Dos colors - P29033

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

vector< vector<int> > g;

//c=0 is one color, c=1 is another color

bool color(vector< vector<int> >&g, vector<int>& gc, int u, int c){
    if(gc[u]==NULL){
        gc[u]=c;
        for(int v : g[u]){
            if(!color(g,gc,v,1-c)) return false;
        }
        return true;
    }
    else return gc[u]==c;
}
bool complete_coloring(vector< vector<int> >&g, vector<int>& gc, int x){
    if(x == gc.size()-1) return true;
    else{
        if(gc[x]==NULL){
            return color(g,gc,x,0) && complete_coloring(g,gc,x+1);
        }
        else return complete_coloring(g,gc,x+1);
    }
}

int main(){
    int n,m;
    while(cin>>n){
        cin>>m;
        g = vector< vector<int> > (n);
        int x,y;
        for(int i=0; i<m; ++i){
            cin>>x>>y;
            g[x].push_back(y);
            g[y].push_back(x);
        }
        vector<int> gc(n);
        if(complete_coloring(g,gc,0)) cout<<"yes"<<endl;
        else cout<<"no"<<endl;
    }
}