#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)
{
int u=0;
vector<pair<int,int>> nei[n];
vector<int> v;
bool vis[n]={};
for (int i=0;i<m;i+=2)
nei[U[i]].push_back({V[i],i});
while (1)
{
int f=-1,s=-1,id,id1;
vis[u]=1;
for (auto [i,x]:nei[u])
if (!vis[i])
{
if (f==-1) f=i,id=x;
else s=i,id1=x;
}
if (f==-1)
return false;
if (~s)
{
vector<int> v1=v;
v.push_back(id), v.push_back(id+1);
v.push_back(id1), v.push_back(id1+1);
v.push_back(id+1), v.push_back(id);
v.push_back(id1+1), v.push_back(id1);
while (!v1.empty())
v.push_back(v1.back()), v1.pop_back();
return v;
}
else
v.push_back(id),u=f;
}
}
