Building Teams

#include <iostream>
#include <vector>
#include <queue>

using namespace std;

int main() {
    int n, m;
    if (!(cin >> n >> m)) return 0;

    vector<vector<int>> adj(n + 1);
    for (int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    vector<int> team(n + 1, 0);

    for (int i = 1; i <= n; i++) {
        if (team[i] != 0) continue;
        queue<int> q;
        q.push(i);
        team[i] = 1; 

        while (!q.empty()) {
            int u = q.front();
            q.pop();

            for (int v : adj[u]) {
                if (team[v] == 0) {
                    team[v] = 3 - team[u]; 
                    q.push(v);
                } else if (team[v] == team[u]) {
                    cout << "IMPOSSIBLE\n";
                    return 0;
                }
            }
        }
    }

    for (int i = 1; i <= n; i++) {
        cout << team[i] << (i == n ? "" : " ");
    }
    cout << "\n";

    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