#include "islands.h"
#include <bits/stdc++.h>
#include <variant>
using namespace std;
#define rall(s) s.rbegin(), s.rend()
#define all(s) s.begin(), s.end()
#define sz(s) (int) s.size()
#define s second
#define f first
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int N = 3e5;
vector<pii> g[N], pr(N);
vector<int> was(N), s;
void dfs(int u, int x) {
was[u] = 1;
for (auto [to, id]: g[u]) {
if (id == x) continue;
if (!was[to]) {
pr[to] = {u, id};
dfs(to, x);
if (sz(s)) return;
}else if (!to) {
s.push_back(id);
while (u) {
s.push_back(pr[u].s);
u = pr[u].f;
}
return;
}
}
}
variant<bool, vector<int>> find_journey(int n, int m, vector<int> u, vector<int> v) {
for (int i = 0; i < m; i++) g[u[i]].push_back({v[i], i});
for (auto [to, id]: g[0]) {
was[0] = 1;
dfs(to, id ^ 1);
if (sz(s)) return true;
for (int i = 0; i < n; i++) {
was[i] = 0;
}
}
return false;
reverse(all(s));
vector<int> ans;
for (int x: s) ans.push_back(x);
}
