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AlgoMaster DSA Animations

Interactive visualizations for data structures and algorithms

Pattern Printing

Easy

Right-Angled Triangle of Stars

Print a triangle where row i has i stars

Easy

Inverted Right-Angled Triangle

Print a triangle that shrinks by one star each row

Easy

Pyramid of Stars

Print a centered pyramid using leading spaces and stars

Easy

Inverted Pyramid

Print a centered pyramid that narrows to a single star

Easy

Hollow Square

Print the border of a square while keeping the inside empty

Easy

Hollow Triangle

Print the edges of a triangle while keeping the inside empty

Easy

Diamond Pattern

Print a diamond by growing and then shrinking star rows

Easy

Floyd's Triangle

Fill a triangle with consecutive numbers row by row

Medium

Mirror Number Pattern

Print palindromic number rows that count up and back down

Medium

Butterfly Pattern

Print butterfly wings that grow to the middle and mirror back

Medium

Hourglass Pattern

Print an hourglass that narrows to a point and widens again

Medium

Spiral Number Pattern

Fill an n x n grid with numbers in clockwise spiral order

Sorting

Easy

Bubble Sort

Sort an array using the bubble sort algorithm

Easy

Selection Sort

Sort an array using the selection sort algorithm

Easy

Insertion Sort

Sort an array using the insertion sort algorithm

Medium

Shell Sort

Sort an array using gapped insertion sort with a shrinking gap

Medium

Merge Sort

Sort an array using merge sort, recursive top-down or iterative bottom-up

Medium

Quick Sort

Sort an array using the quick sort algorithm

Medium

Bucket Sort

Sort elements by distributing them into buckets

Easy

Counting Sort

Sort elements by counting occurrences of each value

Medium

Heap Sort

Sort an array using a max-heap data structure

Hard

Maximum Gap

Find the maximum difference between successive elements after sorting

Medium

Radix Sort

Sort integers digit by digit from least to most significant

Medium

Sort an Array

Sort an array using an efficient comparison-based algorithm

Array

Easy

Move Zeroes

Move all zeroes to end while maintaining relative order

Easy

Majority Element

Find the majority element in an array

Easy

Remove Duplicates from Sorted Array

Remove duplicates from a sorted array

Easy

Best Time to Buy and Sell Stock

Find maximum profit from single buy and sell transaction

Medium

Rotate Array

Rotate an array by k steps

Medium

Product of Array Except Self

Calculate product of array except self

Medium

Best Time to Buy and Sell Stock II

Find maximum profit from multiple buy and sell transactions

Medium

Number of Zero-Filled Subarrays

Find number of zero-filled subarrays

Medium

Increasing Triplet Subsequence

Find increasing triplet subsequence

Hard

First Missing Positive

Find the first missing positive integer in an array

Easy

Apple Redistribution into Boxes

Find minimum boxes needed to redistribute apples

Easy

Contains Duplicate

Check if any value appears at least twice in the array

Hard

Contains Duplicate III

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

Easy

Count Binary Substrings

Count substrings with equal numbers of 0s and 1s

Easy

Find All Numbers Disappeared in an Array

Find all numbers missing from 1 to n in an array

Medium

Majority Element II

Find all elements appearing more than n/3 times

Easy

Max Consecutive Ones

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

Medium

Maximum Swap

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

Easy

Missing Number

Find the missing number in range 0 to n

Easy

Missing Ranges

Find missing ranges between lower and upper bounds

Easy

Remove Element

Remove all occurrences of a value in-place

Easy

Set Mismatch

Find the number that occurs twice and the missing number

Easy

Shuffle the Array

Interleave two halves of an array in a specific pattern

Medium

Shortest Unsorted Continuous Subarray

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

Easy

Summary Ranges

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

Easy

Third Maximum Number

Find the third distinct maximum number in an array

Medium

Mo's Algorithm

Answer range queries efficiently using Mo's offline algorithm

String

Easy

Is Subsequence

Check if s is a subsequence of t

Easy

Valid Palindrome

Check if a string is a valid palindrome

Easy

Longest Common Prefix

Find the longest common prefix in an array of strings

Medium

Zigzag Conversion

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

Medium

Reverse Words in a String

Reverse the words in a string

Easy

Repeated Substring Pattern

Check if a string can be constructed by repeating a substring

Medium

Repeated String Match

Find minimum repeats of a to contain b as substring

Medium

Number of Distinct Substrings in a String

Count distinct substrings using a Trie

Hard

Longest Happy Prefix

Find the longest prefix that is also a suffix using KMP

Hard

Shortest Palindrome

Find shortest palindrome by adding characters to the front

Hard

Longest Duplicate Substring

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

Medium

Add Bold Tag in String

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

Medium

Count and Say

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

Medium

Encode and Decode Strings

Design an algorithm to encode and decode a list of strings

Medium

Find the Length of the Longest Common Prefix

Find the longest common prefix length among pairs from two arrays

Hard

Guess the Word

Find a secret word by guessing and filtering candidates by match count

Hard

Integer to English Words

Convert a non-negative integer to its English words representation

Medium

KMP Algorithm

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

Easy

Length of Last Word

Return the length of the last word in a string

Easy

Longest Nice Substring

Find the longest substring where every letter appears in both cases

Medium

Number of Matching Subsequences

Count how many words are subsequences of a given string

Medium

One Edit Distance

Determine if two strings are exactly one edit apart

Hard

Palindrome Pairs

Find all pairs of distinct indices whose concatenation is a palindrome

Medium

Rabin-Karp String Search

Search for a pattern in text using rolling hash

Easy

Rotate String

Check if one string is a rotation of another

Hard

Special Binary String

Make the largest lexicographic special binary string by swapping

Medium

String Compression

Compress a character array using counts of repeated characters

Hard

Text Justification

Format text so that each line has exactly maxWidth characters

Easy

Valid Word Abbreviation

Determine if a word matches a given abbreviation

Medium

Words Within Two Edits of Dictionary

Find query words within two edit operations of any dictionary word

Medium

Z Algorithm

Build Z-array for pattern matching in linear time

Bit Manipulation

Easy

Single Number

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

Easy

Counting Bits

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

Medium

Single Number III

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

Easy

Hamming Distance

Find the number of positions where two integers differ in bits

Easy

Number of 1 Bits

Count the number of set bits in an integer

Easy

Reverse Bits

Reverse bits of a 32-bit unsigned integer

Medium

Single Number II

Find the element that appears once when others appear three times

Medium

Sum of Two Integers

Calculate the sum of two integers without using + or -

Medium

Bitwise AND of Numbers Range

Find the bitwise AND of all numbers in a range via their common prefix

Hash Table

Easy

Ransom Note

Check if a ransom note can be constructed from a magazine

Easy

Number of Good Pairs

Find the number of good pairs in an array

Easy

Maximum Number of Balloons

Find the maximum number of balloons in a string

Easy

Contains Duplicate II

Check if an array contains duplicate elements within k distance

Easy

Isomorphic Strings

Check if two strings are isomorphic

Medium

Group Anagrams

Group anagrams together

Medium

Reorganize String

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

Medium

Longest Consecutive Sequence

Find the longest consecutive sequence in an array

Medium

Number of Good Ways to Split a String

Find the number of good ways to split a string

Easy

Two Sum

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

Medium

Determine if Two Strings Are Close

Check if two strings are close by applying allowed operations

Medium

Encode and Decode TinyURL

Design a URL shortener service

Easy

First Unique Character in a String

Find the first non-repeating character in a string

Medium

Group Shifted Strings

Group strings that belong to the same shifting sequence

Easy

Happy Number

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

Medium

Insert Delete GetRandom O(1)

