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() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(NULL);

    int 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::queue<int> q;
 
    std::vector<int> team(n + 1, 0);
 
    for (int i = 1; i <= n; ++i) {
        if (!team[i]) {
            q.push(i);
            team[i] = 1;
            // 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 (team[u] == team[s]) {
                        // std::cout << "u: " << u << std::endl;
                        std::cout << "IMPOSSIBLE";
                        return (0);
                    }
                    if (team[u] == 0) {
                        team[u] = 3 - team[s];
                        q.push(u);
                    }
                    // std::cout << "team: " << res[s] + 1 << std::endl;
                }
            }
        }
    }
 
    for (int i = 1; i <= n; ++i) {
        std::cout << team[i] << " ";
    }
    std::cout << "\n";
}

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