e-olymp: Find a Cycle

#include <algorithm>
#define push_back pb
#include <string>
#include <vector>
#include <iostream>
using namespace std;

vector<int> g[100005];
int parent[100005];
int visited[100005];
vector<int> path;
vector<int> a;

int cycle, cycle_begin, cycle_end;
void dfs(int s) {
    visited[s] = 1;
    for (int i=0; i < g[s].size(); i++) {
        if (visited[g[s][i]] == 0) { parent[g[s][i]] = s; dfs(g[s][i]); }
        else if (visited[g[s][i]] == 1) { cycle = 1; cycle_begin = g[s][i]; cycle_end = s; }
    }
    visited[s] = 2;
}

int main() {
    int n, m;
    cin >> n >> m;
    for (int i=0; i<m; i++) {
        int a, b;
        cin >> a >> b;
        g[a].pb(b);
    }

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

    if (cycle == 1) {
        cout << "YES" << endl;

        while (cycle_end != cycle_begin) {
            a.pb(cycle_end);
            cycle_end = parent[cycle_end];
        }

        a.pb(cycle_begin);
        reverse(a.begin(), a.end());

        for (int i=0; i < a.size(); i++) {
            cout << a[i] << " ";
        }
    }

    else {
        cout << "NO" << endl;
    }

    return 0;
}