Leetcode

Jul 01, 2025 • Leetcode

Binary Tree Maximum Path Sum

A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them

May 16, 2025 • Leetcode

Path Sum

Given the root of a binary tree and an integer targetSum, return true if the tree has a root-to-leaf path.

May 02, 2025 • Leetcode

Merge Two Sorted Lists

You are given the heads of two sorted linked lists list1 and list2.

Aug 15, 2025 • Leetcode

Pacific Atlantic Water Flow

There is an m x n rectangular island that borders both the Pacific Ocean and Atlantic Ocean.

May 23, 2025 • Leetcode

Binary Tree Paths

Given the root of a binary tree, return all root-to-leaf paths in any order.

Jun 21, 2025 • Leetcode

Nth Digit

Given an integer n, return the nth digit of the infinite integer sequence [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ...].

Jun 05, 2025 • Leetcode

Trim a Binary Search Tree

Given the root of a binary search tree and the lowest and highest boundaries as low and high

Apr 04, 2025 • Leetcode

204. Count Primes

Given an integer n, return the number of prime numbers that are strictly less than n.

Jul 20, 2025 • Leetcode

Repeated DNA Sequences

The DNA sequence is composed of a series of nucleotides abbreviated as 'A', 'C', 'G', and 'T'.

May 09, 2025 • Leetcode

Ugly Number

An ugly number is a positive integer which does not have a prime factor other than 2, 3, and 5.

Apr 30, 2025 • Leetcode

Diagonal Traverse

Given an m x n matrix mat, return an array of all the elements of the array in a diagonal order.

May 05, 2025 • Leetcode

Gas Station

There are n gas stations along a circular route, where the amount of gas at the ith station is gas[i].

Apr 12, 2025 • Leetcode

Group Anagrams

Given an array of strings strs, group the anagrams together. You can return the answer in any order.

Apr 27, 2025 • Leetcode

Longest Consecutive Sequence

Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.

Jul 25, 2025 • Leetcode

Evaluate Reverse Polish Notation

You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation.

Apr 03, 2025 • Leetcode

207 Course Schedule

There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1

Aug 22, 2025 • Leetcode

Repeated Substring Pattern

Given a string s, check if it can be constructed by taking a substring of it and appending multiple copies of the substring together.

Jul 24, 2025 • Leetcode

Sort Characters By Frequency

Given a string s, sort it in decreasing order based on the frequency of the characters.

May 26, 2025 • Leetcode

Univalued Binary Tree

A binary tree is uni-valued if every node in the tree has the same value.

Mar 19, 2025 • Leetcode

152. Maximum Product Subarray

Given an integer array nums, find a subarray that has the largest product, and return the product.

May 14, 2025 • Leetcode

Balanced Binary Tree

Given a binary tree, determine if it is height-balanced.

Aug 18, 2025 • Leetcode

My Calendar III

A k-booking happens when k events have some non-empty intersection (i.e., there is some time that is common to all k events.)

May 01, 2025 • Leetcode

Escape The Ghosts

You are playing a simplified PAC-MAN game on an infinite 2-D grid. You start at the point

Aug 08, 2025 • Leetcode

Count Numbers with Unique Digits

Given an integer n, return the count of all numbers with unique digits, x, where 0 <= x < 10n.

Jul 31, 2025 • Leetcode

Longest Substring Without Repeating Characters

Given a string s, find the length of the longest substring without duplicate characters.

Mar 16, 2025 • Leetcode

Maximize Distance to Closest Person

You are given an array representing a row of seats where seats[i] = 1 represents a person sitting in the ith seat, and seats[i] = 0 represents that the ith.

Jun 08, 2025 • Leetcode

Find Mode in Binary Search Tree

Given the root of a binary search tree (BST) with duplicates, return all the mode(s) (i.e., the most frequently occurred element) in it.

Jun 23, 2025 • Leetcode

Divide Two Integers

Given two integers dividend and divisor, divide two integers without using multiplication, division, and mod operator.

Jul 02, 2025 • Leetcode

Maximum Width of Binary Tree

Given the root of a binary tree, return the maximum width of the given tree.

Apr 07, 2025 • Leetcode

461 Hamming Distance

The Hamming distance between two integers is the number of positions at which the corresponding bits are different.

