and decode a list of strings

Find the Length of the Longest Common Prefix

Find the longest common prefix length among pairs from two arrays

Integer to English Words

Convert a non-negative integer to its English words representation

KMP Algorithm

Search for a pattern in a text using the Knuth-Morris-Pratt algorithm

Length of Last Word

Return the length of the last word in a string

Longest Nice Substring

Find the longest substring where every letter appears in both cases

Number of Matching Subsequences

Count how many words are subsequences of a given string

One Edit Distance

Determine if two strings are exactly one edit apart

Palindrome Pairs

Find all pairs of distinct indices whose concatenation is a palindrome

Rabin-Karp String Search

Search for a pattern in text using rolling hash

Rotate String

Check if one string is a rotation of another

Special Binary String

Make the largest lexicographic special binary string by swapping

String Compression

Compress a character array using counts of repeated characters

Text Justification

Format text so that each line has exactly maxWidth characters

Valid Word Abbreviation

Determine if a word matches a given abbreviation

Words Within Two Edits of Dictionary

Find query words within two edit operations of any dictionary word

Z Algorithm

Build Z-array for pattern matching in linear time

Bit Manipulation

Single Number

Find the single number in an array where every other number appears twice

Counting Bits

Count the number of 1 bits in the binary representation of a number

Single Number III

Find the two numbers in an array where every other number appears twice

Hamming Distance

Find the number of positions where two integers differ in bits

Number of 1 Bits

Count the number of set bits in an integer

Reverse Bits

Reverse bits of a 32-bit unsigned integer

Single Number II

Find the element that appears once when others appear three times

Sum of Two Integers

Calculate the sum of two integers without using + or -

Hash Table

Ransom Note

Check if a ransom note can be constructed from a magazine

Number of Good Pairs

Find the number of good pairs in an array

Maximum Number of Balloons

Find the maximum number of balloons in a string

Contains Duplicate II

Check if an array contains duplicate elements within k distance

Isomorphic Strings

Check if two strings are isomorphic

Group Anagrams

Group anagrams together

Reorganize String

Reorganize a string so that no two adjacent characters are the same

Longest Consecutive Sequence

Find the longest consecutive sequence in an array

Number of Good Ways to Split a String

Find the number of good ways to split a string

Two Sum

Find two numbers in an array that add up to a target

Determine if Two Strings Are Close

Check if two strings are close by applying allowed operations

Encode and Decode TinyURL

Design a URL shortener service

First Unique Character in a String

Find the first non-repeating character in a string

Group Shifted Strings

Group strings that belong to the same shifting sequence

Happy Number

Determine if a number eventually reaches 1 under repeated digit-square summing

Insert Delete GetRandom O(1)

Design a data structure supporting O(1) insert, delete, and random access

Longest Palindrome

Find the length of the longest palindrome from given characters

Valid Anagram

Determine if two strings are anagrams of each other

Word Pattern

Determine if a string follows a given pattern

Two Pointers

Merge Sorted Array

Merge two sorted arrays into a single sorted array

Two Sum II - Input Array Is Sorted

Find two numbers that add up to target using two pointers on sorted array

Container with Most Water

Find two lines that form a container with maximum water capacity

3Sum

Find all unique triplets that sum to zero

Trapping Rain Water

Calculate total water trapped between elevation bars after raining

Backspace String Compare

Compare two strings after processing backspace characters

Remove Duplicates from Sorted Array II

Remove duplicates in-place allowing at most two of each element

Reverse String

Reverse a string in-place using two pointers

Squares of a Sorted Array

Return sorted array of squares of each number

Merge Strings Alternately

Merge two strings by alternating their characters

Valid Palindrome II

Check if a string can be a palindrome after deleting at most one character

Prefix Sum

Contiguous Array

Find longest subarray with equal number of 0s and 1s using hash map

Continuous Subarray Sum

Check if array has subarray (size ≥ 2) with sum that is multiple of k

Subarray Sum Equals K

Find subarrays with sum equal to target using prefix sums

Subarray Sum Divisible by K

Find subarrays with sum divisible by k using prefix sums

Running Sum of 1d Array

Compute running sum of each element in an array

Find Pivot Index

Find the index where the sum of left elements equals the sum of right elements

Maximum Population Year

Find the year with the highest population using a difference array

Range Addition

Apply range increment updates and return the final array

Sliding Window

Maximum Average Subarray I

Find maximum average of contiguous subarray of length k using sliding window

Permutation in String

Check if s1 is a permutation of s2 using sliding window

Find All Anagrams in a String

Find all anagrams of s1 in s2 using sliding window

Minimum Size Subarray Sum

Find minimal length subarray with sum ≥ target using variable-size sliding window

