There is an m x n rectangular island that borders both the Pacific Ocean and Atlantic Ocean. The Pacific Ocean touches the island’s left and top edges, and the Atlantic Ocean touches the island’s righ

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 diagonall

Given a string s and an integer k, return the number of substrings in s of length k with no repeated characters. Example 1:Input: s = “havefunonleetcode”, k = 5Output: 6Explanation: There ar

There is an undirected graph with n nodes, where each node is numbered between 0 and n - 1. You are given a 2D array graph, where graph[u] is an array of nodes that node u is adjacent to. More formall

Given an array of integers nums, return the number of good pairs. A pair (i, j) is called good if nums[i] == nums[j] and i < j. Example 1:Input: nums = [1,2,3,1,1,3]Output: 4Explanat

You are given a doubly linked list, which contains nodes that have a next pointer, a previous pointer, and an additional child pointer. This child pointer may or may not point to a separate doubly lin

You are given a string s. We want to partition the string into as many parts as possible so that each letter appears in at most one part. Note that the partition is done so that after concatenating al

We have a wooden plank of the length n units. Some ants are walking on the plank, each ant moves with speed 1 unit per second. Some of the ants move to the left, the other move to the right. When two

Design an algorithm to encode a list of strings to a string. The encoded string is then sent over the network and is decoded back to the original list of strings. Machine 1 (sender) has the function:

The count-and-say sequence is a sequence of digit strings defined by the recursive formula:countAndSay(1) = “1”countAndSay(n) is the way you would “say” the digit string from countAndSay(n-1), wh