#include "islands.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define sp <<" "<<
#define endl "\n"
variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
vector<vector<pair<int, int>>> adj(N), rev(N);
for (int i = 0; i < M; i+=2) {
adj[U[i]].emplace_back(V[i], i);
}
// st3 / st4
// FIND ANY CYCLE. note that for st3/4 we can just topo sort no?
vector<bool> vis(N), proc(N);
bool found = false;
int st = -1, en = -1;
vector<pair<int, int>> par(N, make_pair(-1, -1));
vector<int> path, cyc;
auto dfs = [&](auto &&dfs, int u) -> void {
if (found) return;
vis[u] = proc[u] = true;
for (auto &[v, x] : adj[u]) {
if (vis[v] and proc[v]) {
found = true;
st = v;
en = u;
cyc.push_back(x);
return;
}
if (!vis[v]) {
par[v] = make_pair(u, x);
dfs(dfs, v);
}
}
proc[u] = false;
};
dfs(dfs, 0);
if (!found) return false;
int at = en;
while (par[at].first != -1 and at != st) {
cyc.push_back(par[at].second);
at = par[at].first;
}
while (par[at].first != -1) {
path.push_back(par[at].second);
at = par[at].first;
}
// cerr << "Here" << endl;
// subtask 3
vector<int> ans;
int n = cyc.size(), m = path.size();
for (int i = m-1; i >= 0; i--) {
ans.push_back(path[i]);
}
for (int i = n-1; i >= 0; i--) {
ans.push_back(cyc[i]);
}
for (int i = n-1; i >= 0; i--) {
ans.push_back(cyc[i]+1);
}
for (int i = 0; i < n; i++) {
ans.push_back(cyc[i]);
}
for (int i = 0; i < n; i++) {
ans.push_back(cyc[i]+1);
}
for (int i = 0; i < m; i++) {
ans.push_back(path[i]);
}
return ans;
}
