#include "islands.h"
#include <bits/stdc++.h>
using namespace std;
vector<vector<array<int, 2>>> g, rg;
vector<int> color, par, del, deg;
map<int, int> cache;
int dfs(int u, int p){
par[u] = p;
color[u] = 1;
for(auto [v, e]:g[u]){
if(v==p){
deg[u]--;
}
}
if(deg[u]>1)
return 1;
bool ok = 0;
for(auto [v, e]:g[u]){
if(del[v] or color[v])
continue;
ok |= dfs(v, u);
}
return ok;
}
std::variant<bool, std::vector<int>> find_journey(int N, int M, std::vector<int> U, std::vector<int> V) {
g.assign(N, {});
rg.assign(N, {});
color.assign(N, {});
par.assign(N, {});
del.assign(N, {});
deg.assign(N, {});
for(int i=0; i<M; i++){
g[U[i]].push_back({V[i], i});
rg[V[i]].push_back({U[i], i});
}
queue<int> q;
for(int i=0; i<N; i++){
deg[i]=g[i].size();
if(deg[i]==0){
q.push(i);
}
}
while(q.size()){
auto u = q.front();
q.pop();
del[u]=1;
for(auto [v, e]:rg[u]){
if(--deg[v]==0){
q.push(v);
}
}
}
return dfs(0, 0)==1;
}
