[Leetcode] Graph Valid Tree

Problem Description:

Given n nodes labeled from 0 n - 1 to and a list of undirected edges (each edge is a pair of nodes), write a funct Ion to check whether these edges make up a valid tree.

For example:

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

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

Hint:

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

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

As suggested by the hint, just check for cycle and connectedness in the graph. Both of these can be done via DFS.

The code is as follows.

1 classSolution {2  Public:3     BOOLValidtree (intN, vector<pair<int,int>>&edges) {4vector<vector<int>>Neighbors (n);5          for(Auto e:edges) {6 Neighbors[e.first].push_back (e.second);7 Neighbors[e.second].push_back (e.first);8         }9vector<BOOL> Onpath (N,false), visited (N,false);Ten         if(Hascycle (Neighbors,0, -1, Onpath, visited)) One             return false; A          for(BOOLv:visited) -             if(!V)return false;  -         return true; the     } - Private: -     BOOLHascycle (vector<vector<int>>& Neighbors,intKidintParent, vector<BOOL>& Onpath, vector<BOOL>&visited) { -         if(Onpath[kid])return true; +Onpath[kid] = Visited[kid] =true; -          for(Auto Neigh:neighbors[kid]) +             if(neigh! = parent &&hascycle (Neighbors, neigh, Kid, Onpath, visited)) A                 return true; at         returnOnpath[kid] =false; -     } -};

[Leetcode] Graph Valid Tree