Max Consecutive Ones III

Find max consecutive 1s after flipping at most k zeros using sliding window

Longest Substring Without Repeating Characters

Find the length of the longest substring without repeating characters

Minimum Window Substring

Find the minimum window in string that contains all characters of target

Continuous Subarrays

Count subarrays where max-min difference is at most 2

Count Number of Nice Subarrays

Count subarrays with exactly k odd numbers

Count Subarrays With Fixed Bounds

Count subarrays where min is minK and max is maxK

Frequency of the Most Frequent Element

Find the maximum frequency of any element after k increments

Fruit Into Baskets

Pick the maximum number of fruits using two baskets

Longest Repeating Character Replacement

Find the longest substring with at most k character replacements

Longest Substring With At Least K Repeating Characters

Find the longest substring where every character repeats at least k times

Longest Substring With At Most K Distinct Characters

Find the longest substring containing at most k distinct characters

Longest Substring With At Most Two Distinct Characters

Find the longest substring with at most two distinct characters

Maximum Number of Vowels in a Substring of Given Length

Find the maximum number of vowels in any substring of length k

Maximum Points You Can Obtain from Cards

Pick k cards from the front or back of an array to maximize points

Maximum Sum of Distinct Subarrays With Length K

Find the maximum sum of a subarray of length k with all distinct elements

Minimum Window Subsequence

Find the minimum window in S that contains T as a subsequence

Partition Array Such That Maximum Difference Is K

Partition array into minimum subsequences with max-min difference at most k

Subarray Product Less Than K

Count subarrays where the product of all elements is less than k

Subarrays with K Different Integers

Count subarrays with exactly k distinct integers

Substring With Concatenation of All Words

Find all starting indices of substring(s) that are a concatenation of all words

Kadane's Algorithm

Maximum Subarray

Find the contiguous subarray with the largest sum (Kadane's Algorithm)

Maximum Product Subarray

Find the contiguous subarray with the largest product (Kadane's Algorithm)

Best Sightseeing Pair

Find the best sightseeing pair in an array

Maximum Absolute Sum of Any Subarray

Find the maximum absolute sum of any subarray

Maximum Subarray Sum with One Deletion

Find the maximum subarray sum after deleting at most one element

Maximum Sum Circular Subarray

Find the maximum subarray sum in a circular array

Matrix

Spiral Matrix

Traverse matrix in spiral order from outer to inner layers

Rotate Image

Rotate n×n matrix 90 degrees clockwise using transpose then reverse

Set Matrix Zeroes

Set entire row and column to zero if element is zero using O(1) space

Diagonal Traverse

Traverse a matrix diagonally

Transpose Matrix

Return the transpose of a given matrix

Valid Sudoku

Determine if a 9x9 Sudoku board is valid

Game of Life

Simulate Conway's Game of Life on a board

Increment Submatrices by One

Apply range increment operations on a matrix using prefix sums

Linked List

Middle of the Linked List

Find the middle node of a linked list

Remove Nth Node From End of List

Remove the nth node from the end of a linked list

Reverse Linked List

Reverse a singly linked list using three pointers

Reverse Linked List II

Reverse a sublist from position left to right in one pass

Reverse Nodes in k-Group

Reverse nodes in k-sized groups using iterative in-place reversal

Remove Duplicates from Sorted List II

Remove all nodes with duplicate values from a sorted linked list

Merge Two Sorted Lists

Merge two sorted linked lists into a single sorted linked list

Linked List Cycle II

Detect cycle and find entry point using Floyd's algorithm

Swap Nodes in Pairs

Swap every two adjacent nodes in a linked list

Partition List

Partition a linked list around a value x

Rotate List

Rotate a linked list to the right by k places

Add Two Numbers

Add two numbers represented by linked lists

Copy List with Random Pointer

Deep copy a linked list with random pointers using three-pass interleaving

Flatten a Multilevel Doubly Linked List

Flatten a multilevel doubly linked list by inserting child lists inline

Intersection of Two Linked Lists

Find the node where two linked lists intersect using two pointers

Add Two Numbers II

Add two numbers represented as linked lists where digits are stored forward

Convert Sorted List to Binary Search Tree

Convert a sorted linked list to a height-balanced binary search tree

Delete the Middle Node of a Linked List

Delete the middle node of a linked list

Delete Node in a Linked List

Delete a node in a linked list given only access to that node

Design Linked List

Implement a linked list with get, add, and delete operations

Insert Node in Linked List

Insert a node into a linked list

Insert into a Sorted Circular Linked List

Insert a value into a sorted circular linked list

LRU Cache

Design a data structure for a least recently used cache

Merge In Between Linked Lists

Replace nodes from index a to b in list1 with list2

Odd Even Linked List

Group odd-indexed nodes before even-indexed nodes in a linked list

Palindrome Linked List

Check whether a linked list is a palindrome

Remove Duplicates from Sorted List

Delete all duplicates from a sorted linked list

Reorder List

Reorder linked list to interleave nodes from front and back

Sort List

Sort a linked list in O(n log n) time using merge sort

Stack

Valid Parentheses

Determine if a string of brackets is properly balanced using a stack

Remove All Adjacent Duplicates In String

Remove all adjacent duplicates in a string using a stack

Remove Duplicate Letters

Remove duplicate letters from a string to form the lexicographically smallest string