Jun 30, 2025 • Leetcode

Construct Binary Tree from Preorder and Inorder Traversal

Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree

Jul 22, 2025 • Leetcode

License Key Formatting

You are given a license key represented as a string s that consists of only alphanumeric characters and dashes

Jul 18, 2025 • Leetcode

Number of Islands

Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands.

Jun 27, 2025 • Leetcode

Best Time to Buy and Sell Stock with Transaction Fee

You are given an array prices where prices[i] is the price of a given stock on the ith day, and an integer fee representing a transaction fee.

Jun 13, 2025 • Leetcode

My Calendar I

You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a double booking.

Apr 01, 2025 • Leetcode

35. Search Insert Position

Given a sorted array of distinct integers and a target value, return the index if the target is found. If not, return the index where it would be if it were.

Apr 19, 2025 • Leetcode

Detect Capital

We define the usage of capitals in a word to be right when one of the following cases holds:

May 07, 2025 • Leetcode

Queue Reconstruction by Height

You are given an array of people, people, which are the attributes of some people in a queue (not necessarily in order)

May 19, 2025 • Leetcode

Minimum Depth of Binary Tree

Given a binary tree, find its minimum depth.

Aug 09, 2025 • Leetcode

Regular Expression Matching

Given an input string s and a pattern p, implement regular expression matching with support for '.' and '*' where:

Jun 10, 2025 • Leetcode

Validate Binary Search Tree

Given the root of a binary tree, determine if it is a valid binary search tree (BST).

May 15, 2025 • Leetcode

Maximum Depth of Binary Tree

Given the root of a binary tree, return its maximum depth.

Apr 21, 2025 • Leetcode

Add Strings

Given two non-negative integers, num1 and num2 represented as string, return the sum of num1 and num2 as a string.

Aug 02, 2025 • Leetcode

Substring with Concatenation of All Words

You are given a string s and an array of strings words. All the strings of words are of the same length.

Mar 20, 2025 • Leetcode

239. Sliding Window Maximum

You are given an array of integers nums, there is a sliding window of size k.

Mar 26, 2025 • Leetcode

91. Decode Ways

A message containing letters from A-Z is being encoded to numbers using the following mapping.

Jul 30, 2025 • Leetcode

Partition Equal Subset Sum

Given an integer array nums, return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false

May 03, 2025 • Leetcode

Rotate List

Given the head of a linked list, rotate the list to the right by k places.

Apr 23, 2025 • Leetcode

First Unique Character in a String

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

Jul 14, 2025 • Leetcode

Partition List

Given the head of a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.

Aug 10, 2025 • Leetcode

Permutations II

Given a collection of numbers, nums, that might contain duplicates, return all possible unique permutations in any order.

Aug 06, 2025 • Leetcode

Minimum Window Substring

Given two strings s and t of lengths m and n respectively, return the minimum window substring

May 30, 2025 • Leetcode

Kth Smallest Element in a BST

Given the root of a binary search tree, and an integer k, return the kth smallest value (1-indexed) of all the values of the nodes in the tree.

Apr 02, 2025 • Leetcode

367 Valid Perfect Square

Given a positive integer num, return true if num is a perfect square or false otherwise.

Jun 22, 2025 • Leetcode

Total Hamming Distance

The Hamming distance between two integers is the number of positions at which the corresponding bits are different.

Apr 11, 2025 • Leetcode

Add Binary

Given two binary strings a and b, return their sum as a binary string.

Jul 21, 2025 • Leetcode

Longest Continuous Increasing Subsequence

Given an unsorted array of integers nums, return the length of the longest continuous increasing subsequence (i.e. subarray).

Jun 26, 2025 • Leetcode

Ugly Number II

An ugly number is a positive integer whose prime factors are limited to 2, 3, and 5.

Jun 09, 2025 • Leetcode

Different Ways to Add Parentheses

Given a string expression of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators.

Jul 10, 2025 • Leetcode

Letter Combinations of a Phone Number

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent

Apr 22, 2025 • Leetcode

Compare Version Numbers

Given two version strings, version1 and version2, compare them. A version string consists of revisions separated by dots '.'. The value of the revision.

Jul 08, 2025 • Leetcode

Candy

There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings.

Jun 07, 2025 • Leetcode

Second Minimum Node In a Binary Tree

Given a non-empty special binary tree consisting of nodes with the non-negative value.

Jul 03, 2025 • Leetcode

Lowest Common Ancestor of a Binary Search Tree

Given a binary search tree (BST), find the lowest common ancestor (LCA) node of two given nodes in the BST.

