#include "islands.h"
#include <bits/stdc++.h>
using namespace std;
variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
if (N == 2) {
vector<int> a, b;
for (int i = 0; i < M; i++) {
if (!U[i]) a.push_back(i);
else b.push_back(i);
}
if (a.size() < 2 || b.empty()) return false;
else return vector<int>{a[0], b[0], a[1], a[0], b[0], a[1]};
} else if (N <= 400 && M == N * (N - 1) && 0) {
int x, y, z, t;
for (int i = 0; i < M; i++) {
if (U[i] == 0 && V[i] == 1) x = i;
if (U[i] == 1 && V[i] == 0) y = i;
if (U[i] == 0 && V[i] == 2) z = i;
if (U[i] == 2 && V[i] == 0) t = i;
}
return vector<int>{x, y, z, t, y, x, t, z};
} else {
vector<set<int>> adj(N);
for (int i = 0; i < M; i++) {
adj[U[i]].insert(V[i]);
}
vector<int> vis(N);
auto dfs = [&](auto dfs, int x, int p) -> bool {
vis[x] = 1;
for (int y : adj[x]) {
if (y == p) continue;
if (vis[y] == 1) return 1;
if (!vis[y]) if (dfs(dfs, y, x)) return 1;
}
vis[x] = 2;
return 0;
};
return dfs(dfs, 0, -1);
}
}
