Envío 2591

Código

#include <bits/stdc++.h>

#include <queue>
#include <vector>

using namespace std;

struct Node {
  int val;
  vector<int> neighbors;
  Node(int x) : val(x) {}
};

bool helper(int index, vector<Node *> &lookup, vector<bool> &visited,
            vector<bool> &visitedOrder) {
  if (visited[index] == false) {
    visited[index] = true;
    visitedOrder[index] = true;

    auto neighbors =  lookup[index]->neighbors;
    for (int i = 0; i < neighbors.size(); ++i) {
        auto neighborIndex = neighbors[i];
        auto neighbor = lookup[neighborIndex];

        if (visited[neighborIndex] == false and helper(neighborIndex, lookup, visited, visitedOrder)){
            return true;
        } else if (visitedOrder[neighborIndex]) {
            return true;
        }
    }
  }
  visitedOrder[index] = false;
  return false;
}

bool check_cyclic(vector<Node *> &lookup) {
  vector<bool> visited(lookup.size(), false);
  vector<bool> visitedOrder(lookup.size(), false);
  for (int i = 0; i < lookup.size(); i++) {
    if (helper(i, lookup, visited, visitedOrder)) {
      return true;
    }
  }
  return false;
}

int main() {
  int n, m;
  cin >> n >> m;
  vector<Node *> lookup(n);
  for (int i = 0; i < n; i++) {
    lookup[i] = new Node(i);
  }
  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;
    lookup[u]->neighbors.push_back(v);
  }
  if (check_cyclic(lookup)) {
    cout << "Yes" << endl;
  } else {
    cout << "No" << endl;
  }
  return 0;
}