#include "islands.h"
#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define rep2(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rrep(i, n) for (int i = (int)(n) - 1; i >= 0; --i)
#define rrep2(i, a, b) for (int i = (int)(b) - 1; i >= (int)(a); --i)
#define all(v) begin(v), end(v)
#define rall(v) rbegin(v), rend(v)
using namespace std;
using ll = long long;
template<class T, class U> bool chmin(T& a, const U& b) { return a > b ? a = b, true : false; }
template<class T, class U> bool chmax(T& a, const U& b) { return a < b ? a = b, true : false; }
struct edge {
int to, idx;
};
using Graph = vector<vector<edge>>;
std::variant<bool, std::vector<int>> find_journey(int N, int M, std::vector<int> U, std::vector<int> V) {
Graph G(N);
rep (i, M) G[U[i]].push_back({V[i], i});
queue<int> que;
vector<bool> seen(N, false), used(N, false);
vector<bool> cycle1(N, false);
que.push(0);
while (!que.empty()) {
int s = -1;
bool flag = false;
vector<int> cs;
auto dfs = [&](auto&& self, int v) -> void {
seen[v] = used[v] = true;
for (auto e : G[v]) {
if (used[e.to]) {
if (s == -1) {
s = e.to;
cycle1[v] = true;
cs.push_back(v);
break;
}
else {
flag = true;
break;
}
}
if (cycle1[e.to]) {
flag = true;
break;
}
if (seen[e.to]) continue;
self(self, e.to);
if (flag) break;
if (s >= 0) {
cycle1[v] = true;
cs.push_back(v);
if (s != v) break;
s = -2;
}
}
used[v] = false;
};
int v = que.front(); que.pop();
dfs(dfs, v);
if (flag) return true;
for (int i : cs) cycle1[i] = false;
for (int i : cs) if (i != cs.back()) que.push(i);
}
return false;
}
