#include "islands.h"
#include <bits/stdc++.h>
#define N 100005
using namespace std;
vector<pair<int,pair<int,int>>> adj[N];
map<int,vector<int>> mp[N];
int par[N];
int par2[N];
int vis[N];
vector<int> ans;
void dfs(int v,int pr){
vis[v] = 1;
vector<pair<int,pair<int,int>>> tmp;
for(auto u:adj[v]){
if(ans.size())
return;
if(u.second.second == pr)
continue;
if(vis[u.first] == 2)
continue;
tmp.push_back(u);
}
if(tmp.size() > 1){
int now = v;
while(now != 0){
ans.push_back(par[now]);
now = par2[now];
}
reverse(ans.begin(),ans.end());
ans.push_back(tmp[0].second.first);
ans.push_back(tmp[0].second.second);
ans.push_back(tmp[1].second.first);
ans.push_back(tmp[1].second.second);
ans.push_back(tmp[0].second.second);
ans.push_back(tmp[0].second.first);
ans.push_back(tmp[1].second.second);
ans.push_back(tmp[1].second.first);
now = v;
while(now != 0){
ans.push_back(par[now]);
now = par2[now];
}
return;
}
else{
for(auto u:adj[v]){
if(ans.size())
return;
if(vis[u.first])
continue;
par[u.first] = u.second.first;
par2[u.first] = v;
dfs(u.first,u.second.first);
}
}
vis[v] = 2;
}
void dfs2(int v,int pr){
vis[v] = 1;
// cout << v << ' ' << par2[v] << endl;
vector<pair<int,pair<int,int>>> tmp;
for(auto u:adj[v]){
if(ans.size())
return;
if(vis[u.first] == 2){
continue;
}
if(vis[u.first] == 1){
if(ans.size())
return;
// cout << u.first << "ASDa" << v << endl;
int now = u.first;
while(now != 0){
ans.push_back(par[now]);
now = par2[now];
}
reverse(ans.begin(),ans.end());
vector<int> v1 = {},v2 = {};
now = v;
int cnt = 0;
int sz = 1;
while(now != u.first){
assert(cnt++ <= 1000);
v1.push_back(par[now]);
v2.push_back(par[now] + 1);
sz++;
// cout << now << endl;
now = par2[now];
}
reverse(v1.begin(),v1.end());
reverse(v2.begin(),v2.end());
v1.push_back(u.second.first);
v2.push_back(u.second.first + 1);
assert(sz >= 2);
for(auto c:v1){
ans.push_back(c);
}
for(auto c:v2){
ans.push_back(c);
}
reverse(v1.begin(),v1.end());
reverse(v2.begin(),v2.end());
for(auto c:v1){
ans.push_back(c);
}
for(auto c:v2){
ans.push_back(c);
}
now = u.first;
while(now != 0){
ans.push_back(par[now]);
now = par2[now];
}
return;
}
par[u.first] = u.second.first;
par2[u.first] = v;
dfs2(u.first,u.second.first);
}
vis[v] = 2;
}
variant<bool, vector<int>> find_journey(int n, int m, vector<int> U, vector<int> V){
if(n == 2){
for(int i = 0;i<m;i++){
mp[U[i]][V[i]].push_back(i);
}
if(mp[0][1].size() < 2 || mp[1][0].size() < 1)
return false;
int a = mp[0][1][0];
int b = mp[0][1][1];
int c = mp[1][0][0];
ans = {a,c,b,a,c,b};
return ans;
}
bool subtask4 = (m + 1)%2;
for(int i = 0;i<m && subtask4;i+=2){
if(U[i] != U[i+1] || V[i] != V[i+1])
subtask4 = 0;
}
if(subtask4){
for(int i = 0;i<m;i+=2){
adj[U[i]].push_back({V[i],{i,i+1}});
// cout << U[i] << ' ' << V[i] << endl;
}
dfs2(0,-1);
if(!ans.size())
return false;
return ans;
}
for(int i = 0;i<m;i++){
if(mp[V[i]][U[i]].size()){
adj[U[i]].push_back({V[i],{i,mp[V[i]][U[i]].back()}});
adj[V[i]].push_back({U[i],{mp[V[i]][U[i]].back(),i}});
mp[V[i]][U[i]].pop_back();
}else{
mp[U[i]][V[i]].push_back(i);
}
}
dfs(0,-1);
if(ans.empty())
return false;
return ans;
}