Removing Stars From a String

Remove stars from a string

Evaluate Reverse Polish Notation

Evaluate a reverse polish notation expression using a stack

Basic Calculator II

Evaluate a basic calculator expression using a stack

Longest Valid Parentheses

Find the longest valid parentheses substring using a stack

Next Greater Element I

Find the next greater element for each element in nums1 using a stack

Daily Temperatures

Find how many days until a warmer temperature using monotonic stack

132 Pattern

Find the 132 pattern in an array using a stack

Number of Visible People in a Queue

Find the number of visible people in a queue using a stack

Largest Rectangle in Histogram

Find the largest rectangle area in a histogram using a monotonic stack

Asteroid Collision

Simulate collisions between asteroids moving in opposite directions

Baseball Game

Calculate a baseball game score based on a list of operations

Basic Calculator

Evaluate a basic arithmetic expression string with + and -

Buildings With an Ocean View

Find buildings that have an ocean view to the right

Car Fleet

Find the number of car fleets that arrive at a destination

Create Maximum Number

Create the maximum number from two arrays with length k

Decode String

Decode an encoded string with nested repetition patterns

Design a Text Editor

Design a text editor with add, delete, and cursor movement operations

Design Browser History

Implement browser history with visit, back, and forward operations

Exclusive Time of Functions

Calculate the exclusive time of each function from call logs

Find the Most Competitive Subsequence

Find the most competitive subsequence of length k

Implement Queue Using Stacks

Implement a FIFO queue using only two stacks

Implement Stack Using Queues

Implement a LIFO stack using only queues

Max Stack

Design a stack that supports push, pop, and retrieving the maximum element

Maximum Frequency Stack

Design a stack that pops the most frequent element

Maximum Nesting Depth of the Parentheses

Find the maximum nesting depth of parentheses in a string

Maximum Score From Removing Substrings

Maximize score by removing substrings ab and ba

Maximum Width Ramp

Find the maximum width ramp in an array

Min Stack

Design a stack that supports retrieving the minimum element in O(1)

