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

创建一个基于时间的键值存储类 TimeMap，它支持下面两个操作： set(string key, string value, int timestamp) 存储键 key、值 value，以及给定的时间戳 timestamp。 get(string key, int timestamp) 返回先前调…

Given an array of numbers nums, in which exactly two elements appear only once and all the other elements appear exactly twice. Find the two elements that appear only once.

Given a non-empty array of integers, every element appears three times except for one, which appears exactly once. Find that single one.

Implement a trie with insert, search, and startsWith methods.

All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T, for example: “ACGAATTCCG”. When studying DNA, it is sometimes useful to identify repeated sequences within the DNA.

Given an array of n positive integers and a positive integer s, find the minimal length of a contiguous subarray of which the sum ≥ s. If there isn’t one, return 0 instead.

Given a 2d grid map of ‘1’s (land) and ‘0’s (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may ass…

Given a range [m, n] where 0 <= m <= n <= 2147483647, return the bitwise AND of all numbers in this range, inclusive.

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.