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

Easy

Longest Palindrome

Find the length of the longest palindrome from given characters

Easy

Valid Anagram

Determine if two strings are anagrams of each other

Easy

Word Pattern

Determine if a string follows a given pattern

Easy

Design HashMap

Design a HashMap from scratch without built-in hash table libraries

Easy

Intersection of Two Arrays II

Find the intersection of two arrays including duplicates using a hash map

Two Pointers

Easy

Merge Sorted Array

Merge two sorted arrays into a single sorted array

Medium

Two Sum II - Input Array Is Sorted

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

Medium

Container with Most Water

Find two lines that form a container with maximum water capacity

Medium

3Sum

Find all unique triplets that sum to zero

Hard

Trapping Rain Water

Calculate total water trapped between elevation bars after raining

Easy

Backspace String Compare

Compare two strings after processing backspace characters

Medium

Remove Duplicates from Sorted Array II

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

Easy

Reverse String

Reverse a string in-place using two pointers

Easy

Squares of a Sorted Array

Return sorted array of squares of each number

Easy

Merge Strings Alternately

Merge two strings by alternating their characters

Easy

Valid Palindrome II

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

Medium

Next Permutation

Rearrange numbers into the next lexicographically greater permutation

Prefix Sum

Medium

Contiguous Array

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

Medium

Continuous Subarray Sum

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

Medium

Subarray Sum Equals K

Find subarrays with sum equal to target using prefix sums

Medium

Subarray Sum Divisible by K

Find subarrays with sum divisible by k using prefix sums

Easy

Running Sum of 1d Array

Compute running sum of each element in an array

Easy

Find Pivot Index

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

Easy

Maximum Population Year

Find the year with the highest population using a difference array

Medium

Range Addition

Apply range increment updates and return the final array

Medium

Matrix Block Sum

Compute the block sum around each cell using a 2D prefix sum

Sliding Window

Easy

Maximum Average Subarray I

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

Medium

Permutation in String

Check if s1 is a permutation of s2 using sliding window

Medium

Find All Anagrams in a String

Find all anagrams of s1 in s2 using sliding window

Medium

Minimum Size Subarray Sum

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

Medium

Max Consecutive Ones III

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

Medium

Longest Substring Without Repeating Characters

Find the length of the longest substring without repeating characters

Hard

Minimum Window Substring

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

Medium

Continuous Subarrays

Count subarrays where max-min difference is at most 2

Medium

Count Number of Nice Subarrays

Count subarrays with exactly k odd numbers

Hard

Count Subarrays With Fixed Bounds

Count subarrays where min is minK and max is maxK

Medium

Frequency of the Most Frequent Element

Find the maximum frequency of any element after k increments

Medium

Fruit Into Baskets

Pick the maximum number of fruits using two baskets

Medium

Longest Repeating Character Replacement

Find the longest substring with at most k character replacements

Medium

Longest Substring With At Least K Repeating Characters

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

Medium

Longest Substring With At Most K Distinct Characters

Find the longest substring containing at most k distinct characters

Medium

Longest Substring With At Most Two Distinct Characters

Find the longest substring with at most two distinct characters

Medium

Maximum Number of Vowels in a Substring of Given Length

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

Medium

Maximum Points You Can Obtain from Cards

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

Medium

Maximum Sum of Distinct Subarrays With Length K

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

Hard

Minimum Window Subsequence

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

Medium

Partition Array Such That Maximum Difference Is K

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

Medium

Subarray Product Less Than K

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

Hard

Subarrays with K Different Integers

Count subarrays with exactly k distinct integers

Hard

Substring With Concatenation of All Words

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

Medium

Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit

Find the longest subarray where max minus min stays within a limit using deques

Medium

Longest Turbulent Subarray

Find the longest subarray with alternating comparisons between adjacent elements

Hard

Shortest Subarray with Sum at Least K

Find the shortest subarray with sum at least K using a monotonic deque

Kadane's Algorithm

Medium

Maximum Subarray

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

Medium

Maximum Product Subarray

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

Medium

Best Sightseeing Pair

Find the best sightseeing pair in an array

Medium

Maximum Absolute Sum of Any Subarray

Find the maximum absolute sum of any subarray

Medium

Maximum Subarray Sum with One Deletion

Find the maximum subarray sum after deleting at most one element

Medium

Maximum Sum Circular Subarray

Find the maximum subarray sum in a circular array

Matrix

Medium

Spiral Matrix

Traverse matrix in spiral order from outer to inner layers

Medium

Rotate Image

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

Medium

Set Matrix Zeroes

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

Medium

Diagonal Traverse

Traverse a matrix diagonally

Easy

Transpose Matrix

Return the transpose of a given matrix

Medium

Valid Sudoku

Determine if a 9x9 Sudoku board is valid

Medium

Game of Life

Simulate Conway's Game of Life on a board

Medium

Candy Crush

Crush groups of 3+ candies and apply gravity until the board is stable

Medium

Increment Submatrices by One

Apply range increment operations on a matrix using prefix sums

Medium

Spiral Matrix II

Fill an n by n matrix with values in spiral order

Linked List

Easy

Middle of the Linked List

Find the middle node of a linked list

Medium

Remove Nth Node From End of List

Remove the nth node from the end of a linked list

Easy

Reverse Linked List

Reverse a singly linked list using three pointers

Medium

Reverse Linked List II

Reverse a sublist from position left to right in one pass

Hard

Reverse Nodes in k-Group

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

Medium

Remove Duplicates from Sorted List II

Remove all nodes with duplicate values from a sorted linked list

Medium

Merge Two Sorted Lists

Merge two sorted linked lists into a single sorted linked list

Medium

Linked List Cycle II

Detect cycle and find entry point using Floyd's algorithm

Medium

Swap Nodes in Pairs

Swap every two adjacent nodes in a linked list

Medium

Partition List

Partition a linked list around a value x

Medium

Rotate List

Rotate a linked list to the right by k places

Medium

Add Two Numbers

Add two numbers represented by linked lists

Medium

Copy List with Random Pointer

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

Medium

Flatten a Multilevel Doubly Linked List

Flatten a multilevel doubly linked list by inserting child lists inline

Easy

Intersection of Two Linked Lists

Find the node where two linked lists intersect using two pointers

Medium

Add Two Numbers II

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

Medium

Convert Sorted List to Binary Search Tree

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

Medium

Delete the Middle Node of a Linked List

Delete the middle node of a linked list

Medium

Delete Node in a Linked List

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

Medium