Minimum Add to Make Parentheses Valid

Find the minimum number of parentheses to add to make a string valid

Minimum Remove to Make Valid Parentheses

Remove minimum parentheses to make the string valid

Next Greater Element II

Find the next greater element for each element in a circular array

Next Greater Node In Linked List

Find the next greater value for each node in a linked list

Online Stock Span

Calculate the price span for a stock on each day

Remove Invalid Parentheses

Remove the minimum number of invalid parentheses to make the string valid

Remove K Digits

Remove k digits from a number to make it as small as possible

Simplify Path

Simplify a Unix-style file path

Valid Parenthesis String

Check if a string with *, (, ) can be valid by replacing * appropriately

Validate Stack Sequences

Check if given pushed and popped sequences could result from a stack

Queue

Reveal Cards In Increasing Order

Arrange deck so cards are revealed in increasing order using queue simulation

Jump Game VI

Find the maximum score of a jump game using a queue

Sliding Window Maximum

Find maximum in each sliding window using monotonic deque

Max Value of Equation

Find the maximum value of equation using a queue

Design Circular Deque

Design a double-ended circular queue with fixed capacity

Design Circular Queue

Design a circular queue with enqueue, dequeue, and peek operations

Design Hit Counter

Design a hit counter that counts hits in the last 5 minutes

First Unique Number

Find the first unique number in a stream

Logger Rate Limiter

Design a logger that limits duplicate log messages to once per 10 seconds

Moving Average from Data Stream

Calculate the moving average of the last n numbers from a stream

Number of Recent Calls

Count requests in the last 3000 milliseconds

Time Needed to Buy Tickets

Find how long it takes for a person at position k to buy all their tickets

QuickSelect

Sort Colors

Sort an array of 0s, 1s, and 2s using the quickselect algorithm

Heaps

Kth Largest Element in an Array

Find the kth largest element in an array using a min-heap

Binary Search

Search Insert Position

Find the insertion position of a target in a sorted array using binary search

Search in Rotated Sorted Array

Find target in rotated sorted array using modified binary search

Find Peak Element

Find the peak element in a sorted array using binary search

Find Minimum in Rotated Sorted Array

Find the minimum element in a rotated sorted array using binary search

Search in 2D Matrix

Find target in sorted 2D matrix using binary search

Binary Search

Search for a target value in a sorted array

Capacity To Ship Packages Within D Days

Find the minimum ship capacity to deliver all packages within d days

Find First and Last Position of Element in Sorted Array

Find the starting and ending position of a target in a sorted array

Find First Occurrence

Find the first occurrence of a target in a sorted array

Find in Mountain Array

Find a target in a mountain array using binary search

Find K Closest Elements

Find the k closest integers to a target in a sorted array

Find K-th Smallest Pair Distance

Find the k-th smallest absolute difference among all pairs

Find Smallest Letter Greater Than Target

Find the smallest letter in a circular sorted list greater than the target

First Bad Version

Find the first bad version using binary search

Guess Number Higher or Lower

Guess a number between 1 and n using binary search

Koko Eating Bananas

Find the minimum eating speed to finish all bananas within h hours

Magnetic Force Between Two Balls

Maximize the minimum magnetic force between balls placed in baskets

Minimum Number of Days to Make m Bouquets

Find the minimum days to make m bouquets from the garden

Most Profit Assigning Work

Assign jobs to workers to maximize total profit

Search a 2D Matrix II

Search for a target in a matrix sorted row and column-wise

Search in Rotated Sorted Array II

Search for a target in a rotated sorted array that may contain duplicates

Snapshot Array

Design an array supporting snapshots and queries on past states

Split Array Largest Sum

Split array into m subarrays to minimize the largest subarray sum

Time Based Key-Value Store

Design a key-value store supporting time-stamped get and set operations

Valid Perfect Square

Determine if a number is a perfect square without using sqrt

Backtracking

Subsets

Generate all subsets using recursive backtracking with decision tree

Permutations

Generate all permutations by choosing unused elements recursively

Combination Sum

Find all combinations that sum to a target using reusable elements

Combination Sum II

Find all unique combinations that sum to a target with no reuse

Combination Sum III

Find all combinations of k numbers that sum to n

Combinations

Generate all combinations of k numbers from 1 to n

Generate Parentheses

Generate all combinations of well-formed parentheses

Letter Combinations of a Phone Number

Generate all possible letter combinations from a phone number

N-Queens

Place n queens on an n×n chessboard so no two queens attack each other

Palindrome Partitioning

Partition a string into all possible palindrome substrings

Permutations II

Generate all unique permutations of a collection that may have duplicates

Restore IP Addresses

Return all valid IP addresses that can be formed from a string

Subsets II

Generate all subsets of a collection that may have duplicates

Sudoku Solver

Solve a Sudoku puzzle by filling in the empty cells

Unique Paths III

Walk over every non-obstacle square exactly once from start to end

Word Search

Find if a word exists in a grid by searching adjacent cells

Word Squares

Build all word squares from a given set of words

Tree

Binary Tree Level Order Traversal

Traverse tree level by level using BFS and queue

Binary Tree Right Side View

Traverse tree right side view using BFS and queue

Binary Tree Zigzag Level Order Traversal

Traverse tree level by level in zigzag pattern using BFS and queue

Populating Next Right Pointers in Each Node II

Connect nodes at same level using BFS with queue

Binary Tree Preorder Traversal

Traverse tree preorder using DFS and stack

Same Tree

Check if two binary trees are identical

Symmetric Tree

Check if a binary tree is symmetric

Binary Tree Paths

Find all root-to-leaf paths in a binary tree

Convert Sorted Array to Binary Search Tree

Convert a sorted array to a binary search tree

Maximum Difference Between Node and Ancestor

Find the maximum difference between a node and its ancestor in a binary tree

Path Sum III

Count downward paths that sum to target using prefix sums and DFS

Binary Tree Inorder Traversal

Traverse tree inorder using DFS and stack

Minimum Distance Between BST Nodes

Find the minimum distance between any two nodes in a BST

Validate Binary Search Tree

Check if a binary tree satisfies BST properties using recursive DFS

Kth Smallest Element in a BST

Find the kth smallest element in a BST using iterative inorder traversal

Binary Tree Postorder Traversal

Traverse tree postorder using DFS and stack

Invert Binary Tree

Invert a binary tree using DFS and stack

Diameter of Binary Tree

Find the diameter of a binary tree using recursion

Lowest Common Ancestor of a Binary Tree

Find the lowest common ancestor of two nodes in a binary tree using recursion

Find Duplicate Subtrees

Find duplicate subtrees in a binary tree using serialization

Flatten Binary Tree to Linked List

Flatten tree to right-skewed linked list in-place using Morris Traversal

Distribute Coins in Binary Tree

Distribute coins to each node in a binary tree so that every node has exactly one coin

House Robber III

Find maximum amount of money the thief can rob from a binary tree

Binary Tree Maximum Path Sum

Find maximum path sum in tree where path can start and end at any node

Binary Tree Cameras

Find minimum number of cameras to cover all nodes in a binary tree

Average of Levels in Binary Tree

Return the average value of each level of a binary tree

Balanced Binary Tree

Determine if a binary tree is height-balanced

Boundary of Binary Tree

Return the boundary values of a binary tree in counter-clockwise order

Check Completeness of a Binary Tree

Determine if a binary tree is a complete binary tree

Construct Binary Tree from Inorder and Postorder Traversal

Build a binary tree from its inorder and postorder traversals

Construct Binary Tree from Preorder and Inorder Traversal

Build a binary tree from its preorder and inorder traversals

Construct Quad Tree

Construct a quad tree from a 2D grid

Count Complete Tree Nodes

Count nodes in a complete binary tree in less than O(n)

Count Good Nodes in Binary Tree

Count nodes where no node on the path from root has a greater value

Delete Nodes And Return Forest

Delete nodes from a binary tree and return the remaining forest

Longest Univalue Path

Find the longest path in a tree where all nodes have the same value

Maximum Binary Tree

Construct a maximum binary tree from an array

Maximum Width of Binary Tree

Find the maximum width of a binary tree across all levels

Path Sum II

Find all root-to-leaf paths that sum to a target

Populating Next Right Pointers in Each Node

Connect each node to its next right node at the same level

Serialize and Deserialize Binary Tree

Encode a binary tree to a string and decode it back

Step-By-Step Directions From a Binary Tree Node to Another

Find the shortest path between two nodes in a binary tree

Subtree of Another Tree

Check if a tree is a subtree of another tree

Sum of Left Leaves

Find the sum of all left leaves in a binary tree

Sum Root to Leaf Numbers

Calculate the total sum of all root-to-leaf numbers

Vertical Order Traversal of a Binary Tree

Traverse a binary tree column by column from left to right

BST

Trim Binary Search Tree

Trim BST to range [low, high] using recursive pruning and restructuring

Balance a Binary Search Tree

Convert an unbalanced BST into a balanced BST

Binary Search Tree Iterator

Implement an in-order iterator for a BST with O(h) memory

Closest Binary Search Tree Value

Find the value in a BST closest to a given target

Construct BST from Preorder Traversal

Construct a BST from its preorder traversal

Convert BST to Sorted Doubly Linked List

Convert a BST to a sorted circular doubly-linked list in-place

Delete from BST

Delete a node with a given key from a binary search tree

Delete Node in a BST

Delete a node in a BST and return the root

Inorder Successor in BST

Find the in-order successor of a node in a BST

Inorder Successor in BST II

Find the in-order successor when nodes have parent pointers

Insert into BST

Insert a value into a binary search tree

Insert into a Binary Search Tree

Insert a value into a BST and return the root

Largest BST Subtree

Find the largest subtree in a binary tree that is a valid BST

Lowest Common Ancestor of a BST

Find the lowest common ancestor of two nodes in a BST

Minimum Absolute Difference in BST

Find the minimum absolute difference between any two nodes in a BST

Range Sum of BST

Find the sum of all node values in a BST within a given range

Recover Binary Search Tree

Recover a BST where two nodes were swapped by mistake

Search in a Binary Search Tree

Find the node with the given value in a BST

Tries

Search Suggestions System

Generate product suggestions for each prefix using binary search

Word Search II

Find all words from dictionary in board using Trie and DFS backtracking

Design Add and Search Words Data Structure

Design a data structure that supports adding and searching with wildcards

Design In-Memory File System

Design an in-memory file system with ls, mkdir, addContentToFile, and readContentFromFile

