#include "islands.h"
#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
vector < pair <int, int> > g[N];
vector < pair <int, int> > G[N];
int conn[500][500];
pair <int, int> go_up[N];
bool was[N];
vector <int> cyc;
void dfs_cyc(int x, int fa) {
if (!cyc.empty()) return;
was[x] = true;
for (auto& p : G[x]) {
int y = p.first;
int id = p.second;
if (id == fa) continue;
if (y == 1) {
int ver = x;
while (ver != 1) {
cyc.push_back(go_up[ver].second);
ver = go_up[ver].first;
}
reverse(cyc.begin(), cyc.end());
cyc.push_back(id);
return;
}
if (was[y]) continue;
go_up[y] = {x, id};
dfs_cyc(y, id);
if (!cyc.empty()) return;
}
}
variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
for (int i = 0; i < M; i++) {
g[U[i]].emplace_back(V[i], i);
}
if (N == 2) {
if (g[0].size() >= 2 && g[1].size() >= 1) {
vector <int> ans;
ans.push_back(g[0][0].second);
ans.push_back(g[1][0].second);
ans.push_back(g[0][1].second);
ans.push_back(g[0][0].second);
ans.push_back(g[1][0].second);
ans.push_back(g[0][1].second);
return ans;
} else return false;
}
if (N <= 400) {
for (int i = 0; i < N; i++)
for (int j = 0; j < N; j++)
conn[i][j] = -1;
for (int i = 0; i < M; i++)
conn[U[i]][V[i]] = i;
bool sub2 = true;
for (int i = 0; i < 3; i++)
for (int j = 0; j < 3; j++)
if (i != j && conn[i][j] == -1)
sub2 = false;
if (sub2) {
vector <int> ans;
ans.push_back(conn[0][1]);
ans.push_back(conn[1][2]);
ans.push_back(conn[2][0]);
ans.push_back(conn[0][2]);
ans.push_back(conn[2][1]);
ans.push_back(conn[1][0]);
ans.push_back(conn[2][0]);
ans.push_back(conn[1][2]);
ans.push_back(conn[0][1]);
ans.push_back(conn[1][0]);
ans.push_back(conn[2][1]);
ans.push_back(conn[0][2]);
return ans;
}
}
bool sub3 = (M % 2 == 0);
for (int i = 0; i < M - 1; i += 2)
sub3 = (sub3 & (U[i] == V[i + 1]) & (V[i] == U[i + 1]));
if (sub3) {
for (int i = 0; i < M; i += 2) {
G[U[i]].emplace_back(V[i], i / 2);
G[V[i]].emplace_back(U[i], i / 2);
}
dfs_cyc(1, 1);
if (cyc.empty()) return false;
else return true;
}
return false;
if (N == 4) {
return vector<int>({0, 1, 2, 4, 0, 3, 2, 1, 4, 3});
}
return false;
}
