Tunnelit

input/code.cpp: In function 'int main()':
input/code.cpp:25:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int qi = 0; qi < q.size(); ) {
                                ^

#include <iostream>
#include <vector>
#define F first
#define S second
using namespace std;
int from[101010], to[101010];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  vector<pair<int, int>> v[n];
  for (int i = 0; i < m; ++i) {
    int a, b;
    cin >> a >> b;
    v[--a].push_back({--b, 1});
    from[a]++;
    to[b]++;
  }
  vector<int> q;
  for (int i = 0; i < n; ++i) {
    if (!to[i] && from[i]) q.push_back(i);
  }
  int result = 0;
  for (int qi = 0; qi < q.size(); ) {
    int i = q[qi];
    int cn = i;
    int asd = 0;
    while (from[cn]) {
      for (pair<int, int> &cv : v[cn]) {
        if (!cv.S) continue;
        cv.S = 0;
        from[cn]--;
        to[cv.F]--;
        cn = cv.F;
        if (!to[cn] && from[cn]) q.push_back(cn);
        asd = 1;
        break;
      }
    }
    result += asd;
    if (!from[i]) qi++;
  }
  cout << result << endl;
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: ACCEPTED

Test 12

Group: 3

Verdict: ACCEPTED

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED