Building Teams

#include <bits/stdc++.h>

using namespace std;

bool dfs(int x, int tag, vector<int> &seen, vector<vector<int>> &adj) {

    for (int y : adj[x]) {
        if (seen[y] == -1) {
            seen[y] = (tag+1)%2;
            bool z = dfs(y, (tag+1)%2, seen, adj);
            if (!z)
                return false;
        } else if (seen[y] == tag)
            return false;
    }

    return true;

}

int main() {

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

    vector<int> seen(n);
    vector<vector<int>> adj(n);

    for (int i = 0; i < n; i++) {
        seen[i] = -1;
        adj[i] = {};
    }

    for (int j = 0; j < m; j++) {
        int a, b;
        cin >> a >> b;
        adj[a-1].push_back(b-1);
        adj[b-1].push_back(a-1);
    }

    for (int k = 0; k < n; k++) {
        if (seen[k] == -1) {
            seen[k] = 0;
            bool r = dfs(k, 0, seen, adj);
            if (!r) {
                cout << "IMPOSSIBLE" << endl;
                return 0;
            }
        }
    }
    
    for (int i = 0; i < n; i++)
        cout << seen[i]+1 << " ";
    cout << endl;

    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