Поиск цикла

#include <bits/stdc++.h>

using namespace std;

const int N = 1e5 + 6;

int n, m;
int used[N], par[N];
vector <int> g[N];

void dfs(int v) {
    used[v] = 1;
    for (int i = 0; i < g[v].size(); i++) {
        int to = g[v][i];
        if (used[to] == 1) {
            cout << "YES\n";
            vector <int> path;
            int x = v;
            while (true) {
                path.push_back(x);
                if (x == to) break;
                x = par[x];
            }
            reverse(path.begin(), path.end());
            for (int i = 0; i < path.size(); i++) {
                cout << path[i] << " ";
            }
            exit(0);
        }
        if (used[to] == 0) {
            par[to] = v;
            dfs(to);
        }
    }
    used[v] = 2;
}

int main(){
    cin >> n >> m;

    for (int i = 1; i <= m; i++) {
        int a, b;
        cin >> a >> b;
        g[a].push_back(b);
    }

    for (int i = 1; i <= n; i++) {
        if (used[i] == 0) {
            dfs(i);
        }
    }

    cout << "NO\n";
}