Design Search Autocomplete System

Design a search autocomplete system that returns the top 3 historical hot sentences

Implement Trie

Implement a trie with insert, search, and startsWith operations

Implement Trie (Prefix Tree)

Implement a prefix tree supporting insert, search, and startsWith

Longest Word in Dictionary

Find the longest word that can be built one character at a time

Maximum XOR of Two Numbers in an Array

Find the maximum XOR of any two numbers in an array using a trie

Replace Words

Replace words in a sentence with their root from a dictionary

Stream of Characters

Detect words from a dictionary in a stream of characters

Heap

Sort Characters By Frequency

Sort characters by frequency using min-heap

Furthest Building You Can Reach

Find furthest building reachable with bricks and ladders using min-heap

Top K Frequent Elements

Find top k frequent elements using min-heap

Find Median from Data Stream

Find median from data stream using two heaps

IPO

Maximize capital by selecting k most profitable projects using max-heap

K Closest Points to Origin

Find k closest points to origin using max-heap to track distances

Find K Pairs with Smallest Sums

Find k pairs with smallest sums using min-heap

Merge k Sorted Lists

Merge k sorted lists using min-heap

All O'one Data Structure

Design a data structure with O(1) inc, dec, getMaxKey, and getMinKey

Employee Free Time

Find the free time intervals for all employees

Kth Largest Element in a Stream

Find the kth largest element in a stream of numbers

Find the Kth Largest Integer in the Array

Find the kth largest integer in a string array

Last Stone Weight

Simulate smashing the two heaviest stones until one remains

LFU Cache

Design a least-frequently-used cache with O(1) get and put

Maximum Performance of a Team

Pick at most k engineers to maximize the team's performance

Minimum Cost to Connect Sticks

Connect all sticks at minimum cost using a greedy approach with a min-heap

Minimum Cost to Hire K Workers

Hire exactly k workers with minimum total wage

Minimum Number of Refueling Stops

Find the minimum refueling stops to reach the target

Process Tasks Using Servers

Assign tasks to the smallest available server greedily

Single-Threaded CPU

Simulate a single-threaded CPU scheduling tasks by shortest processing time

The Skyline Problem

Find the skyline formed by a collection of buildings

Sliding Window Median

Find the median of each sliding window of size k

Smallest Range Covering Elements from K Lists

Find the smallest range that includes at least one number from each list

Stock Price Fluctuation

Track stock prices and query current, maximum, and minimum prices

Task Scheduler

Find the minimum time to execute all tasks with a cooldown constraint

Top K Frequent Words

Return the k most frequent words sorted by frequency and lexicographic order

Two Best Non-Overlapping Events

Pick at most two non-overlapping events to maximize the sum of values

Intervals

Merge Intervals

Merge all overlapping intervals on a timeline

Insert Interval

Insert a new interval into a list of intervals

Minimum Number of Arrows to Burst Balloons

Find minimum arrows needed to burst all balloons using greedy algorithm

Non-overlapping Intervals

Find maximum number of non-overlapping intervals using greedy algorithm

Kth Smallest Element in Sorted Matrix

Find kth smallest element using binary search on value range

Maximum Number of Events That Can Be Attended

Attend the maximum number of events using a greedy min-heap approach

Avoid Flood in The City

Prevent flooding by drying lakes before they overflow

Car Pooling

Determine if a car can pick up and drop off all passengers

Heaters

Find the minimum heater radius to cover all houses

Interval List Intersections

Find the intersection of two lists of closed intervals

Meeting Rooms

Determine if a person can attend all meetings

Meeting Rooms II

Find the minimum number of conference rooms required

Meeting Rooms III

Find the room that held the most meetings

Meeting Scheduler

Find the earliest available slot for a meeting of given duration

Minimum Interval to Include Each Query

For each query, find the size of the smallest interval that contains it

My Calendar I

Implement a calendar that books events without double-booking

My Calendar II

Implement a calendar allowing at most double-booking

Remove Covered Intervals

Remove intervals that are covered by another interval in the list

Set Intersection Size At Least Two

Find the minimum set whose intersection with every interval has size at least 2

Greedy

Jump Game II

Find minimum jumps to reach the end using greedy BFS approach

Gas Station

Find starting gas station to complete circular route using greedy algorithm

Assign Cookies

Assign cookies to children to maximize the number of content children

Boats to Save People

Find the minimum number of boats to carry all people

Candy

Distribute candy to children with minimum total using ratings

Jump Game

Determine if you can reach the last index from the first

Jump Game VII

Determine if you can reach the last index using jump constraints

Longest Happy String

Construct the longest string where no three consecutive characters are the same

Maximum Matrix Sum

Maximize the sum of a matrix by flipping signs of adjacent elements

Minimum Deletions to Make Character Frequencies Unique

Find the minimum deletions to make all character frequencies unique

Partition Labels

Partition a string into as many parts as possible so each letter appears in at most one part

Queue Reconstruction by Height

Reconstruct a queue based on people's heights and counts

Split Array into Consecutive Subsequences

Split an array into consecutive subsequences of at least length 3

Graph

Depth First Search

Traverse a graph using Depth First Search

Number of Islands

Count separate islands in a 2D grid using BFS flood-fill

Time Needed to Inform All Employees

Find the time needed to inform all employees using DFS with memoization

Employee Importance

Find the importance of an employee using DFS with memoization

Clone Graph

Clone a graph using DFS

Is Graph Bipartite?