Design Linked List

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

Easy

Insert Node in Linked List

Insert a node into a linked list

Medium

Insert into a Sorted Circular Linked List

Insert a value into a sorted circular linked list

Medium

LRU Cache

Design a data structure for a least recently used cache

Medium

Merge In Between Linked Lists

Replace nodes from index a to b in list1 with list2

Medium

Odd Even Linked List

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

Easy

Palindrome Linked List

Check whether a linked list is a palindrome

Easy

Remove Duplicates from Sorted List

Delete all duplicates from a sorted linked list

Medium

Reorder List

Reorder linked list to interleave nodes from front and back

Medium

Sort List

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

Stack

Easy

Valid Parentheses

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

Easy

Remove All Adjacent Duplicates In String

Remove all adjacent duplicates in a string using a stack

Medium

Remove Duplicate Letters

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

Medium

Removing Stars From a String

Remove stars from a string

Medium

Evaluate Reverse Polish Notation

Evaluate a reverse polish notation expression using a stack

Medium

Basic Calculator II

Evaluate a basic calculator expression using a stack

Hard

Longest Valid Parentheses

Find the longest valid parentheses substring using a stack

Easy

Next Greater Element I

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

Medium

Daily Temperatures

Find how many days until a warmer temperature using monotonic stack

Medium

132 Pattern

Find the 132 pattern in an array using a stack

Hard

Number of Visible People in a Queue

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

Hard

Largest Rectangle in Histogram

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

Medium

Asteroid Collision

Simulate collisions between asteroids moving in opposite directions

Easy

Baseball Game

Calculate a baseball game score based on a list of operations

Hard

Basic Calculator

Evaluate a basic arithmetic expression string with + and -

Medium

Buildings With an Ocean View

Find buildings that have an ocean view to the right

Medium

Car Fleet

Find the number of car fleets that arrive at a destination

Hard

Create Maximum Number

Create the maximum number from two arrays with length k

Medium

Decode String

Decode an encoded string with nested repetition patterns

Hard

Design a Text Editor

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

Medium

Design Browser History

Implement browser history with visit, back, and forward operations

Medium

Exclusive Time of Functions

Calculate the exclusive time of each function from call logs

Medium

Find the Most Competitive Subsequence

Find the most competitive subsequence of length k

Easy

Implement Queue Using Stacks

Implement a FIFO queue using only two stacks

Easy

Implement Stack Using Queues

Implement a LIFO stack using only queues

Hard

Max Stack

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

Hard

Maximum Frequency Stack

Design a stack that pops the most frequent element

Easy

Maximum Nesting Depth of the Parentheses

Find the maximum nesting depth of parentheses in a string

Medium

Maximum Score From Removing Substrings

Maximize score by removing substrings ab and ba

Medium

Maximum Width Ramp

Find the maximum width ramp in an array

Medium

Min Stack

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

Medium

Minimum Add to Make Parentheses Valid

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

Medium

Minimum Remove to Make Valid Parentheses

Remove minimum parentheses to make the string valid

Medium

Next Greater Element II

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

Medium

Next Greater Node In Linked List

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

Medium

Online Stock Span

Calculate the price span for a stock on each day

Hard

Remove Invalid Parentheses

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

Medium

Remove K Digits

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

Medium

Simplify Path

Simplify a Unix-style file path

Medium

Valid Parenthesis String

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

Medium

Validate Stack Sequences

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

Easy

Final Prices With a Special Discount in a Shop

Apply the next-smaller-price discount to each item using a monotonic stack

Medium

Max Chunks To Make Sorted

Find the maximum number of chunks an array can split into and still sort

Medium

Sum of Subarray Minimums

Sum the minimum of every subarray using a monotonic stack

Medium

Sum of Subarray Ranges

Sum max minus min over all subarrays using monotonic stacks

Queue

Medium

Reveal Cards In Increasing Order

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

Medium

Jump Game VI

Find the maximum score of a jump game using a queue

Hard

Sliding Window Maximum

Find maximum in each sliding window using monotonic deque

Hard

Max Value of Equation

Find the maximum value of equation using a queue

Medium

Design Circular Deque

Design a double-ended circular queue with fixed capacity

Medium

Design Circular Queue

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

Medium

Design Hit Counter

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

Medium

First Unique Number

Find the first unique number in a stream

Easy

Logger Rate Limiter

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

Easy

Moving Average from Data Stream

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

Easy

Number of Recent Calls

Count requests in the last 3000 milliseconds

Easy

Time Needed to Buy Tickets

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

QuickSelect

Medium

Sort Colors

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

Heaps

Medium

Kth Largest Element in an Array

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

Binary Search

Easy

Search Insert Position

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

Medium

Search in Rotated Sorted Array

Find target in rotated sorted array using modified binary search

Medium

Find Peak Element

Find the peak element in a sorted array using binary search

Medium

Find Minimum in Rotated Sorted Array

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

Medium

Search in 2D Matrix

Find target in sorted 2D matrix using binary search

Easy

Binary Search

Search for a target value in a sorted array

Medium

Capacity To Ship Packages Within D Days

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

Medium

Find First and Last Position of Element in Sorted Array

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

Easy

Find First Occurrence

Find the first occurrence of a target in a sorted array

Hard

Find in Mountain Array

Find a target in a mountain array using binary search

Medium

Find K Closest Elements

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

Hard

Find K-th Smallest Pair Distance

Find the k-th smallest absolute difference among all pairs

Easy

Find Smallest Letter Greater Than Target

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

Easy

First Bad Version

Find the first bad version using binary search

Easy

Guess Number Higher or Lower

Guess a number between 1 and n using binary search

Medium

Koko Eating Bananas

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

Medium

Magnetic Force Between Two Balls

Maximize the minimum magnetic force between balls placed in baskets

Medium

Minimum Number of Days to Make m Bouquets

Find the minimum days to make m bouquets from the garden

Medium

Most Profit Assigning Work

Assign jobs to workers to maximize total profit

Medium

Search a 2D Matrix II

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

Medium

Search in Rotated Sorted Array II

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

Medium

Snapshot Array

Design an array supporting snapshots and queries on past states

Hard

Split Array Largest Sum

Split array into m subarrays to minimize the largest subarray sum

Medium

Time Based Key-Value Store

