Building Teams

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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, m;
    cin >> n >> m;
    vector<vector<int>> g(n + 1);
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        g[a].push_back(b);
        g[b].push_back(a);
    }

    vector<int> color(n + 1, 0);
    for (int i = 1; i <= n; i++) {
        if (color[i]) continue;
        queue<int> q;
        q.push(i);
        color[i] = 1;
        while (!q.empty()) {
            int u = q.front(); q.pop();
            for (int v : g[u]) {
                if (!color[v]) {
                    color[v] = 3 - color[u];
                    q.push(v);
                } else if (color[v] == color[u]) {
                    cout << "IMPOSSIBLE\n";
                    return 0;
                }
            }
        }
    }

    for (int i = 1; i <= n; i++) cout << color[i] << " ";
    cout << "\n";
}

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