Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors. OJ's undirected graph serialization: Nodes are labeled uniquely. We use # as a separator for each node, and , as a separator for node label and each neigh…

Given a binary tree, find the leftmost value in the last row of the tree. Example 1: Input: 2 / \ 1 3 Output: 1 Example 2: Input: 1 / \ 2 3 / / \ 4 5 6 / 7 Output: 7 Note: You may assume the tree (i.e., the given root node) is not NULL. 这个题的思路其实跟[Lee…

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between). For example:Given binary tree [3,9,20,null,null,15,7], 3 / \ 9 20 / \ 15 7 retur…

There is a ball in a maze with empty spaces and walls. The ball can go through empty spaces by rolling up, down, left or right, but it won't stop rolling until hitting a wall. When the ball stops, it could choose the next direction. Given the ball's …

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 lis…

Given n nodes labeled from 0 to n-1 and a list of undirected edges (each edge is a pair of nodes), write a function to check whether these edges make up a valid tree. Example 1: Input: n = 5, and edges = [[0,1], [0,2], [0,3], [1,4]] Output: true Exam…

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…

Given 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. Example: Input: [1,2,3,null,5,null,4] Output: [1, 3, 4] Explanation: 1 <--- / \ 2 3 <--- \ \ 5 4 <--- 这…

We are given a binary tree (with root node root), a target node, and an integer value `K`. Return a list of the values of all nodes that have a distance K from the target node.  The answer can be returned in any order. Example 1: Input: root = [3,5,1…

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors. OJ's undirected graph serialization: Nodes are labeled uniquely. We use # as a separator for each node, and , as a separator for node label and each neigh…

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors. OJ's undirected graph serialization: Nodes are labeled uniquely. We use # as a separator for each node, and , as a separator for node label and each neigh…

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors. OJ's undirected graph serialization: Nodes are labeled uniquely.We use # as a separator for each node, and , as a separator for node label and each neighb…

原题地址 方法I,DFS 一边遍历一边复制 借助辅助map保存已经复制好了的节点 对于原图中每个节点,如果已经复制过了,直接返回新节点的地址,如果没复制过,则复制并加入map中,接着依次递归复制其兄弟. 代码: map<UndirectedGraphNode *, UndirectedGraphNode *> old2new; UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) { if (!node) return NULL;…

Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine if s can be segmented into a space-separated sequence of one or more dictionary words. Note: The same word in the dictionary may be reused multiple t…

题目 给定一个无向图的节点,克隆能克隆的一切 思路 1--2 | 3--5 以上图为例, node    neighbor 1         2, 3 2         1 3         1, 5 5         3 首先从1开始,  将(node,newNode)put到HashMap中 node        newNode 1                1 然后遍历该node的所有neighbor node    neighbor 1         2, 3 此时遍历到…

Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord, such that: Only one letter can be changed at a time. Each transformed word must exist in the word li…

题目描述: 给定一个由 '1'(陆地)和 '0'(水)组成的的二维网格,计算岛屿的数量.一个岛被水包围,并且它是通过水平方向或垂直方向上相邻的陆地连接而成的.你可以假设网格的四个边均被水包围. 示例 1: 输入: 11110 11010 11000 00000 输出: 1 示例 2: 输入: 11000 11000 00100 00011 输出: 3 思路分析:题解和示例图来自:liweiwei1419 说明:以下介绍的算法,除了并查集以外,DFS 和 BFS 都属于很基础的算法内容,也非常好理…

Given an array of non-negative integers, you are initially positioned at the first index of the array. Each element in the array represents your maximum jump length at that position. Determine if you are able to reach the last index. Example 1: Input…

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree [1,2,2,3,4,4,3] is symmetric: 1 / \ 2 2 / \ / \ 3 4 4 3 But the following [1,2,2,null,3,null,3] is not: 1 / \ 2 2 \ \ 3 3 Not…

For a undirected graph with tree characteristics, we can choose any node as the root. The result graph is then a rooted tree. Among all possible rooted trees, those with minimum height are called minimum height trees (MHTs). Given such a graph, write…

You are given a m x n 2D grid initialized with these three possible values. -1 - A wall or an obstacle. 0 - A gate. INF - Infinity means an empty room. We use the value 231 - 1 = 2147483647 to represent INF as you may assume that the distance to a ga…

A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below). The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in t…

Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results. Note: The input string may contain letters other than the parentheses ( and ). Example 1: Input: "()())()" Output: ["()()…

A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below). The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in t…

In a row of seats, 1 represents a person sitting in that seat, and 0 represents that the seat is empty. There is at least one empty seat, and at least one person sitting. Alex wants to sit in the seat such that the distance between him and the closes…

Given a string S and a character C, return an array of integers representing the shortest distance from the character C in the string. Example 1: Input: S = "loveleetcode", C = 'e' Output: [3, 2, 1, 0, 1, 0, 0, 1, 2, 2, 1, 0] Note: S string leng…

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. Note: You can only move either down or right at any point in time. Example: Input: [   [1,3,1], [1,5…

BFS/DFS 在树专题和回溯算法中其实已经涉及到了BFS和DFS算法,这里单独提出再进一步学习一下 BFS 广度优先遍历 Breadth-First-Search 这部分的内容也主要是学习了labuladong公众号内的相关讲解 算法流程 首先将开始节点放入队列中. 从队列中取出第一个节点,并检验它是否为目标. 如果找到目标,则结束搜索并回传结果. 否则将它所有尚未检验过的直接子节点加入队列中. 若队列为空,表示整张图都检查过了--亦即图中没有欲搜索的目标.结束搜索并回传"找不到目标"…

Cleaning Robot (bfs+dfs) Here, we want to solve path planning for a mobile robot cleaning a rectangular room floor with furniture. Consider the room floor paved with square tiles whose size fits the cleaning robot (1 * 1). There are 'clean tiles' and…

133. Clone Graph Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors. OJ's undirected graph serialization: Nodes are labeled uniquely. We use # as a separator for each node, and , as a separator for node lab…