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

Easy

Valid Perfect Square

Determine if a number is a perfect square without using sqrt

Hard

Median of Two Sorted Arrays

Find the median of two sorted arrays using binary search partitioning

Medium

Random Pick with Weight

Pick an index with probability proportional to its weight using prefix sums

Backtracking

Medium

Subsets

Generate all subsets using recursive backtracking with decision tree

Medium

Permutations

Generate all permutations by choosing unused elements recursively

Medium

Combination Sum

Find all combinations that sum to a target using reusable elements

Medium

Combination Sum II

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

Medium

Combination Sum III

Find all combinations of k numbers that sum to n

Medium

Combinations

Generate all combinations of k numbers from 1 to n

Medium

Generate Parentheses

Generate all combinations of well-formed parentheses

Medium

Letter Combinations of a Phone Number

Generate all possible letter combinations from a phone number

Hard

N-Queens

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

Medium

Palindrome Partitioning

Partition a string into all possible palindrome substrings

Medium

Permutations II

Generate all unique permutations of a collection that may have duplicates

Medium

Restore IP Addresses

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

Medium

Subsets II

Generate all subsets of a collection that may have duplicates

Hard

Sudoku Solver

Solve a Sudoku puzzle by filling in the empty cells

Hard

Unique Paths III

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

Medium

Word Search

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

Hard

Word Squares

Build all word squares from a given set of words

Tree

Medium

Binary Tree Level Order Traversal

Traverse tree level by level using BFS and queue

Medium

Binary Tree Right Side View

Traverse tree right side view using BFS and queue

Medium

Binary Tree Zigzag Level Order Traversal

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

Medium

Populating Next Right Pointers in Each Node II

Connect nodes at same level using BFS with queue

Easy

Binary Tree Preorder Traversal

Traverse tree preorder using DFS and stack

Easy

Same Tree

Check if two binary trees are identical

Easy

Symmetric Tree

Check if a binary tree is symmetric

Easy

Binary Tree Paths

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

Easy

Convert Sorted Array to Binary Search Tree

Convert a sorted array to a binary search tree

Medium

Maximum Difference Between Node and Ancestor

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

Medium

Path Sum III

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

Easy

Binary Tree Inorder Traversal

Traverse tree inorder using DFS and stack

Easy

Minimum Distance Between BST Nodes

Find the minimum distance between any two nodes in a BST

Medium

Validate Binary Search Tree

Check if a binary tree satisfies BST properties using recursive DFS

Medium

Kth Smallest Element in a BST

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

Easy

Binary Tree Postorder Traversal

Traverse tree postorder using DFS and stack

Easy

Invert Binary Tree

Invert a binary tree using DFS and stack

Medium

Diameter of Binary Tree

Find the diameter of a binary tree using recursion

Medium

Lowest Common Ancestor of a Binary Tree

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

Medium

Find Duplicate Subtrees

Find duplicate subtrees in a binary tree using serialization

Medium

Flatten Binary Tree to Linked List

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

Medium

Distribute Coins in Binary Tree

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

Medium

House Robber III

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

Hard

Binary Tree Maximum Path Sum

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

Hard

Binary Tree Cameras

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

Easy

Average of Levels in Binary Tree

Return the average value of each level of a binary tree

Easy

Balanced Binary Tree

Determine if a binary tree is height-balanced

Medium

Boundary of Binary Tree

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

Medium

Check Completeness of a Binary Tree

Determine if a binary tree is a complete binary tree

Medium

Construct Binary Tree from Inorder and Postorder Traversal

Build a binary tree from its inorder and postorder traversals

Medium

Construct Binary Tree from Preorder and Inorder Traversal

Build a binary tree from its preorder and inorder traversals

Medium

Construct Quad Tree

Construct a quad tree from a 2D grid

Medium

Count Complete Tree Nodes

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

Medium

Count Good Nodes in Binary Tree

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

Medium

Delete Nodes And Return Forest

Delete nodes from a binary tree and return the remaining forest

Medium

Longest Univalue Path

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

Medium

Maximum Binary Tree

Construct a maximum binary tree from an array

Medium

Maximum Width of Binary Tree

Find the maximum width of a binary tree across all levels

Medium

Path Sum II

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

Medium

Populating Next Right Pointers in Each Node

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

Hard

Serialize and Deserialize Binary Tree

Encode a binary tree to a string and decode it back

Medium

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

Find the shortest path between two nodes in a binary tree

Easy

Subtree of Another Tree

Check if a tree is a subtree of another tree

Easy

Sum of Left Leaves

Find the sum of all left leaves in a binary tree

Medium

Sum Root to Leaf Numbers

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

Hard

Vertical Order Traversal of a Binary Tree

Traverse a binary tree column by column from left to right

BST

Medium

Trim Binary Search Tree

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

Medium

Balance a Binary Search Tree

Convert an unbalanced BST into a balanced BST

Medium

Binary Search Tree Iterator

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

Easy

Closest Binary Search Tree Value

Find the value in a BST closest to a given target

Medium

Construct BST from Preorder Traversal

Construct a BST from its preorder traversal

Medium

Convert BST to Sorted Doubly Linked List

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

Medium

Delete from BST

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

Medium

Delete Node in a BST

Delete a node in a BST and return the root

Medium

Inorder Successor in BST

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

Medium

Inorder Successor in BST II

Find the in-order successor when nodes have parent pointers

Easy

Insert into BST

Insert a value into a binary search tree

Medium

Insert into a Binary Search Tree

Insert a value into a BST and return the root

Medium

Largest BST Subtree

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

Easy

Lowest Common Ancestor of a BST

Find the lowest common ancestor of two nodes in a BST

Easy

Minimum Absolute Difference in BST

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

Easy

Range Sum of BST

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

Hard

Recover Binary Search Tree

Recover a BST where two nodes were swapped by mistake

Easy

Search in a Binary Search Tree

Find the node with the given value in a BST

Tries

Medium

Search Suggestions System

Generate product suggestions for each prefix using binary search

Hard

Word Search II

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

Medium

Design Add and Search Words Data Structure

Design a data structure that supports adding and searching with wildcards

Hard

Design In-Memory File System

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

Hard

Design Search Autocomplete System

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

Medium

Implement Trie

Implement a trie with insert, search, and startsWith operations

Medium

Implement Trie (Prefix Tree)

