Building Teams

#include <cstdio>
#include <iostream>
#include <queue>
#include <utility>
#include <vector>

using namespace std;

// Depth first search
void dfs(int s, bool visited[], vector<int> adj[]) {
    if (visited[s]) {
        return;
    };
    visited[s] = true;
    for (auto u: adj[s]) {
        dfs(u, visited, adj);
    }
}

int main (int argc, char *argv[]) {
    int n, m;
    cin >> n >> m;
    vector<pair<int, int>> friends(m);
    for (int i = 0; i < m; i++) {
        cin >> friends[i].first >> friends[i].second;
    }
    // 0 is not included in cities
    vector<int> adj[n + 1];
    bool visited[n + 1];
    /*bool color[n + 1];*/
    for (int i = 0; i < n + 1; i++) {
        visited[i] = false;
        /*color[i] = false;*/
    }

    // Add roads to adjacent structure
    for (int j = 0; j < m; j++) {
        adj[friends[j].first].push_back(friends[j].second);
        adj[friends[j].second].push_back(friends[j].first);
    }

    queue<int> q;
    int distance[n + 1];

    distance[1] = 0;
    q.push(1);

    int k = 1;
    vector<int> color(n+1, 0);
    while (!visited[k]) {
        visited[k] = true;
        color[k] = 0;
        while (!q.empty()) {
            int s = q.front(); q.pop();
            /*cout << s << " " << color[s] << "\n";*/

            for (int u: adj[s]) {
                if (visited[u] && color[s] == color[u]) {
                    cout << "IMPOSSIBLE";
                    return 0;
                } else if (visited[u]) continue;
                /*cout << u;*/
                visited[u] = true;
                distance[u] = distance[s]+1;
                color[u] = (1 - color[s]);
                q.push(u);
            }
        }

        // find next unconnected component
        for (int i = k; i < n + 1; i++) {
            if (!visited[i]) {
                k = i;
                q.push(i);
                break;
            }
        }
    }

    for (int i = 1; i < n + 1; i++) {
        if (distance[i] % 2) {
            cout << "1 ";
        } else {
            cout << "2 ";
        }
    }
    cout << "\n";

    /*for (int a = 0; a < n + 1; a++) {*/
    /*    cout << a << ": " << visited[a] << "\n";*/
    /*}*/

    /*std::cout << added << "\n";*/
    /*for (auto u: added_edges) {*/
    /*    cout << u - 1 << " " << u << "\n";*/
    /*}*/
    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