#include "islands.h"
#include <bits/stdc++.h>
#include <variant>
using namespace std;
int n, m, X, Y, I = -1;
vector<int> u;
vector<int> v;
vector<vector<int> > g(2e5);
vector<int> e(2e5, -1);
vector<int> oda;
vector<int> kor;
vector<int> ans;
void solve1() {
vector<int> a;
vector<int> b;
for (int i = 0; i < m; i++) {
if (!u[i]) a.push_back(i);
else b.push_back(i);
}
if (a.size() < 2 || b.size() < 1) return;
ans = {a[0], b[0], a[1], a[0], b[0], a[1]};
}
void solve2() {
ans.resize(12);
for (int i = 0; i < m; i++) {
if (u[i] == 0 && v[i] == 1) ans[0] = ans[8] = i;
if (u[i] == 1 && v[i] == 0) ans[5] = ans[9] = i;
if (u[i] == 0 && v[i] == 2) ans[3] = ans[11] = i;
if (u[i] == 2 && v[i] == 0) ans[2] = ans[6] = i;
if (u[i] == 1 && v[i] == 2) ans[1] = ans[7] = i;
if (u[i] == 2 && v[i] == 1) ans[4] = ans[10] = i;
}
}
void dfs3(int x) {
for (int i: g[x]) {
if (i == (e[x] ^ 1)) continue;
int y = v[i];
if (e[y] > -1) {
X = x;
Y = y;
I = i;
continue;
}
e[y] = i;
dfs3(y);
}
}
void solve3() {
for (int i = 0; i < m; i++) g[u[i]].push_back(i);
e[0] = m;
dfs3(0);
if (I == -1) return;
kor.push_back(I);
swap(X, Y);
while (X != Y) {
kor.push_back(e[X]);
X = u[e[X]];
}
while (X) {
oda.push_back(e[X]);
X = u[e[X]];
}
reverse(oda.begin(), oda.end());
for (int i: oda) ans.push_back(i);
for (int i: kor) ans.push_back(i);
reverse(kor.begin(), kor.end());
for (int i: kor) ans.push_back(i ^ 1);
for (int i: kor) ans.push_back(i);
reverse(kor.begin(), kor.end());
for (int i: kor) ans.push_back(i ^ 1);
reverse(oda.begin(), oda.end());
for (int i: oda) ans.push_back(i);
}
void solve4() {
}
variant<bool, vector<int> > find_journey(int N, int M, vector<int> U, vector<int> V) {
n = N;
m = M;
u = U;
v = V;
bool st3 = true, st4 = true;
if (m % 2) st3 = st4 = false;
for (int i = 0; i < m - 1; i += 2) {
if (u[i] != v[i + 1]) st3 = false;
if (v[i] != u[i + 1]) st3 = false;
if (u[i] != u[i + 1]) st4 = false;
if (v[i] != v[i + 1]) st4 = false;
}
if (n == 2) solve1();
else if (st3) solve3();
else if (st4) solve4();
else solve2();
if (ans.size()) return ans;
return false;
}
