#include "islands.h"
#include <variant>
#include <bits/stdc++.h>
using namespace std;
#define ff first
#define ss second
#define all(a) (a).begin(), (a).end()
#define ll long long
const int mod = 1000002022;
vector<int> state, p;
int n, m;
vector<vector<int>> g;
template<typename T>
int len(T &a){return a.size();}
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
variant<bool, vector<int>> find_journey(
int n, int m, std::vector<int> u, std::vector<int> v) {
vector<vector<int>> g(n);
for(int i = 0; i < m; i ++) g[u[i]].push_back(i);
if(len(g[0]) == 0) return false;
vector<int> ans;
vector<int> vis(n);
vector<int> cyc;
vector<int> par(n);
auto dfs = [&](auto &dfs, int i)->bool{
vis[i] = 1;
for(auto j : g[i]){
if(j % 2) continue;
int x = v[j];
if(vis[x] == 2) continue;
if(vis[x] == 1){
cyc.push_back(j);
int cur = i;
while(cur != x){
cyc.push_back(par[cur]);
cur = u[par[cur]];
}
return true;
}
par[x] = j;
if(dfs(dfs, x)){
return true;
}
}
vis[i] = 2;
return false;
};
if(!dfs(dfs, 0)){
return false;
}
int j = u[cyc.back()];
//cout << j << endl;
while(j != 0){
ans.push_back(par[j]);
j = u[par[j]];
}
reverse(all(ans));
reverse(all(cyc));
vector<int> res;
for(auto i : ans) res.push_back(i);
for(auto i : cyc) res.push_back(i);
for(auto i : cyc) res.push_back(i ^ 1);
reverse(all(cyc));
for(auto i : cyc) res.push_back(i);
for(auto i : cyc) res.push_back(i ^ 1);
reverse(all(ans));
for(auto i : ans) res.push_back(i);
return res;
}
