Building Teams

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

vector< vector<int> > adj;
vector<int> team;

int dfs(int pupil, int currentTeam){
	team[pupil] = currentTeam;
	for(int i : adj[pupil]){
		if(team[i] == 0){
			if(!dfs(i, 3 - currentTeam)) return false;
		}
		else if(team[i] == currentTeam) return false;
	}
	return true;
}


int main(){
	
	int n, m;
	cin >> n >> m;
	
	adj.resize(n + 1);
	team.assign(n + 1, 0);
	
	for(int i = 0; i < m; i++){
		int a, b;
		cin >> a >> b;
		adj[a].push_back(b);
		adj[b].push_back(a);
	}
	
	for(int i = 1; i <= n; i++){
		if(team[i] == 0){
			if(!dfs(i, 1)){
				cout << "IMPOSSIBLE" << endl;
				return 0;
			}
		}
	}
	for(int i = 1; i <= n; i++){
		cout<<team[i]<<" ";
	}
	cout << endl;
	
	return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED