#include "islands.h"
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(a, b) for(int a = 0; a < (b); ++a)
#define st first
#define nd second
#define pb push_back
#define all(a) a.begin(), a.end()
const int LIM=1e5+7;
vector<int>V[LIM], S[LIM];
int deg[LIM], odw[LIM], n, m;
variant<bool,vector<int>>find_journey(int _n, int _m, vector<int>_u, vector<int>_v) {
n=_n; m=_m;
rep(i, m) {
V[_u[i]].pb(_v[i]);
S[_v[i]].pb(_u[i]);
}
rep(i, n) deg[i]=V[i].size();
queue<int>q;
rep(i, n) if(deg[i]==0) {
odw[i]=1;
q.push(i);
}
int akt=0;
while(true) {
if(deg[akt]<1 || odw[akt]) return false;
if(deg[akt]==1) {
odw[akt]=1;
int p=-1;
for(auto i : V[akt]) if(!odw[i]) p=i;
if(p==-1) return false;
for(auto i : S[akt]) {
--deg[i];
if(deg[i]<=1 && !odw[i]) {
odw[i]=1;
q.push(i);
}
}
akt=p;
continue;
}
if(q.empty()) break;
int p=q.front(); q.pop();
for(auto i : S[p]) {
--deg[i];
if(deg[i]<=1 && !odw[i]) {
odw[i]=1;
q.push(i);
}
}
}
return true;
}
