743. 网络延迟时间 有 N 个网络节点,标记为 1 到 N. 给定一个列表 times,表示信号经过有向边的传递时间. times[i] = (u, v, w),其中 u 是源节点,v 是目标节点, w 是一个信号从源节点传递到目标节点的时间. 现在,我们从某个节点 K 发出一个信号.需要多久才能使所有节点都收到信号?如果不能使所有节点收到信号,返回 -1. 示例: 输入:times = [[2,1,1],[2,3,1],[3,4,1]], N = 4, K = 2 输出:2 注意: N 的…
Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers. Ensure that numbers within the set are sorted in ascending order. Example 1…
Given a string S, you are allowed to convert it to a palindrome by adding characters in front of it. Find and return the shortest palindrome you can find by performing this transformation. For example: Given "aacecaaa", return "aaacecaaa&qu…
Given a 2D board and a list of words from the dictionary, find all words in the board. Each word must be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same le…
Design a data structure that supports the following two operations: void addWord(word)bool search(word) search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.…
There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: [0,1] Given the total number of courses and a l…
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 assume all four edges of the grid are all surrounded by…
