#include "islands.h"
#include <bits/stdc++.h>
#define pii pair<int, int>
#define fi first
#define se second
#define all(a) a.begin(), a.end()
#define rep(a,b,c) for(int a=b; a<c; a++)
#define repa(a,b) for(auto a:b)
#define repr(a,b,c) for(int a=b-1; a>c-1; a--)
#define pb push_back
using namespace std;
using vi = vector<int>;
const int N=1e5+5;
bool vis[N];
vector<pii> adj[N], radj[N];
variant<bool, vi> find_journey(int n, int m, vi U, vi V) {
int odg[n]{};
rep(i,0,m){
odg[U[i]]++;
adj[U[i]].pb({V[i],i});
radj[V[i]].pb({U[i],i});
}
vi bfcycle, cycle, afcycle, ans;
int u=-1, s=0;
while(odg[s]==1){
vis[s]=true;
bfcycle.pb(adj[s][0].se);
afcycle.pb(adj[s][0].se);
if(vis[adj[s][0].fi]) break;
u=s;
s=adj[s][0].fi;
}
queue<int> q;
if(u!=-1) q.push(u), vis[u]=true;
rep(i,0,n) if(!odg[i]) q.push(i), vis[i]=true;
while(q.size()){
u=q.front();
q.pop();
vis[u]=true;
repa(v,radj[u]){
odg[v.fi]--;
assert(odg[v.fi]>=0);
if(!odg[v.fi] && !vis[v.fi]) q.push(v.fi), vis[v.fi]=true;
}
}
fill(vis,vis+n,0);
rep(i,0,n) adj[i].clear(), radj[i].clear();
if(odg[s]<2) return false;
return true;
reverse(all(afcycle));
repa(e,bfcycle) ans.pb(e);
repa(e,cycle) ans.pb(e);
repa(e,afcycle) ans.pb(e);
return ans;
}