Aug 19, 2025 • Leetcode

Find First and Last Position of Element in Sorted Array

Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

May 20, 2025 • Leetcode

Diameter of Binary Tree

Given the root of a binary tree, return the length of the diameter of the tree.

Apr 28, 2025 • Leetcode

Delete Operation for Two Strings

Given two strings word1 and word2, return the minimum number of steps required to make word1 and word2 the same.

May 06, 2025 • Leetcode

Jump Game

You are given an integer array nums. You are initially positioned at the array's first index, and each element in the array represents your maximum jump length.

Apr 09, 2025 • Leetcode

Reverse Integer

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range.

Aug 01, 2025 • Leetcode

Search a 2D Matrix II

Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties

Apr 13, 2025 • Leetcode

Count and Say

The count-and-say sequence is a sequence of digit strings defined by the recursive formula

Jul 13, 2025 • Leetcode

Reverse Nodes in k-Group

Given the head of a linked list, reverse the nodes of the list k at a time, and return the modified list.

Apr 08, 2025 • Leetcode

554 Brick Wall

There is a rectangular brick wall in front of you with n rows of bricks. The ith row has some number of bricks each of the same height (i.e., one unit)

Jun 17, 2025 • Leetcode

Restore IP Addresses

A valid IP address consists of exactly four integers separated by single dots. Each integer is between.

Jun 15, 2025 • Leetcode

Binary Tree Right Side View

Given the root of a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

Apr 25, 2025 • Leetcode

Bulls and Cows

You are playing the Bulls and Cows game with your friend.

May 24, 2025 • Leetcode

Convert Sorted Array to Binary Search Tree

Given an integer array nums where the elements are sorted in ascending order, convert it to a height-balanced binary search tree.

Mar 25, 2025 • Leetcode

2. Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers.

Jul 09, 2025 • Leetcode

Letter Case Permutation

Given a string s, you can transform every letter individually to be lowercase or uppercase to create another string.

Apr 18, 2025 • Leetcode

Binary Watch

A binary watch has 4 LEDs on the top to represent the hours (0-11), and 6 LEDs on the bottom to represent the minutes (0-59). Each LED represents a zero or one.

Jul 06, 2025 • Leetcode

Minimum Number of Arrows to Burst Balloons

There are some spherical balloons taped onto a flat wall that represents the XY-plane

Aug 21, 2025 • Leetcode

Shortest Completing Word

Given a string licensePlate and an array of strings words, find the shortest completing word in words.

Jul 27, 2025 • Leetcode

Min Cost Climbing Stairs

You are given an integer array cost where cost[i] is the cost of ith step on a staircase.

May 22, 2025 • Leetcode

Find Bottom Left Tree Value

Given the root of a binary tree, return the leftmost value in the last row of the tree.

Jun 19, 2025 • Leetcode

Keys and Rooms

There are n rooms labeled from 0 to n 1 and all the rooms are locked except for room

Jul 29, 2025 • Leetcode

My Calendar II

You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a triple booking.

Mar 28, 2025 • Leetcode

62. Unique Paths

There is a robot on an m x n grid. The robot is initially located at the top-left corner.

Mar 16, 2025 • Leetcode

Letter Combinations of a Phone Number Problem

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.

Aug 16, 2025 • Leetcode

Find K Closest Elements

Given a sorted integer array arr, two integers k and x, return the k closest integers to x in the array. The result should also be sorted in ascending order.

May 13, 2025 • Leetcode

Gray Code

An n-bit gray code sequence is a sequence of 2n integers where:

May 31, 2025 • Leetcode

Subtree of Another Tree

Given the roots of two binary trees root and subRoot, return true if there is a subtree of root with the same structure and node values of subRoot and false.

Jun 06, 2025 • Leetcode

Binary Tree Level Order Traversal

Given the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level).

Aug 17, 2025 • Leetcode

Heaters

Winter is coming! During the contest, your first job is to design a standard heater with a fixed warm radius to warm all the houses.

Jul 07, 2025 • Leetcode

Best Time to Buy and Sell Stock with Cooldown

You are given an array prices where prices[i] is the price of a given stock on the ith day.

Apr 06, 2025 • Leetcode

221 Maximal Square

Given an m x n binary matrix filled with 0's and 1's, find the largest square containing only 1's and return its area.