Check if a graph is bipartite using DFS with coloring

All Nodes Distance K in Binary Tree

Find all nodes exactly K edges away from target using BFS with parent links

Rotting Oranges

Find minimum time for all oranges to rot using multi-source BFS

Word Ladder

Find shortest word transformation sequence using BFS

Course Schedule II

Find valid course order using DFS topological sort on prerequisite graph

Find Eventual Safe States

Find eventual safe states in a graph using DFS

Minimum Height Trees

Find minimum height trees in a graph using BFS

Number of Provinces

Count connected components in adjacency matrix using DFS

Redundant Connection

Find redundant connection in a graph using Union-Find

Minimize Malware Spread

Find redundant connection in a graph using Union-Find

Course Schedule IV

Check prerequisite relationships using BFS topological sort with ancestor sets

Parallel Courses

Find minimum semesters using BFS level-by-level topological sort

Flood Fill

Paint connected pixels with new color using recursive DFS

Number of Distinct Islands

Count distinct island shapes using DFS with path signatures

Find All Possible Recipes

Find makeable recipes using BFS from supplies through ingredient graph

Sort Items by Groups

Sort items respecting group and dependency constraints using dual topological sort

Alien Dictionary

Derive character ordering from sorted alien words using topological sort

Connected Components

Count connected components in undirected graph using Union-Find

Surrounded Regions

Capture surrounded O regions using DFS

Graph Valid Tree

Check if undirected graph forms a valid tree using Union-Find

Accounts Merge

Merge accounts with common emails using Union-Find

Evaluate Division

Evaluate variable division queries using weighted Union-Find

Most Stones Removed

Find max removable stones by grouping via row/col using Union-Find

Number of Islands II

Count islands after each addLand operation using online Union-Find

Critical Connections in a Network

Find bridges in graph using Tarjan's algorithm with disc/low arrays

Longest Path With Different Adjacent Characters

Find longest path in tree with different adjacent characters using post-order DFS

01 Matrix

Find distance to nearest zero using multi-source BFS

Walls and Gates

Fill rooms with distance to nearest gate using multi-source BFS

Open the Lock

Find minimum turns to open lock using BFS on combinations

Snakes and Ladders

Find minimum moves on board game using BFS

Minimum Genetic Mutation

Find minimum gene mutations using BFS on gene strings

Minimum Knight Moves

Find minimum knight moves to target using BFS

Shortest Path in Binary Matrix

Find shortest clear path using 8-directional BFS

Path With Maximum Minimum Value

Find path maximizing minimum value using binary search + BFS

Shortest Path with Obstacles Elimination

Find shortest path with obstacle elimination using BFS with 3D state

Bus Routes

Find minimum buses to reach destination using BFS on routes

Minimum Obstacle Removal to Reach Corner

Find minimum obstacles to remove using 0-1 BFS with deque

Cheapest Flights Within K Stops

Find cheapest price with at most K stops using Bellman-Ford variant

Path with Maximum Probability

Find path with maximum success probability using modified Dijkstra

Path With Minimum Effort

Find path minimizing maximum absolute height difference using Dijkstra

The Maze II

Find shortest distance in a maze with rolling ball using BFS

Minimum Cost to Convert String I

Find minimum cost to convert string using Floyd-Warshall on characters

Find Minimum Time to Reach Last Room I

Find minimum time to reach last room using modified Dijkstra on grid

Swim in Rising Water

Find minimum time to swim from top-left to bottom-right using Dijkstra

Minimum Cost to Make at Least One Valid Path in a Grid

Find minimum cost for valid path using 0-1 BFS with deque

Minimum Weighted Subgraph With the Required Paths

Find minimum weight subgraph connecting two sources to destination using triple Dijkstra

Min Cost to Connect All Points

Find minimum cost to connect all points using Kruskal's algorithm

Connecting Cities With Minimum Cost

Find minimum cost to connect all cities using Prim's algorithm

Optimize Water Distribution in a Village

Find minimum cost to supply water using Prim's algorithm with a virtual well node

