#include "islands.h"
#include <variant>
#include<bits/stdc++.h>
#define all(v) v.begin(),v.end()
using namespace std;
using ll = long long;
using P = pair<ll, ll>;
using PP = pair<ll, P>;
const ll n_ = 2e5 + 505, inf = (ll)2e9 * (ll)1e9 + 7, mod = 998244353;
ll n, m, tc = 1, a, b, c, d, sum, x, y, z, base, ans, k;
vector<ll>rev[n_];
ll prob[n_],out[n_];
set<ll>v[n_];
variant<bool, std::vector<int>> find_journey(int N, int M, std::vector<int> U, std::vector<int> V) {
n=N,m=M;
for(int i=0;i<m;i++){
out[U[i]]++;
v[U[i]].insert(V[i]);
rev[V[i]].push_back(U[i]);
}
fill(prob,prob+n+1,1);
//가능성이 존재한다.
queue<ll>q;
for(int i=1;i<=n;i++){
if(out[i])continue;
q.push(i);
}
while(q.size()){
a=q.front();
q.pop();
prob[a]=0;
for(auto nxt:rev[a]){
out[nxt]--;
v[nxt].erase(a);
if(out[nxt]==0){
q.push(nxt);
}
}
}
ll now=0;
vector<int>ret,ret_rev;
while(1){
if(!out[now])return false;
if(out[now]==1){
ret.push_back(now);
ret_rev.push_back(now);
queue<ll>q;
for(auto nxt:rev[now]){
out[nxt]--;
v[nxt].erase(now);
if(out[nxt]==0)q.push(nxt);
}
out[now]=0;
now=*v[now].begin();
}
else{
return true;
break;
}
}
reverse(all(ret_rev));
for(auto i:ret_rev)ret.push_back(i);
return ret;
}