Implement a prefix tree supporting insert, search, and startsWith

Medium

Longest Word in Dictionary

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

Medium

Maximum XOR of Two Numbers in an Array

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

Medium

Replace Words

Replace words in a sentence with their root from a dictionary

Hard

Stream of Characters

Detect words from a dictionary in a stream of characters

Medium

Remove Sub-Folders from the Filesystem

Remove folders whose parent folder is also present in the list

Heap

Medium

Sort Characters By Frequency

Sort characters by frequency using min-heap

Medium

Furthest Building You Can Reach

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

Medium

Top K Frequent Elements

Find top k frequent elements using min-heap

Hard

Find Median from Data Stream

Find median from data stream using two heaps

Hard

IPO

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

Medium

K Closest Points to Origin

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

Medium

Find K Pairs with Smallest Sums

Find k pairs with smallest sums using min-heap

Hard

Merge k Sorted Lists

Merge k sorted lists using min-heap

Hard

All O'one Data Structure

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

Hard

Employee Free Time

Find the free time intervals for all employees

Easy

Kth Largest Element in a Stream

Find the kth largest element in a stream of numbers

Medium

Find the Kth Largest Integer in the Array

Find the kth largest integer in a string array

Easy

Last Stone Weight

Simulate smashing the two heaviest stones until one remains

Hard

LFU Cache

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

Hard

Maximum Performance of a Team

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

Medium

Minimum Cost to Connect Sticks

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

Hard

Minimum Cost to Hire K Workers

Hire exactly k workers with minimum total wage

Hard

Minimum Number of Refueling Stops

Find the minimum refueling stops to reach the target

Hard

Process Tasks Using Servers

Assign tasks to the smallest available server greedily

Medium

Single-Threaded CPU

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

Hard

The Skyline Problem

Find the skyline formed by a collection of buildings

Hard

Sliding Window Median

Find the median of each sliding window of size k

Hard

Smallest Range Covering Elements from K Lists

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

Medium

Stock Price Fluctuation

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

Medium

Task Scheduler

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

Medium

Top K Frequent Words

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

Medium

Two Best Non-Overlapping Events

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

Intervals

Medium

Merge Intervals

Merge all overlapping intervals on a timeline

Medium

Insert Interval

Insert a new interval into a list of intervals

Medium

Minimum Number of Arrows to Burst Balloons

Find minimum arrows needed to burst all balloons using greedy algorithm

Medium

Non-overlapping Intervals

Find maximum number of non-overlapping intervals using greedy algorithm

Medium

Kth Smallest Element in Sorted Matrix

Find kth smallest element using binary search on value range

Medium

Maximum Number of Events That Can Be Attended

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

Medium

Avoid Flood in The City

Prevent flooding by drying lakes before they overflow

Medium

Car Pooling

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

Medium

Heaters

Find the minimum heater radius to cover all houses

Medium

Interval List Intersections

Find the intersection of two lists of closed intervals

Easy

Meeting Rooms

Determine if a person can attend all meetings

Medium

Meeting Rooms II

Find the minimum number of conference rooms required

Hard

Meeting Rooms III

Find the room that held the most meetings

Medium

Meeting Scheduler

Find the earliest available slot for a meeting of given duration

Hard

Minimum Interval to Include Each Query

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

Medium

My Calendar I

Implement a calendar that books events without double-booking

Medium

My Calendar II

Implement a calendar allowing at most double-booking

Medium

Remove Covered Intervals

Remove intervals that are covered by another interval in the list

Hard

Set Intersection Size At Least Two

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

Greedy

Medium

Jump Game II

Find minimum jumps to reach the end using greedy BFS approach

Medium

Gas Station

Find starting gas station to complete circular route using greedy algorithm

Easy

Assign Cookies

Assign cookies to children to maximize the number of content children

Medium

Boats to Save People

Find the minimum number of boats to carry all people

Hard

Candy

Distribute candy to children with minimum total using ratings

Medium

Jump Game

Determine if you can reach the last index from the first

Medium

Jump Game VII

Determine if you can reach the last index using jump constraints

Medium

Longest Happy String

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

Medium

Maximum Matrix Sum

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

Medium

Minimum Deletions to Make Character Frequencies Unique

Find the minimum deletions to make all character frequencies unique

Medium

Partition Labels

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

Medium

Queue Reconstruction by Height

Reconstruct a queue based on people's heights and counts

Medium

Split Array into Consecutive Subsequences

Split an array into consecutive subsequences of at least length 3

Graph

Medium

Depth First Search

Traverse a graph using Depth First Search

Medium

Number of Islands

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

Medium

Time Needed to Inform All Employees

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

Medium

Employee Importance

Find the importance of an employee using DFS with memoization

Medium

Clone Graph

Clone a graph using DFS

Medium

Is Graph Bipartite?

Check if a graph is bipartite using DFS with coloring

Medium

All Nodes Distance K in Binary Tree

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

Medium

Rotting Oranges

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

Hard

Word Ladder

Find shortest word transformation sequence using BFS

Medium

Course Schedule II

Find valid course order using DFS topological sort on prerequisite graph

Medium

Find Eventual Safe States

Find eventual safe states in a graph using DFS

Medium

Minimum Height Trees

Find minimum height trees in a graph using BFS

Medium

Number of Provinces

Count connected components in adjacency matrix using DFS

Medium

Redundant Connection

Find redundant connection in a graph using Union-Find

Hard

Minimize Malware Spread

Find redundant connection in a graph using Union-Find

Medium

Course Schedule IV

Check prerequisite relationships using BFS topological sort with ancestor sets

Medium

Parallel Courses

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

Easy

Flood Fill

Paint connected pixels with new color using recursive DFS

Medium

Number of Distinct Islands

Count distinct island shapes using DFS with path signatures

Medium

Find All Possible Recipes

Find makeable recipes using BFS from supplies through ingredient graph

Hard

Sort Items by Groups

Sort items respecting group and dependency constraints using dual topological sort