Cracking the Safe

Find shortest string containing all codes using de Bruijn sequence

Valid Arrangement of Pairs

Find valid pair arrangement using Hierholzer's Eulerian path algorithm

A* Search Algorithm

Find the shortest path using heuristic-guided best-first search

All Paths From Source to Target

Find all paths from source to target in a DAG

Bellman-Ford Algorithm

Find shortest paths from a source, handling negative weights

Breadth First Search

Traverse a graph level by level using a queue

Centroid Decomposition

Decompose a tree by repeatedly finding and removing centroids

Find Critical and Pseudo-Critical Edges in MST

Identify critical and pseudo-critical edges in a minimum spanning tree

Detect Cycle in Directed Graph

Detect a cycle in a directed graph using DFS

Detect Cycle in Undirected Graph

Detect a cycle in an undirected graph using DFS or Union-Find

Dijkstra's Algorithm

Find shortest paths from a source in a weighted graph

Floyd-Warshall Algorithm

Find all-pairs shortest paths in a weighted graph

Heavy-Light Decomposition

Decompose a tree for efficient path queries

Kosaraju's SCC Algorithm

Find all strongly connected components in a directed graph

Kruskal's MST Algorithm

Find a minimum spanning tree using Kruskal's greedy approach

Making A Large Island

Find the largest island size after flipping at most one 0 to 1

Maximize Spanning Tree Stability

Find the spanning tree that maximizes the minimum edge weight

Network Delay Time

Find the time it takes for all nodes to receive a signal

Number of Connected Components in an Undirected Graph

Count connected components in an undirected graph

Number of Enclaves

Count land cells that cannot reach the boundary

Pacific Atlantic Water Flow

Find cells from which water can flow to both the Pacific and Atlantic ocean

Prim's MST Algorithm

Find a minimum spanning tree using Prim's greedy approach

Reconstruct Itinerary

Find a valid itinerary using all tickets in lexicographic order

Tarjan's Algorithm

Find strongly connected components using Tarjan's DFS-based algorithm

Topological Sort

Order nodes in a DAG such that all edges go from earlier to later nodes

Union-Find (Disjoint Set Union)

Track and merge disjoint sets with path compression and union by rank

Dynamic Programming

Longest Increasing Subsequence

Find the length of the longest increasing subsequence

Minimum Path Sum

Find the minimum path sum from top-left to bottom-right in a grid

Russian Doll Envelopes

Find max envelopes that can be Russian dolled using Sort + LIS

Climbing Stairs

Find the number of ways to climb to the top of the stairs

Min Cost Climbing Stairs

Find the minimum cost to climb to the top of the stairs

House Robber

Find maximum money to rob from houses using dynamic programming

House Robber II

Find maximum money to rob from houses in a circle using dynamic programming

Unique Paths II

Find number of unique paths to reach the bottom-right corner of a grid with obstacles using dynamic programming

Count Square Submatrices with All Ones

Find number of square submatrices with all ones using dynamic programming

Maximum Number of Points with Cost

Find maximum number of points with cost using dynamic programming

Burst Balloons

Find maximum number of points with cost using dynamic programming

Maximum Profit in Job Scheduling

Find maximum profit in job scheduling using dynamic programming

Longest Common Subsequence

Find length of longest subsequence common to both strings using dynamic programming

Edit Distance

Find minimum number of operations to convert one string to another using dynamic programming

Longest Palindromic Subsequence

Find length of longest palindromic subsequence using dynamic programming

Decode Ways

Find number of ways to decode a string using dynamic programming

Wildcard Matching

Check if one string matches the pattern using dynamic programming

Distinct Subsequences

Count number of ways to get t from s using dynamic programming

Coin Change

Find minimum number of coins to make amount using dynamic programming

Coin Change II

Count number of ways to make amount using coins with dynamic programming

Perfect Squares

Find minimum number of perfect squares that sum to n using dynamic programming

Partition Equal Subset Sum

Check if the array can be partitioned into two subsets with equal sum using dynamic programming

Target Sum

Find number of ways to target sum using dynamic programming

Last Stone Weight II

Find the minimum weight of the last stone using dynamic programming

Triangle

Find minimum path sum in a triangle using dynamic programming

Fibonacci Number

Compute the nth Fibonacci number using space-optimized DP

Maximum Length of Pair Chain

Find the longest chain of pairs using greedy sorting by end value

Delete and Earn

Maximize points by deleting numbers using house-robber style DP

Integer Break

Maximize the product of parts that sum to n using math and DP

Greatest Sum Divisible by Three

Find maximum sum divisible by 3 using remainder DP

Number of Ways to Paint N × 3 Grid

Count grid painting ways using pattern transition DP

Ones and Zeroes

Find max subset size with limited 0s and 1s using 2D knapsack DP

Profitable Schemes

Count schemes meeting profit threshold using 2D knapsack DP

Minimum Cost For Tickets

Find minimum cost for travel days using DP with ticket passes

Number of Longest Increasing Subsequence

Count the number of longest increasing subsequences using DP

Longest String Chain

Find the longest chain of words where each differs by one character

Longest Arithmetic Subsequence

Find the longest arithmetic subsequence using hash map DP

Pascal's Triangle

Generate Pascal's triangle row by row using dynamic programming

Unique Paths

Count unique paths in a grid using space-optimized DP

Maximal Square

Find the largest square of 1s in a binary matrix using DP

Paint House

Find minimum cost to paint houses with no two adjacent same color

Minimum Falling Path Sum

Find minimum sum falling path through a matrix using DP

Remove Boxes

Maximize points by removing boxes using 3D memoization DP

Maximal Rectangle

Find the largest rectangle of 1s in a binary matrix using width DP

Cherry Pickup

Collect maximum cherries with two walkers using simultaneous DP

Dungeon Game

Find minimum initial health to reach bottom-right using reverse DP

Longest Increasing Path in a Matrix

Find longest increasing path using BFS topological sort

Painting a Grid With Three Different Colors

Count grid colorings using state transition matrix exponentiation

Minimum Cost Path with Teleportations

Find minimum cost path with teleportation phases using multi-pass DP

Frog Jump

Determine if frog can cross river by jumping on stones using hash map DP

Optimal Account Balancing

Find minimum transfers to settle debts using bitmask subset DP

Minimum Difficulty of a Job Schedule

Partition jobs into d days minimizing total difficulty using monotonic stack DP

Minimum Cost to Cut a Stick

Find minimum cost to cut a stick at given positions using interval DP

Word Break

Determine if a string can be segmented into dictionary words using DP

Interleaving String

Check if s3 is formed by interleaving s1 and s2 using space-optimized DP

Minimum Deletions to Make String Balanced

Find minimum deletions to make string of a's and b's balanced using greedy DP

Word Break II

Find all possible sentences from dictionary words using recursive DFS with memoization

