Building Teams

#include <bits/stdc++.h>

void dfs(int s, std::vector<bool>& visited, std::vector<std::vector<int>>& graph) {
    if (visited[s]) return ;
    visited[s] = true;
    for (auto u : graph[s])
        dfs(u, visited, graph);
}

int main() {
    int n, m;
    std::cin >> n >> m;

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

    std::queue<int> q;

    std::vector<bool> visited(n + 1, false);
    std::vector<int> res(n + 1, -1);


    std::vector<int> r={};

    int team = 0;
    for (int i = 1; i <= n; ++i) {
        if (!visited[i]) {
            visited[i] = true;
            q.push(i);
            res[i] = team;
            // std::cout << "res[" << i << "] team: " << res[i] << std::endl;

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

                for (auto u : graph[s]) {
                    // std::cout << "parent: " << s << " child: " << u << std::endl;
                    if (res[u] != (res[s] + 1) % 2 && res[u] != -1) {
                        // std::cout << "u: " << u << std::endl;
                        std::cout << "IMPOSSIBLE";
                        return (0);
                    }
                    if (visited[u]) continue;
                    visited[u] = true;
                    // std::cout << "team: " << res[s] + 1 << std::endl;
                    
                    res[u] = (res[s] + 1) % 2;
                    q.push(u);
                }
            }
        }
    }

    for (size_t i = 1; i + 1 < res.size() + 1; ++i) {
        std::cout << res[i] + 1 << " ";
    }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: ACCEPTED

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