Aug 13, 2025 • Leetcode

Minesweeper

Let's play the minesweeper game (Wikipedia, online game)!

Jul 05, 2025 • Leetcode

Insertion Sort List

Given the head of a singly linked list, sort the list using insertion sort, and return the sorted list's head.

Jun 24, 2025 • Leetcode

Search in Rotated Sorted Array

There is an integer array nums sorted in ascending order (with distinct values).

Jun 14, 2025 • Leetcode

Redundant Connection

In this problem, a tree is an undirected graph that is connected and has no cycles.

Jun 18, 2025 • Leetcode

Generate Parentheses

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

Jun 04, 2025 • Leetcode

Maximum Binary Tree

You are given an integer array nums with no duplicates. A maximum binary tree can be built recursively from nums using the following algorithm.

Apr 23, 2025 • Leetcode

Isomorphic Strings

Given two strings s and t, determine if they are isomorphic.

Aug 14, 2025 • Leetcode

Maximum Average Subarray I

You are given an integer array nums consisting of n elements, and an integer k

Mar 22, 2025 • Leetcode

526. Beautiful Arrangement

Suppose you have n integers labeled 1 through n. A permutation of those n integers.

Jun 12, 2025 • Leetcode

Maximal Rectangle

Given a rows x cols binary matrix filled with 0's and 1's, find the largest rectangle containing

Jul 16, 2025 • Leetcode

Split Linked List in Parts

Given the head of a singly linked list and an integer k, split the linked list into k consecutive linked list parts.

Jul 15, 2025 • Leetcode

Remove Duplicates from Sorted List

Given the head of a sorted linked list

Aug 11, 2025 • Leetcode

Partition to K Equal Sum Subsets

Given an integer array nums and an integer k, return true if it is possible to divide this array into k non-empty subsets whose sums are all equal.

Mar 30, 2025 • Leetcode

50. Pow(x, n)

Implement pow(x, n), which calculates x raised to the power n (i.e., xn).

Mar 31, 2025 • Leetcode

69. Sqrt(x)

Given a non-negative integer x, return the square root of x rounded down to the nearest intege.

Apr 20, 2025 • Leetcode

Magical String

A magical string s consists of only '1' and '2' and obeys the following rules

May 10, 2025 • Leetcode

Sum of Square Numbers

Given a non-negative integer c, decide whether there're two integers a and b such that a2 + b2 = c.

Apr 16, 2025 • Leetcode

Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings.

Apr 10, 2025 • Leetcode

Best Time to Buy and Sell Stock

You are given an array prices where prices[i] is the price of a given stock on the ith day.

Aug 03, 2025 • Leetcode

Minimum Height Trees

A tree is an undirected graph in which any two vertices are connected by exactly one path. In other words, any connected graph without simple cycles is a tree.

Jun 11, 2025 • Leetcode

First Missing Positive

Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums.

Mar 18, 2025 • Leetcode

581. Shortest Unsorted Continuous Subarray

Given an integer array nums, you need to find one continuous subarray such that if you only sort this subarray in non-decreasing order.

Aug 07, 2025 • Leetcode

Backspace String Compare

Given two strings s and t, return true if they are equal when both are typed into empty text editors.

Jun 28, 2025 • Leetcode

Binary Tree Zigzag Level Order Traversal

Given the root of a binary tree, return the zigzag level order traversal of its nodes' values. (i.e., from left to right, then right to left for the next level

May 04, 2025 • Leetcode

Remove Nth Node From End of List

Given the head of a linked list, remove the nth node from the end of the list and return its head.

Mar 23, 2025 • Leetcode

394. Decode String

The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is being repeated exactly k

Jun 29, 2025 • Leetcode

Most Frequent Subtree Sum

Given the root of a binary tree, return the most frequent subtree sum. If there is a tie, return all the values with the highest frequency in any order.

May 08, 2025 • Leetcode

Roman to Integer

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Aug 11, 2025 • Leetcode

N-Queens II

The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other.

Mar 16, 2025 • Leetcode

Two Sum Problem

LeetCode Problem 1. Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

May 18, 2025 • Leetcode

Binary Tree Inorder Traversal

Given the root of a binary tree, return the inorder traversal of its nodes' values.

Apr 15, 2025 • Leetcode

Repeated String Match

Given two strings a and b, return the minimum number of times you should repeat string a so that string b is a substring of it.

Jun 20, 2025 • Leetcode

Factorial Trailing Zeroes

Given an integer n, return the number of trailing zeroes in n.

