#include "islands.h"
#include <algorithm>
#include <iostream>
#include <numeric>
#include <cassert>
#include <variant>
#include <vector>
typedef long long llong;
const int MAXN = 100000 + 10;
const int INF = 1e9;
int n, m;
int vis[MAXN];
std::vector <int> cycle;
std::vector <std::pair <int,int>> g[MAXN];
bool findCycleFirst(int node, int par)
{
vis[node] = 1;
for (const auto &[x, idx] : g[node])
{
if (par == idx)
{
continue;
}
if (x == 1)
{
cycle.push_back(idx);
return true;
}
if (vis[x])
{
continue;
}
if (findCycleFirst(x, idx))
{
cycle.push_back(idx);
return true;
}
}
return false;
}
std::variant <bool, std::vector<int>> find_journey(int N, int M, std::vector <int> U, std::vector <int> V)
{
n = N; m = M;
bool isFirst = !(m & 1);
bool isSecond = !(m & 1);
for (int i = 0 ; i < m ; ++i)
{
U[i]++;
V[i]++;
if (i & 1)
{
isFirst &= (U[i] == V[i - 1] && V[i] == U[i - 1]);
isSecond &= (U[i] == U[i - 1] && U[i] == U[i - 1]);
}
}
if (n == 2)
{
int cntOne = 0;
int cntTwo = 0;
std::vector <int> one;
std::vector <int> two;
for (int i = 0 ; i < m ; ++i)
{
if (U[i] == 1)
{
cntOne++;
one.push_back(i);
} else
{
cntTwo++;
two.push_back(i);
}
}
if (cntOne >= 2 && cntTwo >= 1)
{
return std::vector <int> ({one[0], two[0], one[1], one[0], two[0], one[1]});
}
return false;
}
if (isFirst)
{
for (int i = 0 ; i < m ; i += 2)
{
g[U[i]].push_back({V[i], i});
g[U[i + 1]].push_back({V[i + 1], i + 1});
}
bool isCycle = findCycleFirst(1, 0);
if (!isCycle)
{
return false;
}
std::vector <int> ans;
std::reverse(cycle.begin(), cycle.end());
for (const int &i : cycle)
{
ans.push_back(i);
}
std::reverse(cycle.begin(), cycle.end());
for (const int &i : cycle)
{
ans.push_back(i ^ 1);
}
for (const int &i : cycle)
{
ans.push_back(i);
}
std::reverse(cycle.begin(), cycle.end());
for (const int &i : cycle)
{
ans.push_back(i ^ 1);
}
return ans;
}
return false;
}