Regular Expression Matching

Match string against pattern with '.' and '*' using 2D bottom-up DP

Palindrome Partitioning II

Find minimum cuts for palindrome partitioning using expand-around-center DP

Strange Printer

Find minimum turns to print a string using interval DP with character merging

Shortest Common Supersequence

Build shortest supersequence of two strings using LCS DP with traceback

Unique Binary Search Trees II

Generate all structurally unique BSTs using bottom-up interval DP

Number of Ways to Arrive at Destination

Find the number of shortest paths using Dijkstra with counting

Sum of Distances in Tree

Compute distance sums for all nodes using rerooting DP with two DFS passes

Campus Bikes II

Assign workers to bikes minimizing total distance using bitmask DP

Partition to K Equal Sum Subsets

Partition array into k subsets of equal sum using bitmask DP with bucket fill

Minimum Number of Work Sessions

Find minimum work sessions using subset DP with session time constraint

Fair Distribution of Cookies

Distribute cookies among children minimizing unfairness using bitmask DP

Shortest Path Visiting All Nodes

Find shortest path visiting all nodes using BFS with bitmask DP

Count Numbers with Unique Digits

Count numbers with unique digits up to 10^n using combinatorial DP

Number of Digit One

Count occurrences of digit 1 in all numbers from 1 to n using digit analysis

Numbers At Most N Given Digit Set

Count numbers at most N formed from a given digit set using right-to-left DP

Knight Probability in Chessboard

Find probability of knight staying on board after k moves using grid DP

Soup Servings

Find probability of soup A being emptied first using 2D DP

New 21 Game

Find probability of score ≤ n using sliding window DP

Best Time to Buy and Sell Stock with Cooldown

Find max profit with cooldown using 3-state DP (held, sold, rest)

Best Time to Buy and Sell Stock with Transaction Fee

Find max profit with transaction fee using 2-state DP (cash, hold)

Best Time to Buy and Sell Stock III

Find max profit with at most 2 transactions using 4-state DP

Best Time to Buy and Sell Stock IV

Find max profit with at most k transactions using 2D DP with maxDiff optimization

Longest Palindromic Substring

Find the longest palindromic substring using dynamic programming

Concatenated Words

Find all words that can be formed by concatenating other words in the list

Constrained Subsequence Sum

Find the maximum sum subsequence where no two elements are more than k apart

Count of Range Sum

Count range sums that lie in a given interval

Number of People Aware of a Secret

Simulate how a secret spreads among people with delay and forget intervals

BIT / Segment Tree

Range Sum Query - Mutable

Handle point updates and range sum queries using a Binary Indexed Tree

Range Sum Query 2D - Mutable

Handle point updates and region sum queries using a 2D Binary Indexed Tree

Count of Smaller Numbers After Self

Count smaller elements to the right using a Binary Indexed Tree

Falling Squares

Simulate falling squares and track max height using a Segment Tree with lazy propagation

Block Placement Queries

Check if blocks fit between obstacles using a Segment Tree and sorted set

Longest Balanced Subarray II

Find the longest balanced subarray using a Lazy Segment Tree

Number of Pairs Satisfying Inequality

Count valid pairs using a Binary Indexed Tree on difference array

Fenwick Tree (Binary Indexed Tree)

Efficient data structure for prefix sum queries and point updates

Range Module

Track ranges of numbers and query if a range is covered

Range Sum Query 2D - Immutable

Answer sum queries on a 2D matrix using 2D prefix sums

Range Sum Query - Immutable

Answer range sum queries on an immutable array using prefix sums

Reverse Pairs

Count important reverse pairs using merge sort or BIT

Segment Tree

Build a segment tree for range sum queries and point updates

Segment Tree with Lazy Propagation

Handle range updates efficiently using lazy propagation in segment trees

Sparse Table

Preprocess an array for O(1) range minimum/maximum queries

Sqrt Decomposition

Answer range queries using square root decomposition

Math & Geometry

Palindrome Number

Check if a number reads the same forwards and backwards by reversing half

Reverse Integer

Reverse digits of a 32-bit signed integer with overflow detection

Factorial Trailing Zeroes

Count trailing zeroes in n! by counting factors of 5

Valid Square

Determine if four points form a valid square using pairwise distances

Minimum Area Rectangle II

Find the minimum area rectangle from a set of points in the xy-plane

Max Points on a Line

Find the maximum number of points that lie on the same straight line

Perfect Rectangle

Determine if rectangles form an exact cover of a rectangular region

Pow(x, n)

Implement fast exponentiation using repeated squaring

Rectangle Area II

Find the total area covered by a list of rectangles

Math / Geometry

Multiply Strings

Multiply two numbers represented as strings using digit-by-digit multiplication

Find the Duplicate Number

Find the duplicate in an array using Floyd's cycle detection

Count Good Numbers

Count good digit strings using binary exponentiation

Count Primes

Count primes less than n using the Sieve of Eratosthenes

Valid Triangle Number

Count valid triangles using sorting and two pointers

Minimum Area Rectangle

Find the minimum area rectangle from a set of points

Math

Plus One

Increment a number represented as an array of digits

Roman to Integer

Convert a Roman numeral string to an integer

Excel Sheet Column Title

Convert a column number to its Excel column title

Greatest Common Divisor of Strings

Find the largest string that divides both input strings

Ugly Number

Check if a number's prime factors are limited to 2, 3, and 5

Ugly Number II

Find the nth ugly number using three pointers