Building Teams

#include <bits/stdc++.h>
using namespace std;

int main () {
    int n, m;
    cin >> n >> m;
    vector<vector<int>> fs(n+1);
    for(int i=0; i < m; i++) {
        int l, r; cin >> l >> r;
        fs[l].push_back(r);
        fs[r].push_back(l);
    }

    vector<int> c(n+1);
    stack<int> st;
    for(int i=1; i <= n; i++) {
        if(c[i]) continue;
        c[i] = 1;
        st.push(i);
        while(!st.empty()) {
            auto cd = st.top(); st.pop();
            for(int n : fs[cd]) {
                if (c[n] == c[cd]) {
                    cout << " IMPOSSIBLE\n";
                    return 0; 
                }
                c[n] = 3 ^ c[cd];
            }
        }
    }

    cout << c[1];
    for(int i = 2; i <= n; i++)
        cout << ' ' << c[i];
    cout << '\n';

    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: ACCEPTED

Test 5

Verdict: WRONG ANSWER

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER