261. Graph Valid Tree

Posted 2020-10-15 jxr041100

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.

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.

 

class Solution {
public:
    bool validTree(int n, vector<pair<int, int>>& edges) {
        vector<int>roots(n,-1);
        for(auto edge:edges)
        {
            int x = findroots(roots,edge.first),y = findroots(roots,edge.second);
            if(x==y) return false;
            roots[x] = y;
        }
        return edges.size()==n-1;
    }
private:
    int findroots(vector<int> &roots,int x)
    {
        while(roots[x]!=-1) x = roots[x];
        return x;
    }
};