Building Teams

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

const int MAXN=200000+30;

int main() {
    vector<int> adj[MAXN];
    bool visited[MAXN] = {false};
    int team[MAXN] = {0};

    int n, m;
    cin >> n >> m;

    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 (visited[i]) continue;

        team[i] = 1;
        queue<int> q;
        q.push(i);

        while (!q.empty()) {
            int node = q.front(); q.pop();
            visited[node] = true;
            for (int u: adj[node]) {
                if (team[node] == team[u]) {
                    cout << "IMPOSSIBLE" << endl;
                    return 0;
                } else {
                    team[u] = (team[node] == 1 ? 2 : 1);
                }
                if (!visited[u]) {
                    q.push(u);
                }
            }
        }
    }

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