Building Teams

#include <bits/stdc++.h>

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

    long long n, m;
    std::cin >> n >> m;

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

    std::vector team(n+1, 0);
    for (int i = 1; i <= n; i++) {
        if (team[i]) {
            continue;
        }
        team[i]=1;

        std::stack<int> stack;
        stack.push(i);
        while (!stack.empty()) {
            const int v = stack.top();
            stack.pop();
            for (int w : graph[v]) {
                if (team[w] == 0) {
                    if (team[v] == 1) {
                        team[w] = 2;
                    } else {
                        team[w] = 1;
                    }
                    stack.push(w);
                }
                else if (team[w] == team[v]) {
                    std::cout << "IMPOSSIBLE" << std::endl;
                    return 0;
                }
            }
        }
    }

    for (int i = 1; i <= n; i++) {
        std::cout << team[i] << ' ';
    }
    std::cout << std::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