Hard

Alien Dictionary

Derive character ordering from sorted alien words using topological sort

Medium

Connected Components

Count connected components in undirected graph using Union-Find

Medium

Surrounded Regions

Capture surrounded O regions using DFS

Medium

Graph Valid Tree

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

Medium

Accounts Merge

Merge accounts with common emails using Union-Find

Medium

Evaluate Division

Evaluate variable division queries using weighted Union-Find

Medium

Most Stones Removed

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

Hard

Number of Islands II

Count islands after each addLand operation using online Union-Find

Hard

Critical Connections in a Network

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

Hard

Longest Path With Different Adjacent Characters

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

Medium

01 Matrix

Find distance to nearest zero using multi-source BFS

Medium

Walls and Gates

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

Medium

Open the Lock

Find minimum turns to open lock using BFS on combinations

Medium

Snakes and Ladders

Find minimum moves on board game using BFS

Medium

Minimum Genetic Mutation

Find minimum gene mutations using BFS on gene strings

Medium

Minimum Knight Moves

Find minimum knight moves to target using BFS

Medium

Shortest Path in Binary Matrix

Find shortest clear path using 8-directional BFS

Medium

Path With Maximum Minimum Value

Find path maximizing minimum value using binary search + BFS

Hard

Shortest Path with Obstacles Elimination

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

Hard

Bus Routes

Find minimum buses to reach destination using BFS on routes

Hard

Minimum Obstacle Removal to Reach Corner

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

Medium

Cheapest Flights Within K Stops

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

Medium

Path with Maximum Probability

Find path with maximum success probability using modified Dijkstra

Medium

Path With Minimum Effort

Find path minimizing maximum absolute height difference using Dijkstra

Medium

The Maze II

Find shortest distance in a maze with rolling ball using BFS

Medium

Minimum Cost to Convert String I

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

Medium

Find Minimum Time to Reach Last Room I

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

Hard

Swim in Rising Water

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

Hard

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

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

Hard

Minimum Weighted Subgraph With the Required Paths

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

Medium

Min Cost to Connect All Points

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

Medium

Connecting Cities With Minimum Cost

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

Hard

Optimize Water Distribution in a Village

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

Hard

Cracking the Safe

Find shortest string containing all codes using de Bruijn sequence

Hard

Valid Arrangement of Pairs

Find valid pair arrangement using Hierholzer's Eulerian path algorithm

Hard

A* Search Algorithm

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

Medium

All Paths From Source to Target

Find all paths from source to target in a DAG

Medium

Bellman-Ford Algorithm

Find shortest paths from a source, handling negative weights

Easy

Breadth First Search

Traverse a graph level by level using a queue

Hard

Centroid Decomposition

Decompose a tree by repeatedly finding and removing centroids

Hard

Find Critical and Pseudo-Critical Edges in MST

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

Medium

Detect Cycle in Directed Graph

Detect a cycle in a directed graph using DFS

Medium

Detect Cycle in Undirected Graph

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

Medium

Dijkstra's Algorithm

Find shortest paths from a source in a weighted graph

Hard

Floyd-Warshall Algorithm

Find all-pairs shortest paths in a weighted graph

Hard

Heavy-Light Decomposition

Decompose a tree for efficient path queries

Hard

Kosaraju's SCC Algorithm

Find all strongly connected components in a directed graph

Medium

Kruskal's MST Algorithm

Find a minimum spanning tree using Kruskal's greedy approach

Hard

Making A Large Island

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

Medium

Maximize Spanning Tree Stability

Find the spanning tree that maximizes the minimum edge weight

Medium

Network Delay Time

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

Medium

Number of Connected Components in an Undirected Graph

Count connected components in an undirected graph

Medium

Number of Enclaves

Count land cells that cannot reach the boundary

Medium

Pacific Atlantic Water Flow

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

Medium

Prim's MST Algorithm

Find a minimum spanning tree using Prim's greedy approach

Hard

Reconstruct Itinerary

Find a valid itinerary using all tickets in lexicographic order

Hard

Tarjan's Algorithm

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

Medium

Topological Sort

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

Medium

Union-Find (Disjoint Set Union)

