Envío 4013

Código

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

#define endl '\n'
#define ll long long
#define sz(x) int(x.size())
#define dbg(x) cout << #x << " = " << x << endl

int n, m;
vector<vector<int>> ady;
vector<int> color;


bool dfs(int v) {
    color[v] = 1;
    for (int &u: ady[v]) {
        if (color[u] == 1) {
            return true;
        } else if (color[u] == 0) {
            return dfs(u);
        }
    }
    color[v] = 2;
    return false;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> m;
    ady.resize(n);
    color.resize(n);

    while (m--) {
        int v, u; cin >> v >> u;
        ady[v].push_back(u);
    }

    bool flag = false;
    for (int i = 0; i < n; ++i) {
        if (color[i] == 0) {
            if (dfs(i)) {
                flag = true;
                break;
            }
        }
    }
    if (flag) cout << "Yes" << endl;
    else cout << "No" << endl;
    return 0;
}