Jun 03, 2025 • Leetcode

Smallest Subtree with all the Deepest Nodes

Given the root of a binary tree, the depth of each node is the shortest distance to the root.

May 27, 2025 • Leetcode

Longest Univalue Path

Given the root of a binary tree, return the length of the longest path, where each node in the path has the same value. This path may or may not pass through.

Jul 23, 2025 • Leetcode

Buddy Strings

Given two strings s and goal, return true if you can swap two letters in s so the result is equal to goal

May 29, 2025 • Leetcode

Delete Node in a BST

Given a root node reference of a BST and a key, delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST.

Aug 12, 2025 • Leetcode

Expression Add Operators

Given a string num that contains only digits and an integer target, return all possibilities to insert the binary operators

Mar 24, 2025 • Leetcode

794. Valid Tic-Tac-Toe State

Given a Tic-Tac-Toe board as a string array board, return true if and only if it is possible to reach

Apr 24, 2025 • Leetcode

Robot Return to Origin

There is a robot starting at the position (0, 0), the origin, on a 2D plane. Given a sequence of its moves, judge if this robot ends up at (0, 0).

Aug 04, 2025 • Leetcode

Single Number II

Given an integer array nums where every element appears three times except for one, which appears exactly once

Apr 29, 2025 • Leetcode

Perfect Squares

Given an integer n, return the least number of perfect square numbers that sum to n.

Apr 17, 2025 • Leetcode

Longest Palindrome

Given a string s which consists of lowercase or uppercase letters, return the length of the longest palindrome that can be built with those letters.

Aug 05, 2025 • Leetcode

Random Pick with Weight

You are given a 0-indexed array of positive integers w where w[i] describes the weight of the ith index.

Jun 16, 2025 • Leetcode

Excel Sheet Column Title

Given an integer column Number, return its corresponding column title as it appears in an Excel sheet.

May 28, 2025 • Leetcode

Binary Tree Postorder Traversal

Given the root of a binary tree, return the postorder traversal of its nodes' values.

Jul 28, 2025 • Leetcode

Rotate Image

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

Jun 01, 2025 • Leetcode

Sum Root to Leaf Numbers

You are given the root of a binary tree containing digits from 0 to 9 only.

Jun 02, 2025 • Leetcode

Find Largest Value in Each Tree Row

Given the root of a binary tree, return an array of the largest value in each row of the tree (0-indexed).

Jul 19, 2025 • Leetcode

Remove Linked List Elements

Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head.

Apr 05, 2025 • Leetcode

542 Matrix

Given an m x n binary matrix mat, return the distance of the nearest 0 for each cell.

Aug 20, 2025 • Leetcode

The Skyline Problem

A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance

Jul 04, 2025 • Leetcode

Verify Preorder Serialization of a Binary Tree

One way to serialize a binary tree is to use preorder traversal. When we encounter a non-null node, we record the node's value. If it is a null node, we record.

Jul 17, 2025 • Leetcode

Linked List Cycle II

Given the head of a linked list, return the node where the cycle begins. If there is no cycle, return null.

Apr 26, 2025 • Leetcode

Rotated Digits

An integer x is a good if after rotating each digit individually by 180 degrees, we get a valid number that is different from x. Each digit must be rotated.

Jun 25, 2025 • Leetcode

Power of Four

Given an integer n, return true if it is a power of four. Otherwise, return false.

May 11, 2025 • Leetcode

Combination Sum

Given an array of distinct integers candidates and a target integer target.

Jul 11, 2025 • Leetcode

Linked List Components

You are given the head of a linked list containing unique integer values and an integer array nums that is a subset

May 17, 2025 • Leetcode

Same Tree

Given the roots of two binary trees p and q, write a function to check if they are the same or not.

Mar 21, 2025 • Leetcode

318. Maximum Product of Word Lengths

Given a string array words, return the maximum value of length(word[i]) * length(word[j])

Mar 27, 2025 • Leetcode

120. Triangle

Given a triangle array, return the minimum path sum from top to bottom

May 25, 2025 • Leetcode

Lowest Common Ancestor of a Binary Tree

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

May 21, 2025 • Leetcode

Convert BST to Greater Tree

Given the root of a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus the sum.

May 12, 2025 • Leetcode

Permutations

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.

Apr 14, 2025 • Leetcode

Valid Parentheses

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.