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

Dynamic Programming

Medium

Longest Increasing Subsequence

Find the length of the longest increasing subsequence

Medium

Minimum Path Sum

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

Hard

Russian Doll Envelopes

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

Easy

Climbing Stairs

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

Easy

Min Cost Climbing Stairs

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

Medium

House Robber

Find maximum money to rob from houses using dynamic programming

Medium

House Robber II

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

Medium

Unique Paths II

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

Medium

Count Square Submatrices with All Ones

Find number of square submatrices with all ones using dynamic programming

Medium

Maximum Number of Points with Cost

Find maximum number of points with cost using dynamic programming

Hard

Burst Balloons

Find maximum number of points with cost using dynamic programming

Hard

Maximum Profit in Job Scheduling

Find maximum profit in job scheduling using dynamic programming

Medium

Longest Common Subsequence

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

Medium

Edit Distance

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

Medium

Longest Palindromic Subsequence

Find length of longest palindromic subsequence using dynamic programming

Medium

Decode Ways

Find number of ways to decode a string using dynamic programming

Hard

Wildcard Matching

Check if one string matches the pattern using dynamic programming

Hard

Distinct Subsequences

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

Medium

Coin Change

Find minimum number of coins to make amount using dynamic programming

Medium

Coin Change II

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

Medium

Perfect Squares

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

Medium

Partition Equal Subset Sum

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

Medium

Target Sum

Find number of ways to target sum using dynamic programming

Medium

Last Stone Weight II

Find the minimum weight of the last stone using dynamic programming

Medium

Triangle

Find minimum path sum in a triangle using dynamic programming

Easy

Fibonacci Number

Compute the nth Fibonacci number using space-optimized DP

Medium

Maximum Length of Pair Chain

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

Medium

Delete and Earn

Maximize points by deleting numbers using house-robber style DP

Medium

Integer Break

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

Medium

Greatest Sum Divisible by Three

Find maximum sum divisible by 3 using remainder DP

Hard

Number of Ways to Paint N × 3 Grid

Count grid painting ways using pattern transition DP

Medium

Ones and Zeroes

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

Hard

Profitable Schemes

Count schemes meeting profit threshold using 2D knapsack DP

Medium

Minimum Cost For Tickets

Find minimum cost for travel days using DP with ticket passes

Medium

Number of Longest Increasing Subsequence

Count the number of longest increasing subsequences using DP

Medium

Longest String Chain

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

Medium

Longest Arithmetic Subsequence

Find the longest arithmetic subsequence using hash map DP

Easy

Pascal's Triangle

Generate Pascal's triangle row by row using dynamic programming

Medium

Unique Paths

Count unique paths in a grid using space-optimized DP

Medium

Maximal Square

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

Medium

Paint House

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

Medium

Minimum Falling Path Sum

Find minimum sum falling path through a matrix using DP

Hard

Remove Boxes

Maximize points by removing boxes using 3D memoization DP

Hard

Maximal Rectangle

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

Hard

Cherry Pickup

Collect maximum cherries with two walkers using simultaneous DP

Hard

Dungeon Game

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

Hard

Longest Increasing Path in a Matrix

Find longest increasing path using BFS topological sort

Hard

Painting a Grid With Three Different Colors

Count grid colorings using state transition matrix exponentiation

Hard

Minimum Cost Path with Teleportations

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

Hard

Frog Jump

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

Hard

Optimal Account Balancing

Find minimum transfers to settle debts using bitmask subset DP

Hard

Minimum Difficulty of a Job Schedule

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

Hard

Minimum Cost to Cut a Stick

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

Medium

Word Break

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

Medium

Interleaving String

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

Medium

Minimum Deletions to Make String Balanced

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

Hard

Word Break II

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

Hard

Regular Expression Matching

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

Hard

Palindrome Partitioning II

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

Hard

Strange Printer

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

Hard

Shortest Common Supersequence

Build shortest supersequence of two strings using LCS DP with traceback

Medium

Unique Binary Search Trees II

