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View the Project on GitHub kmyk/competitive-programming-library
#define PROBLEM "https://yukicoder.me/problems/no/1254"
#include <algorithm>
#include <cstdio>
#include <map>
#include <utility>
#include <vector>
#include "../utils/macros.hpp"
#include "../graph/functional_graph.hpp"
using namespace std;
vector<int> solve(int n, const vector<pair<int, int> >& edges) {
vector<vector<int> > g(n);
map<pair<int, int>, int> lookup;
REP (i, edges.size()) {
auto [a, b] = edges[i];
g[a].push_back(b);
g[b].push_back(a);
lookup[make_pair(a, b)] = i;
lookup[make_pair(b, a)] = i;
}
auto cycle = get_namori_cycle(g);
vector<int> ans;
REP (i, cycle.size()) {
int a = cycle[i];
int b = cycle[(i + 1) % cycle.size()];
ans.push_back(lookup[make_pair(a, b)]);
}
sort(ALL(ans));
return ans;
}
int main() {
int n; scanf("%d", &n);
vector<pair<int, int> > edges(n);
REP (i, n) {
int a, b; scanf("%d%d", &a, &b);
-- a;
-- b;
edges[i] = make_pair(a, b);
}
vector<int> ans = solve(n, edges);
printf("%d\n", (int)ans.size());
REP (i, ans.size()) {
printf("%d%c", ans[i] + 1, i + 1 < ans.size() ? ' ' : '\n');
}
return 0;
}
#line 1 "graph/functional_graph.yuki1254.test.cpp"
#define PROBLEM "https://yukicoder.me/problems/no/1254"
#include <algorithm>
#include <cstdio>
#include <map>
#include <utility>
#include <vector>
#line 2 "utils/macros.hpp"
#define REP(i, n) for (int i = 0; (i) < (int)(n); ++ (i))
#define REP3(i, m, n) for (int i = (m); (i) < (int)(n); ++ (i))
#define REP_R(i, n) for (int i = (int)(n) - 1; (i) >= 0; -- (i))
#define REP3R(i, m, n) for (int i = (int)(n) - 1; (i) >= (int)(m); -- (i))
#define ALL(x) std::begin(x), std::end(x)
#line 2 "graph/functional_graph.hpp"
#include <cassert>
#include <deque>
#include <functional>
#line 6 "graph/functional_graph.hpp"
/**
* @brief Namori cycle / なもり閉路
* @param g a simple connected undirected graph with |E| = |V|
*/
std::deque<int> get_namori_cycle(const std::vector<std::vector<int> >& g) {
int n = g.size();
{ // check the namori-ty
int m = 0;
REP (i, n) {
m += g[i].size();
}
assert (m == 2 * n);
}
std::deque<int> stk;
std::vector<bool> used(n);
auto go = [&](auto&& go, int i, int parent) -> int {
if (used[i]) return i;
stk.push_back(i);
used[i] = true;
for (int j : g[i]) if (j != parent) {
int k = go(go, j, i);
if (k != -1) return k;
}
assert (stk.back() == i);
stk.pop_back();
used[i] = false;
return -1;
};
int i = go(go, 0, -1);
assert (i != -1); // fails if the graph is not simple
while (stk.front() != i) {
stk.pop_front();
}
return stk;
}
#line 9 "graph/functional_graph.yuki1254.test.cpp"
using namespace std;
vector<int> solve(int n, const vector<pair<int, int> >& edges) {
vector<vector<int> > g(n);
map<pair<int, int>, int> lookup;
REP (i, edges.size()) {
auto [a, b] = edges[i];
g[a].push_back(b);
g[b].push_back(a);
lookup[make_pair(a, b)] = i;
lookup[make_pair(b, a)] = i;
}
auto cycle = get_namori_cycle(g);
vector<int> ans;
REP (i, cycle.size()) {
int a = cycle[i];
int b = cycle[(i + 1) % cycle.size()];
ans.push_back(lookup[make_pair(a, b)]);
}
sort(ALL(ans));
return ans;
}
int main() {
int n; scanf("%d", &n);
vector<pair<int, int> > edges(n);
REP (i, n) {
int a, b; scanf("%d%d", &a, &b);
-- a;
-- b;
edges[i] = make_pair(a, b);
}
vector<int> ans = solve(n, edges);
printf("%d\n", (int)ans.size());
REP (i, ans.size()) {
printf("%d%c", ans[i] + 1, i + 1 < ans.size() ? ' ' : '\n');
}
return 0;
}