Building Teams

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

vector<int> A[200'001];
int Z[200'001];

void f(int i, int z) {
	if (Z[i]) {
		if (Z[i] != z) {
			cout << "IMPOSSIBLE";
			exit(0);
		}
		return;
	}
	Z[i] = z;
	z = z == 1 ? 2 : 1;
	for (int j : A[i]) {
		f(j,z);
	}
}

int main() {
	int n, m;
	cin >> n >> m;
	for (int i = 0; i < m; ++i) {
		int a, b;
		cin >> a >> b;
		A[a].push_back(b);
		A[b].push_back(a);
	}
	for (int i = 0; i < n; ++i) {
		if (!Z[i]) f(i, 1);
	}
	for (int i = 0; i < n; ++i) {
		cout << (Z[i] ? "1 " : "2 ");
	}
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED