// failed/solution-ayaze-double-edge.cpp
#include "islands.h"
#include <bits/stdc++.h>
using namespace std;
std::variant<bool, std::vector<int>> find_journey(
int N, int M, std::vector<int> U, std::vector<int> V) {
vector<vector<pair<int, int>>> adj_list(N);
for (int i = 0 ; i < M ; i++) {
adj_list[U[i]].push_back({V[i], i});
}
vector<int> parent(N, -1);
vector<int> in_num(N), out_num(N);
int num_cntr = 0;
parent[0] = 0;
function<void(int)> dfs = [&](int now) {
in_num[now] = ++num_cntr;
for (auto [nex, _] : adj_list[now]) {
if (parent[nex] == -1) {
parent[nex] = now;
dfs(nex);
}
}
out_num[now] = num_cntr;
};
dfs(0);
vector<int> path;
int cyclic_point = -1;
int end_point = -1;
for (int i = 1 ; i < N ; i++) {
if (parent[i] == -1) continue;
for (auto [nex, _] : adj_list[i]) {
if (in_num[nex] <= in_num[i] && in_num[i] <= out_num[nex]) {
end_point = i;
cyclic_point = nex;
break;
}
}
}
if (cyclic_point == -1) {
return false;
}
path = {cyclic_point};
for (int v = end_point ; v != 0 ; v = parent[v]) {
path.push_back(v);
}
path.push_back(0);
reverse(path.begin(), path.end());
vector<vector<int>> path_edges;
for (int i = 0 ; i+1 < static_cast<int>(path.size()) ; i++) {
int j = i+1;
vector<int> edges;
for (auto [v, edge_idx] : adj_list[path[i]]) {
if (v == path[j]) {
edges.push_back(edge_idx);
}
}
path_edges.push_back(edges);
}
vector<int> ret;
int path_edges_size = path_edges.size();
if (cyclic_point == 0) { // full cycle
for (int i = 0 ; i < path_edges_size ; i++) {
ret.push_back(path_edges[i][0]);
}
for (int i = 0 ; i < path_edges_size ; i++) {
ret.push_back(path_edges[i][1]);
}
for (int i = path_edges_size-1 ; i >= 0 ; i--) {
ret.push_back(path_edges[i][0]);
}
for (int i = path_edges_size-1 ; i >= 0 ; i--) {
ret.push_back(path_edges[i][1]);
}
} else {
int first_cyclic_occ = -1;
for (int i = 0 ; i < path_edges_size ; i++) {
if (path[i] == cyclic_point) {
first_cyclic_occ = i;
break;
}
}
for (int i = 0 ; i < path_edges_size ; i++) {
ret.push_back(path_edges[i][0]);
}
for (int i = first_cyclic_occ-1 ; i >= 0 ; i--) {
ret.push_back(path_edges[i][0]);
}
for (int i = 0 ; i < first_cyclic_occ ; i++) {
ret.push_back(path_edges[i][1]);
}
for (int i = path_edges_size-1 ; i >= first_cyclic_occ ; i--) {
ret.push_back(path_edges[i][0]);
}
for (int i = first_cyclic_occ-1 ; i >= 0 ; i--) {
ret.push_back(path_edges[i][1]);
}
}
return ret;
}