Generate all structurally unique BSTs using bottom-up interval DP

Medium

Number of Ways to Arrive at Destination

Find the number of shortest paths using Dijkstra with counting

Hard

Sum of Distances in Tree

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

Medium

Campus Bikes II

Assign workers to bikes minimizing total distance using bitmask DP

Medium

Partition to K Equal Sum Subsets

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

Medium

Minimum Number of Work Sessions

Find minimum work sessions using subset DP with session time constraint

Medium

Fair Distribution of Cookies

Distribute cookies among children minimizing unfairness using bitmask DP

Hard

Shortest Path Visiting All Nodes

Find shortest path visiting all nodes using BFS with bitmask DP

Medium

Count Numbers with Unique Digits

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

Hard

Number of Digit One

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

Hard

Numbers At Most N Given Digit Set

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

Medium

Knight Probability in Chessboard

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

Medium

Soup Servings

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

Medium

New 21 Game

Find probability of score ≤ n using sliding window DP

Medium

Best Time to Buy and Sell Stock with Cooldown

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

Medium

Best Time to Buy and Sell Stock with Transaction Fee

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

Hard

Best Time to Buy and Sell Stock III

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

Hard

Best Time to Buy and Sell Stock IV

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

Medium

Longest Palindromic Substring

Find the longest palindromic substring using dynamic programming

Hard

Concatenated Words

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

Hard

Constrained Subsequence Sum

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

Hard

Count of Range Sum

Count range sums that lie in a given interval

Medium

Number of People Aware of a Secret

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

BIT / Segment Tree

Medium

Range Sum Query - Mutable

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

Medium

Range Sum Query 2D - Mutable

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

Hard

Count of Smaller Numbers After Self

Count smaller elements to the right using a Binary Indexed Tree

Hard

Falling Squares

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

Hard

Block Placement Queries

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

Hard

Longest Balanced Subarray II

Find the longest balanced subarray using a Lazy Segment Tree

Hard

Number of Pairs Satisfying Inequality

Count valid pairs using a Binary Indexed Tree on difference array

Medium

Fenwick Tree (Binary Indexed Tree)

Efficient data structure for prefix sum queries and point updates

Hard

Range Module

Track ranges of numbers and query if a range is covered

Medium

Range Sum Query 2D - Immutable

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

Easy

Range Sum Query - Immutable

Answer range sum queries on an immutable array using prefix sums

Hard

Reverse Pairs

Count important reverse pairs using merge sort or BIT

Medium

Segment Tree

Build a segment tree for range sum queries and point updates

Hard

Segment Tree with Lazy Propagation

Handle range updates efficiently using lazy propagation in segment trees

Medium

Sparse Table

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

Medium

Sqrt Decomposition

Answer range queries using square root decomposition

Math & Geometry

Easy

Palindrome Number

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

Medium

Reverse Integer

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

Medium

Factorial Trailing Zeroes

Count trailing zeroes in n! by counting factors of 5

Medium

Valid Square

Determine if four points form a valid square using pairwise distances

Medium

Minimum Area Rectangle II

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

Hard

Max Points on a Line

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

Hard

Perfect Rectangle

Determine if rectangles form an exact cover of a rectangular region

Medium

Pow(x, n)

Implement fast exponentiation using repeated squaring

Hard

Rectangle Area II

Find the total area covered by a list of rectangles

Math / Geometry

Medium

Multiply Strings

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

Medium

Find the Duplicate Number

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

Medium

Count Good Numbers

Count good digit strings using binary exponentiation

Medium

Count Primes

Count primes less than n using the Sieve of Eratosthenes

Medium

Valid Triangle Number

Count valid triangles using sorting and two pointers

Hard

Minimum Area Rectangle

Find the minimum area rectangle from a set of points

Math

Easy

Plus One

Increment a number represented as an array of digits

Easy

Roman to Integer

Convert a Roman numeral string to an integer

Easy

Excel Sheet Column Title

Convert a column number to its Excel column title

Easy

Greatest Common Divisor of Strings

Find the largest string that divides both input strings

Easy

Ugly Number

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

Medium

Ugly Number II

Find the nth ugly number using three pointers

Medium

Find the Winner of the Circular Game

Find the winner of Josephus-style elimination game

645 of 645 algorithms shown