#include "islands.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
#define all(x) x.begin(), x.end()
#define sz(x) (int)x.size()
#define pb push_back
#define mk make_pair
#define fr first
#define sc second
vector<int> ord, vis, valid;
vector<vector<pii>> edges, tedges;
void dfs(int x) {
vis[x] = 1;
for(auto [viz,ind] : edges[x])
if(!vis[viz]) dfs(viz);
ord.pb(x);
}
void find_scc(int x) {
vis[x] = 1;
for(auto [viz, ind] : tedges[x]) {
if(!vis[viz]) {
valid[x] = valid[viz] = 1;
find_scc(viz);
}
}
}
vector<int> at;
vector<int> ciclo(int x, int raiz) {
vis[x] = 1;
for(auto [viz,ind] : edges[x]) {
if(viz == raiz) {
at.pb(ind);
return at;
}
if(!vis[viz]) {
at.pb(ind);
vector<int> v = ciclo(viz, raiz);
if(!v.empty()) return v;
}
}
return {};
}
variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
edges.resize(N);
tedges.resize(N);
vis.resize(N);
valid.resize(N);
for(int i = 0; i < M; i++) edges[U[i]].pb({V[i], i}), tedges[V[i]].pb({U[i], i});
//cout << "OK" << endl;
for(int i = 0; i < N; i++)
if(!vis[i]) dfs(i);
reverse(all(ord));
vis.clear(); vis.resize(N);
for(auto x : ord)
if(!vis[x]) find_scc(x);
// agora basta ver se tem como chegar em um no valido de 2 formas
vector<vector<pii>> s(N);
queue<tuple<int,int,int>> fila;
fila.push({0,-1,-1});
while(!fila.empty()) {
auto [x, s_e, pai_edge] = fila.front();
fila.pop();
if(sz(s[x]) >= 2) continue;
if(sz(s[x]) == 1 and s[x][0].fr == s_e) continue;
if(s_e != -1) s[x].pb({s_e, pai_edge});
for(auto [viz, ind] : edges[x]) {
if(s_e == -1) fila.push({viz, ind, ind});
else fila.push({viz, s_e, ind});
}
}
for(int i = 0; i < N; i++) {
if(sz(s[i]) >= 2 and valid[i]) {
vis.clear();
vis.resize(N);
vector<int> c = ciclo(i, i), ans, cam1, cam2;
for(int x = i; ; ) {
if(s[x][0].fr == s[i][0].fr) cam1.pb(s[x][0].sc), x = U[s[x][0].sc];
else cam1.pb(s[x][1].sc), x = U[s[x][1].sc];
if(x == 0) break;
}
for(int x = i; ; ) {
if(s[x][0].fr == s[i][1].fr) cam2.pb(s[x][0].sc), x = U[s[x][0].sc];
else cam2.pb(s[x][1].sc), x = U[s[x][1].sc];
if(x == 0) break;
}
reverse(all(cam1));
for(auto x : cam1) ans.pb(x);
for(auto x : c) ans.pb(x);
reverse(all(cam1));
for(auto x : cam1) ans.pb(x);
reverse(all(cam2));
for(auto x : cam2) ans.pb(x);
reverse(all(c));
for(auto x : c) ans.pb(x);
reverse(all(cam2));
for(auto x : cam2) ans.pb(x);
return ans;
}
}
return false;
}
