Given an array of integers, return indices of the two numbers such that they add up to a specific target.

Given two strings s and t, return true if t is an anagram of s, and false otherwise.

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

Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i].

Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k.

Given an array of n + 1 integers where each integer is in the range [1, n], find the one repeated number without modifying the array and using only O(1) space.

Given an array nums of size n, return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array.

Given an integer array nums, move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array.

Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.

Merge nums2 into nums1 as one sorted array. nums1 has enough space (size m + n) to hold additional elements from nums2.

Given an unsorted integer array nums, return the smallest missing positive integer. Must run in O(n) time and O(1) auxiliary space.

Given an integer array nums, return an integer array counts where counts[i] is the number of smaller elements to the right of nums[i].

Given an m x n grid of characters board and a string word, return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once.

Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum to target.

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

Given an integer array nums of unique elements, return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order.

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

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix.

Given the array nums after the possible rotation and an integer target, return the index of target if it is in nums, or -1 if it is not in nums.

Suppose an array of length n sorted in ascending order is rotated between 1 and n times. Find the minimum element of this array.

Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom.

Given an n x n matrix where each of the rows and columns is sorted in ascending order, return the kth smallest element in the matrix. Note that it is the kth smallest element in the sorted order, not the kth distinct element.

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

Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class with get(key) returning the value or -1 if not found, and put(key, value) to insert or update. When capacity is exceeded, evict the least recently used key.

You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

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

Given a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words.

You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins, return -1.

Given an integer array nums, return the length of the longest strictly increasing subsequence.

A message containing letters from A-Z can be encoded into numbers using the mapping: 'A' -> "1", 'B' -> "2", ... 'Z' -> "26". To decode an encoded message, all the digits must be grouped then mapped back into letters using the reverse of the mapping above. Given a string s containing only digits, return the number of ways to decode it.

There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n, return the number of possible unique paths that the robot can take to reach the bottom-right corner.

Given two strings text1 and text2, return the length of their longest common subsequence. If there is no common subsequence, return 0.

Given a string s, return the number of palindromic substrings in it. A string is a palindrome when it reads the same backward as forward.

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right, which minimizes the sum of all numbers along its path. You can only move either down or right at any point in time.

Given two strings word1 and word2, return the minimum number of operations required to convert word1 to word2. Operations: insert, delete, or replace a character.

Given a string s, return the longest palindromic substring in s.

Given strings s1, s2, and s3, determine if s3 is formed by interleaving s1 and s2 while preserving their relative order.

Given a circular integer array nums, return the maximum possible sum of a non-empty subarray. A circular array means the end connects to the beginning.

Find the maximum profit with at most two transactions. You may not engage in multiple transactions simultaneously (you must sell the stock before you buy again).

Given an input string (s) and a pattern (p), implement wildcard pattern matching with support for '?' and '*' where: '?' Matches any single character. '*' Matches any sequence of characters (including the empty sequence).

Given a triangle array, return the minimum path sum from top to bottom. For each step, you may move to an adjacent number of the row below. More formally, if you are on index i on the current row, you may move to either index i or index i + 1 on the next row.

Given an m x n integers matrix, return the length of the longest increasing path in matrix. From each cell, you can either move in four directions: left, right, up, or down. You may not move diagonally or move outside the boundary.

Given two strings s and t, return the number of distinct subsequences of s which equals t. A subsequence of a string is a new string formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters.

Given an input string s and a pattern p, implement regular expression matching with support for '.' and '*' where: '.' Matches any single character. '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial).

Given a string s, partition s such that every substring of the partition is a palindrome. Return the minimum cuts needed for a palindrome partitioning of s.

You are given k identical eggs and you have access to a building with n floors. Your goal is to determine the minimum number of moves needed to find the critical floor f where eggs start breaking.

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.

Given a reference of a node in a connected undirected graph. Return a deep copy (clone) of the graph.

There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course bi first if you want to take course ai. Return true if you can finish all courses. Otherwise, return false.

Given two words beginWord and endWord, and a dictionary wordList, return the number of words in the shortest transformation sequence from beginWord to endWord (changing one letter at a time).

You are given a network of n nodes, labeled from 1 to n. You are also given times, a list of travel times as directed edges times[i] = (ui, vi, wi), where ui is the source node, vi is the target node, and wi is the time it takes for a signal to travel from source to target. We send a signal from a given node k. Return the minimum time it takes for all the n nodes to receive the signal. If it is impossible for all the n nodes to receive the signal, return -1.

You are given a list of airline tickets where tickets[i] = [fromi, toi] represent the departure and the arrival airports of one flight. Reconstruct the itinerary in order and return it.

You are given an array of variable pairs equations and an array of real numbers values, where equations[i] = [Ai, Bi] and values[i] represent the equation Ai / Bi = values[i]. Each Ai or Bi is a string that represents a single variable. You are also given some queries, where queries[j] = [Cj, Dj] represents the jth query where you must find the answer for Cj / Dj = ?. Return the answers to all queries.

