X41530 - Forest

#include <iostream>
#include <vector>
#include <queue>
using namespace std;

void dfs(const vector<vector<int> >& g, vector<bool>& visited, int u, bool& forest, int ant, int antant){
    if(!visited[u]){
        visited[u] = true;
        for(int i = 0; i < g[u].size(); ++i){
            dfs(g,visited,g[u][i], forest, u, ant);
        }
    }
    else if(visited[u] && u != antant){
        forest = false;
    }
}

void dfs_1(const vector<vector<int> >& g, vector<bool>& visited, int& count,bool& forest){
    for(int i = 0; i < g.size(); ++i){
        if(!visited[i]){
            ++count;
            dfs(g,visited,i,forest, i, -1);
        }
    }
}

int main(){
    int n,m;
    while(cin >> n >> m){
        vector<vector<int> > g(n);
        for(int i = 0; i < m; ++i){
            int x,y;
            cin >> x >> y;
            g[x].push_back(y);
            g[y].push_back(x);
        }
        vector<bool> visited(n,false);
        bool forest = true;
        int count = 0;
        dfs_1(g,visited,count,forest);
        if (!forest) cout << "no" << endl;
        else cout << count << endl;
    }
}