[Swift]LeetCode261.图验证树 $ Graph Valid Tree

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.

For example:

Given n = 5 and edges = [[0, 1], [0, 2], [0, 3], [1, 4]], return true.

Given n = 5 and edges = [[0, 1], [1, 2], [2, 3], [1, 3], [1, 4]], return false.

Hint:

  1. Given n = 5 and edges = [[0, 1], [1, 2], [3, 4]], what should your return? Is this case a valid tree?
  2. According to the definition of tree on Wikipedia: “a tree is an undirected graph in which any two vertices are connected by exactly one path. In other words, any connected graph without simple cycles is a tree.”

Note: you can assume that no duplicate edges will appear in edges. Since all edges are undirected, [0, 1] is the same as [1, 0] and thus will not appear together in edges.



给定n个标记为0到n-1的节点和一个无向边列表(每个边都是一对节点),编写一个函数来检查这些边是否构成有效的树。

例如:

如果n=5且边数为[[0,1],[0,2],[0,3],[1,4]],则返回true。

如果n=5且边数为[[0,1],[1,2],[2,3],[1,3],[1,4]],则返回false。

提示:

考虑到n=5和edges=[[0,1],[1,2],[3,4]],你应该返回什么?这是一个有效的树吗?

根据维基百科上树的定义:“树是一个无向图,其中任何两个顶点都由一条路径连接。换句话说,任何没有简单循环的连通图都是一棵树。”

注意:可以假定边中不会出现重复的边。因为所有边都是无向的,[0,1]与[1,0]相同,因此不会在边中一起出现。



BFS

 1 class Solution {
 2     func validTree(_ n:Int,_ edges:[[Int]]) -> Bool{
 3         var g:[Set<Int>] = [Set<Int>](repeating:Set<Int>(),count:n)
 4         var s:Set<Int> = [0]
 5         var q:[Int] = [0]
 6         for a in edges
 7         {
 8             g[a[0]].insert(a[1]);
 9             g[a[1]].insert(a[0]);
10         }
11         while(!q.isEmpty)
12         {
13             var t:Int = q.first!
14             q.removeFirst()
15             for a in g[t]
16             {
17                 if s.contains(a)
18                 {
19                     return false
20                 }
21                 s.insert(a)
22                 q.append(a)
23                 g[a].remove(t)
24             }
25         }
26          return s.count == n
27     }
28 }

原文地址:https://www.cnblogs.com/strengthen/p/10227256.html

时间: 01-06

[Swift]LeetCode261.图验证树 $ Graph Valid Tree的相关文章

Leetcode: Graph Valid Tree &amp;&amp; Summary: Detect cycle in directed graph and undirected graph

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. For example: Given n = 5 and edges = [[0, 1], [0, 2], [0, 3], [1, 4]], return tru

[LeetCode#261] Graph Valid Tree

Problem: 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. For example: Given n = 5 and edges = [[0, 1], [0, 2], [0, 3], [1, 4]], r

Graph Valid Tree

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. Notice You can assume that no duplicate edges will appear in edges. Since all edg

[LintCode] Graph Valid Tree

http://www.lintcode.com/en/problem/graph-valid-tree/ DFS 解法: public class Solution { /** * @param n an integer * @param edges a list of undirected edges * @return true if it's a valid tree, or false */ public boolean validTree(int n, int[][] edges) {

LeetCode Graph Valid Tree

原题链接在这里:https://leetcode.com/problems/graph-valid-tree/ 题目: 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. For example: Given n

Graph Valid Tree -- LeetCode

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. For example: Given n = 5 and edges = [[0, 1], [0, 2], [0, 3], [1, 4]], return tru

261. Graph Valid Tree

也是卡了好多天的题目 主要就是介绍了union-find的算法,用于检查Undirected graph有没有环 http://www.geeksforgeeks.org/union-find/ 1 public boolean validTree(int n, int[][] edges) { 2 int[] parent = new int[n]; 3 Arrays.fill(parent, -1); 4 for(int i = 0; i < edges.length ; i++) { 5

对照层关系图验证代码

  包括要在验证期间分析的特定程序集或项目在 “解决方案资源管理器”中,右击建模项目或 “层引用”文件夹,然后单击 “添加引用”.    在 “添加引用”对话框中,选择所需程序集或项目,然后单击 “确定”.    随时手动验证代码从打开的层关系图中验证代码 右击关系图图面,再单击 “验证体系结构”.     说明  默认情况下,层关系图 (.layerdiagram) 文件的 “生成操作”属性设置为 “验证”,以便在验证过程中包括关系图.       “错误列表”窗口会报告发生的任何错误. 有关

leetcode 261-Graph Valid Tree(medium)(BFS, DFS, Union find)

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. 这道题主要就是判断1.是否有环路 2. 是否是连通图 可以用DFS, BFS 和 Union find,union find最合适. 对于DFS和BFS,首先都是建立