There are n cities. Some of them are connected, while some are not. If city a is connected directly with city b, and city b is connected directly with city c, then city a is connected indirectly with city c. A province is a group of directly or indirectly connected cities and no other cities outside of the group. Return the total number of provinces.

Given an integer array nums, find the subarray with the largest sum, and return its sum.

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 at that position. Return true if you can reach the last index, or false otherwise.

There are n gas stations along a circular route, where the amount of gas at the ith station is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey with an empty tank at one of the gas stations. Return the starting gas station's index if you can travel around the circuit once in the clockwise direction, otherwise return -1.

Find the maximum profit from buying and selling stock with unlimited transactions. You may hold at most one share at a time.

The median is the middle value in an ordered integer list. Implement the MedianFinder class.

Given a characters array tasks, representing the tasks a CPU needs to do, where each letter represents a different task. Tasks could be done in any order. Each task is done in one unit of time. For each unit of time, the CPU could complete either one task or just be idle. However, there is a non-negative integer n that represents the cooldown period between two same tasks (the same letter in the array), that is that there must be at least n units of time between any two same tasks.

Given an integer array nums and an integer k, return the kth largest element in the array. Note that it is the kth largest element in the sorted order, not the kth distinct element.

A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Given the locations and heights of all the buildings, return the skyline formed by these buildings collectively.

Given an array of meeting time intervals consisting of start and end times [[s1,e1],[s2,e2],...] (si < ei), determine if a person could attend all meetings.

Given an array of meeting time intervals consisting of start and end times [[s1,e1],[s2,e2],...] (si < ei), find the minimum number of conference rooms required.

Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input.

Given the head of a singly linked list, reverse the list, and return the reversed list.

Given head, the head of a linked list, determine if the linked list has a cycle in it. A cycle exists if there is some node that can be reached again by continuously following the next pointer.

You are given the heads of two sorted linked lists list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists.

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

You are given an array of k linked-lists lists, each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it.

Given two non-empty linked lists representing two non-negative integers stored in reverse order, add them and return the sum as a linked list.

A linked list of length n is given such that each node contains an additional random pointer, which could point to any node in the list, or null. Construct a deep copy of the list.

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

Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the nodes.

Given the heads of two singly linked-lists headA and headB, return the node at which the two lists intersect. If the two linked lists have no intersection at all, return null.

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

Given the head of a singly linked list, group all the nodes with odd indices together followed by the nodes with even indices, and return the reordered list. The first node is considered odd, and the second node is even, and so on.

Write an algorithm to determine if a number n is happy. A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.

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, return 0.

Given an integer x, return true if x is a palindrome, and false otherwise.

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

Given an m x n matrix, return all elements of the matrix in spiral order.

Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0s. You must do it in place.

You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.

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

You are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window.

Given two strings s and p, return an array of all the start indices of p's anagrams in s. You may return the answer in any order.

Given a string s containing just the characters "(", ")", "{", "}", "[" and "]", determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order.

Given an array of integers heights representing the histogram's bar height where the width of each bar is 1, return the area of the largest rectangle in the histogram.

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Given a circular integer array nums, return the next greater number for every element. Search circularly if needed. Return -1 if no greater element exists.

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

Given a roman numeral, convert it to an integer.

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

Given the root of a binary tree, invert the tree, and return its root.

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

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 otherwise.

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

Find the lowest common ancestor (LCA) of two nodes in a binary tree. The LCA is the lowest node that has both p and q as descendants.

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).

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

Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree, construct and return the binary tree.

Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work.

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. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum is the sum of the node's values in the path. Given the root of a binary tree, return the maximum path sum of any non-empty path.

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.

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

Given a binary tree, determine if it is height-balanced. A height-balanced binary tree is a binary tree in which the depth of the two subtrees of every node never differs by more than one.

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

Given the root of a binary tree and an integer targetSum, return true if the tree has a root-to-leaf path such that adding up all the values along the path equals targetSum.

Given the root of a binary tree and an integer targetSum, return all root-to-leaf paths where the sum of the node values in the path equals targetSum.

Given the root of a binary tree, flatten the tree into a "linked list": The "linked list" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null. The "linked list" should be in the same order as a pre-order traversal of the binary tree.

You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL.

Given a binary tree, find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

Given the root of a binary tree, return the sum of all left leaves. A leaf is a node with no children. A left leaf is a leaf that is the left child of another node.

A trie (prefix tree) is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. Implement the Trie class with insert, search, and startsWith methods.

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward.

Find all unique triplets in the array which gives the sum of zero.

Find two lines that together with the x-axis form a container, such that the container contains the most water.

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.

Write a function that reverses a string. The input string is given as an array of characters s. You must do this by modifying the input array in-place with O(1) extra memory.

Given an integer array nums sorted in non-decreasing order, remove the duplicates in-place such that each unique element appears only once. Return the number of unique elements.