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

Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

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

Given an integer array nums and an integer k, return the k most frequent elements.

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].

Determine if a 9x9 Sudoku board is valid.

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 integer array nums, rotate the array to the right by k steps, where k is non-negative. Do it in-place with O(1) extra space.

Given an integer numRows, return the first numRows of Pascal's triangle. In Pascal's triangle, each number is the sum of the two numbers directly above it.

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 a large integer represented as an integer array digits, increment the large integer by one and return the resulting array of digits.

Given an array nums of n integers where nums[i] is in the range [1, n], return an array of all the integers in the range [1, n] that do not appear in nums. You must write an algorithm that runs in O(n) time and uses only constant extra space.

Given a list of non-negative integers nums, arrange them such that they form the largest number and return it.

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

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.

A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros. Given a string s containing only digits, return all possible valid IP addresses that can be formed by inserting dots into s.

Place n queens on an n x n chessboard such that no two queens attack each other. Return all distinct solutions.

Given two integers n and k, return all possible combinations of k numbers chosen from the range [1, n]. You may return the answer in any order.

Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row, column, and 3x3 sub-box.

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.

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 two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)).

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

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

Given a non-empty array of integers nums, every element appears twice except for one. Find that single one. You must implement a solution with linear runtime complexity and use only constant extra space.

Reverse bits of a given 32-bit unsigned integer.

Write a function that takes the binary representation of an unsigned integer and returns the number of 1 bits it has (also known as the Hamming weight).

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

Given an integer n, return an array ans of length n + 1 such that for each i (0 <= i <= n), ans[i] is the number of 1's in the binary representation of i.

Given two integers a and b, return the sum of the two integers without using the operators + and -. Use bitwise operations instead.

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.

Design and implement a data structure for a Least Frequently Used (LFU) cache. Implement get and put operations with O(1) time complexity.

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.

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.

You are given an integer array cost where cost[i] is the cost of ith step on a staircase. Once you pay the cost, you can either climb one or two steps. You can either start from the step with index 0, or the step with index 1. Return the minimum cost to reach the top of the floor.

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 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.

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.

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 a string s, find the longest palindromic subsequence's length in s. A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements.

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).

We have n jobs, where every job is scheduled to be done from startTime[i] to endTime[i], obtaining a profit of profit[i]. Return the maximum profit you can take such that there are no two jobs with overlapping time ranges.

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.

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.

Return a list of grid coordinates where water can flow to both the Pacific and Atlantic oceans.

There are n cities connected by some number of flights. You are given an array flights where flights[i] = [fromi, toi, pricei] indicates that there is a flight from city fromi to city toi with cost pricei. You are also given three integers src, dst, and k, return the cheapest price from src to dst with at most k stops. If there is no such route, return -1.

You are given an m x n grid where each cell can have one of three values: 0 (empty), 1 (fresh orange), or 2 (rotten orange). Every minute, any fresh orange that is 4-directionally adjacent to a rotten orange becomes rotten. Return the minimum number of minutes until no cell has a fresh orange. If impossible, return -1.

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 the ordering of courses you should take to finish all courses. If there are many valid answers, return any of them. If it is impossible to finish all courses, return an empty array.

Given a list of accounts where each account contains a name and emails, merge accounts belonging to the same person (accounts that share at least one common email).

You are given an array points representing integer coordinates of some points on a 2D-plane, where points[i] = [xi, yi]. The cost of connecting two points [xi, yi] and [xj, yj] is the manhattan distance between them: |xi - xj| + |yi - yj|. Return the minimum cost to make all points connected.

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.

You are a hiker preparing for an upcoming hike. You are given heights, a 2D array of size rows x columns, where heights[row][col] represents the height of cell (row, col). You are situated in the top-left cell, (0, 0), and you hope to travel to the bottom-right cell, (rows-1, columns-1). The effort required to travel from one cell to an adjacent cell is the absolute difference of their heights. Return the minimum effort required to travel from the top-left cell to the bottom-right cell.

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.

You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. Return the minimum number of jumps to reach nums[n - 1].

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

There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings. You are giving candies to these children subjected to the following requirements: Each child must have at least one candy. Children with a higher rating get more candies than their neighbors. Return the minimum number of candies you need to have to distribute the candies to the children.

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

Given a string s, rearrange the characters of s so that any two adjacent characters are not the same. Return any possible rearrangement of s or return "" if not possible.

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.

Design a class to find the kth largest element in a stream. Note that it is the kth largest element in the sorted order, not the kth distinct element.

Given an array of points where points[i] = [xi, yi] represents a point on the X-Y plane and an integer k, return the k closest points to the origin (0, 0). The distance between two points is the Euclidean distance. You may return the answer in any order.

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.

Design a simplified version of Twitter where users can post tweets, follow/unfollow another user, and see the 10 most recent tweets in their news feed. Implement the Twitter class with postTweet, getNewsFeed, follow, and unfollow methods.

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.

You are given an array of non-overlapping intervals intervals where intervals[i] = [starti, endi] represent the start and the end of the ith interval and intervals is sorted in ascending order by starti. You are also given an interval newInterval = [start, end] that represents the start and end of another interval. Insert newInterval into intervals such that intervals is still sorted in ascending order by starti and intervals still does not have any overlapping intervals (merge overlapping intervals if necessary).

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 head of a singly linked-list. The list can be represented as: L0 → L1 → … → Ln - 1 → Ln. Reorder the list to be on the following form: L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → …

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.

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 singly linked list, return true if it is a palindrome or false otherwise.

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 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.

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

Given the head of a singly linked list, return the middle node of the linked list. If there are two middle nodes, return the second middle node.

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.

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

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.

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string. You must not use any built-in BigInteger library or convert the inputs to integer directly.

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 a positive integer n, generate an n x n matrix filled with elements from 1 to n² in spiral order.

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 a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times. Return the length of the longest substring containing the same letter you can get after performing the above operations.

Given an array of positive integers nums and a positive integer target, return the minimal length of a subarray whose sum is greater than or equal to target. If there is no such subarray, return 0.

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.

Evaluate the value of an arithmetic expression in Reverse Polish Notation. Valid operators are +, -, *, and /. Each operand may be an integer or another expression. Note that division between two integers should truncate toward zero.

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

Given an encoded string, return its decoded string. The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is being repeated exactly k times.

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 a string s consisting of words and spaces, return the length of the last word in the string.

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.

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).

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, 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 all root-to-leaf paths in any order.

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.

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

Two nodes of a BST are swapped by mistake. Recover the tree without changing its structure.

Given an array of strings words (without duplicates), return all the concatenated words in the given list. A concatenated word is a string that is comprised entirely of at least two shorter words in the given array.

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 two numbers that add up to a specific target number in a sorted array. Return 1-based indices.

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.

Given an array with n objects colored red, white, or blue (represented by 0, 1, and 2), sort them in-place so that objects of the same color are adjacent (Dutch National Flag problem).

Given an integer array nums sorted in non-decreasing order, return an array of the squares of each number sorted in non-decreasing order.