Building Teams

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

typedef long long ll;

int get_new_pupil(int *g, int size) {
  static int i = 1;
  for (; i < size; i++) {
    if (g[i] == -1)
      return i;
  }
  return -1;
}

void bfs() {

}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);

  ll n, m;
  cin >> n >> m;
  vector<ll> f[n + 1];
  int g[n + 1];
  memset(g, -1, (n + 1) * sizeof(int));
  int a, b;
  for (int i = 0; i < m; i++) {
    cin >> a >> b;
    f[a].push_back(b);
    f[b].push_back(a);
  }

  int curr_p;
  pair<ll, int> q_top;
  queue<pair<ll, int>> q;
  while ((curr_p = get_new_pupil(g, n + 1)) != -1) {
    q.push(make_pair(curr_p, 1));
    while (q.size() > 0) {
      q_top = q.front();
      q.pop();
      // cout << q_top.first << endl;
      if (g[q_top.first] != -1 && g[q_top.first] != q_top.second) {
        cout << "IMPOSSIBLE" << "\n";
        return 0;
      }
      // cout << g[q_top.first] << endl;

      g[q_top.first] = q_top.second;
      for (auto ff : f[q_top.first]) {
        // cout << "(" << ff << " " << g[ff] << ")";
        if (g[ff] == -1) {
          g[ff] = (q_top.second + 1) % 2;
          q.push(make_pair(ff, (q_top.second + 1) % 2));
        }
        else if (g[ff] != (q_top.second + 1) % 2) {
          cout << "IMPOSSIBLE" << "\n";
          return 0;
        }
      }
    }
  }

  for (int i = 1; i < n+1; i++) {
    if (i != 1)
      cout << " ";
    cout << g[i]+ 1;
  }
  cout << "\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