#include "islands.h"
#include <bits/stdc++.h>
using namespace std;
vector<vector<int>> adj;
vector<int> pai, marc, rep, ans;
map<int, map<int, int>> mp;
void dfs( int cur, int pai ){
int f1 = -1, f2 = -1;
for( int viz : adj[cur] ) if( viz != pai ){
if( f1 == -1 ) f1 = viz;
else f2 = viz;
}
if( f2 != -1 ){
int tam = ans.size();
ans.push_back(mp[cur][f1]);
ans.push_back(mp[f1][cur]);
ans.push_back(mp[cur][f2]);
ans.push_back(mp[f2][cur]);
ans.push_back(mp[f1][cur]);
ans.push_back(mp[cur][f1]);
ans.push_back(mp[f2][cur]);
ans.push_back(mp[cur][f2]);
for( int i = tam - 1; i >= 0; i-- ) ans.push_back(ans[i]);
return;
}
if( f2 == -1 ){
ans.push_back(mp[cur][f1]);
dfs( f1, cur);
ans.pop_back();
}
}
variant<bool, vector<int>> find_journey( int n, int m, vector<int> a, vector<int> b ){
adj.resize(n);
marc.resize(n);
pai.resize(n);
rep.resize(n);
iota( rep.begin(), rep.end(), 0 );
for( int i = 0; i < m; i++ ){
adj[a[i]].push_back(b[i]);
mp[a[i]][b[i]] = i;
}
dfs( 0,-1 );
if( ans.empty() ) return false;
return ans;
}
