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<uint8_t> v(n+1);
    vector<int> dj;

    stack<int> st;
    for(int i=1; i <= n; i++) {
        st.push(i);
        while(!st.empty()){
            auto c = st.top(); st.pop();
            if(v[c] == 0) {
                v[i] = 1;
                if(i == c) dj.push_back(c);
                for(int n : fs[c]) st.push(n);
            }
        }
    }
    // cycle?
    stack<pair<int, int>> stp;
    for(int i : dj) {
        stp.push({i, 2});
        while(!stp.empty()){
            auto[c, d] = stp.top(); stp.pop();
            // cout << c << " (" << d << "):";
            int cse = d % 2;
            int vcse = v[c] % 2;
            if(v[c] == 1) {
                v[c]=d;
                for(int n : fs[c]) {
                    // cout << ' ' << n;
                    stp.push({n, d+1});
                }
                // cout << '\n';
            }
            else if (cse==vcse && d-v[c] > 2) {
                cout << "IMPOSSIBLE\n";
                return 0; 
            }
        }
    }

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

    return 0;
}

Test 1

Verdict: RUNTIME ERROR

Test 2

Verdict: RUNTIME ERROR

Test 3

Verdict: RUNTIME ERROR

Test 4

Verdict: RUNTIME ERROR

Test 5

Verdict: RUNTIME ERROR

Test 6

Verdict: RUNTIME ERROR

Test 7

Verdict: TIME LIMIT EXCEEDED

Test 8

Verdict: TIME LIMIT EXCEEDED

Test 9

Verdict: RUNTIME ERROR

Test 10

Verdict: TIME LIMIT EXCEEDED

Test 11

Verdict: TIME LIMIT EXCEEDED

Test 12

Verdict: TIME LIMIT EXCEEDED