Bosc - X41530

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

typedef vector<int> Vec;
typedef vector<Vec> Matrix;

Matrix graph;

bool cycle(vector< vector<int> >& g, int parent, int  u, vector<bool>& visited){
        if(visited[u]) return true;
        else{
            visited[u]=true;
            for(int v : g[u]){
                if (v != parent and  cycle(g, u, v, visited)) return true;
            }
        }
        return false;
}

int main(){
    int n,m;
    while(cin>>n){
        cin>>m;
        graph = Matrix(n);

        int x,y;
        for(int i=0; i<m; ++i){
            cin>>x>>y;
            graph[x].push_back(y);
            graph[y].push_back(x);
        }
        int trees=0;
        bool has_cycle=false;

        vector<bool> visited(n,false);
        for(int i=0; i<n; ++i){
            if(!visited[i]){
                if(!cycle(graph,-1,i,visited)) ++trees;
                else has_cycle = true;
            }
        }
        if(has_cycle) cout<<"no"<<endl;
        else cout<<trees<<endl;
    }
}