Road network

#include <vector>
#include <iostream>
#include <queue>


int main(void) {
  int n, m;

  std::ios_base::sync_with_stdio(false);

  std::cin >> n;
  std::cin >> m;

  std::vector<std::vector<int>> routes(n + 1);

  for (int i = 0; i < m; ++i) {
    int a;
    int b;

    std::cin >> a;
    std::cin >> b;

    routes[a].push_back(b);
  }

  std::vector<bool> solution(n + 1);

  // If we've reached the intersection from the
  // currently processed node. It is written into
  // the array, if we haven't reached that node it will
  // be out of date
  std::vector<int> reached(n + 1);

  for (int i = 1; i < n + 1; ++i) {
    std::queue<int> q;
    std::vector<int> visited;

    q.push(i);

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

      reached[node] = i;
      visited.push_back(node);

      // If we can already reach every other node from this one, stop
      if (solution[node]) {
        solution[i] = true;
        //for (auto v : visited) {
        //  solution[v] = true;
        //}
        break;
      }

      for (int c : routes[node]) {
        if (reached[c] != i) {
          q.push(c);
        }
      }
    }

    if (solution[i]) {
      continue;
    }

    for (int r = 1; r < n + 1; ++r) {
      if (reached[r] != i) {
        std::cout << "NO" << std::endl;
        std::cout << i << " " << r << std::endl;
        return 0;
      }
    }

    solution[i] = true;
  }

  std::cout << "YES" << std::endl;
  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