#include "islands.h"
#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
const int M=2e5+5;
int n,m;
vector<pair<int,int>> adj[N];
vector<int> path;
bool vis[N],vis2[N];
int dfs(int u){
if(vis2[u])return u;
if(vis[u])return -1;
vis[u]=vis2[u]=true;
for(auto [v,id]:adj[u]){
path.emplace_back(id);
int res=dfs(v);
if(res!=-1)return res;
path.pop_back();
}
vis2[u]=false;
return -1;
}
variant<bool, vector<int>> find_journey(int N,int M,vector<int> U,vector<int> V){
n=N,m=M;
for(int i=0;i<m;i+=2)adj[U[i]].emplace_back(V[i],i);
int res=dfs(0);
if(res==-1)return false;
auto ans=path;
vector<int> path2;
stack<int> rev;
int cur=0;
bool ok=false;
for(auto i:path){
if(cur==res)ok=true;
if(!ok){
rev.emplace(i);
}else{
path2.emplace_back(i);
}
cur=V[i];
}
for(auto i:path2){
ans.emplace_back(i+1);
}
reverse(path2.begin(),path2.end());
for(auto i:path2){
ans.emplace_back(i);
}
for(auto i:path2){
ans.emplace_back(i+1);
}
while(!rev.empty()){
ans.emplace_back(rev.top());
rev.pop();
}
return ans;
}
