C++ Library for Competitive Programming
/*
* @title グラフ/橋の列挙
*
* verification-helper: PROBLEM http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=GRL_3_B
*/
#include <algorithm>
#include <iostream>
#include <utility>
#include <vector>
#include "emthrm/graph/edge.hpp"
#include "emthrm/graph/enumerate_bridges.hpp"
int main() {
int v, e;
std::cin >> v >> e;
std::vector<std::vector<emthrm::Edge<bool>>> graph(v);
while (e--) {
int s, t;
std::cin >> s >> t;
graph[s].emplace_back(s, t);
graph[t].emplace_back(t, s);
}
std::vector<emthrm::Edge<bool>> bridges = emthrm::enumerate_bridges(graph);
std::ranges::sort(bridges.begin(), bridges.end(), {},
[](const emthrm::Edge<bool>& e) -> std::pair<int, int> {
return std::make_pair(e.src, e.dst);
});
for (const emthrm::Edge<bool>& bridge : bridges) {
std::cout << bridge.src << ' ' << bridge.dst << '\n';
}
return 0;
}
#line 1 "test/graph/enumerate_bridges.test.cpp"
/*
* @title グラフ/橋の列挙
*
* verification-helper: PROBLEM http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=GRL_3_B
*/
#include <algorithm>
#include <iostream>
#include <utility>
#include <vector>
#line 1 "include/emthrm/graph/edge.hpp"
/**
* @title 辺
*/
#ifndef EMTHRM_GRAPH_EDGE_HPP_
#define EMTHRM_GRAPH_EDGE_HPP_
#include <compare>
namespace emthrm {
template <typename CostType>
struct Edge {
CostType cost;
int src, dst;
explicit Edge(const int src, const int dst, const CostType cost = 0)
: cost(cost), src(src), dst(dst) {}
auto operator<=>(const Edge& x) const = default;
};
} // namespace emthrm
#endif // EMTHRM_GRAPH_EDGE_HPP_
#line 1 "include/emthrm/graph/enumerate_bridges.hpp"
#line 6 "include/emthrm/graph/enumerate_bridges.hpp"
#line 1 "include/emthrm/graph/edge.hpp"
/**
* @title 辺
*/
#ifndef EMTHRM_GRAPH_EDGE_HPP_
#define EMTHRM_GRAPH_EDGE_HPP_
#include <compare>
namespace emthrm {
template <typename CostType>
struct Edge {
CostType cost;
int src, dst;
explicit Edge(const int src, const int dst, const CostType cost = 0)
: cost(cost), src(src), dst(dst) {}
auto operator<=>(const Edge& x) const = default;
};
} // namespace emthrm
#endif // EMTHRM_GRAPH_EDGE_HPP_
#line 8 "include/emthrm/graph/enumerate_bridges.hpp"
namespace emthrm {
template <typename CostType>
std::vector<Edge<CostType>> enumerate_bridges(
const std::vector<std::vector<Edge<CostType>>>& graph) {
const int n = graph.size();
std::vector<Edge<CostType>> res;
std::vector<int> depth(n, -1), imos(n, 0);
const auto dfs = [&graph, &res, &depth, &imos](
auto dfs, const int par, const int ver) -> void {
bool has_multiple_edges = false;
for (const Edge<CostType>& e : graph[ver]) {
if (depth[e.dst] == -1) {
depth[e.dst] = depth[ver] + 1;
dfs(dfs, ver, e.dst);
if (imos[e.dst] == 0) {
res.emplace_back(std::min(ver, e.dst), std::max(ver, e.dst), e.cost);
}
imos[ver] += imos[e.dst];
} else if (!has_multiple_edges && e.dst == par) {
has_multiple_edges = true;
} else if (depth[e.dst] < depth[ver]) {
++imos[ver];
--imos[e.dst];
}
}
};
for (int i = 0; i < n; ++i) {
if (depth[i] == -1) {
depth[i] = 0;
dfs(dfs, -1, i);
}
}
return res;
}
} // namespace emthrm
#line 14 "test/graph/enumerate_bridges.test.cpp"
int main() {
int v, e;
std::cin >> v >> e;
std::vector<std::vector<emthrm::Edge<bool>>> graph(v);
while (e--) {
int s, t;
std::cin >> s >> t;
graph[s].emplace_back(s, t);
graph[t].emplace_back(t, s);
}
std::vector<emthrm::Edge<bool>> bridges = emthrm::enumerate_bridges(graph);
std::ranges::sort(bridges.begin(), bridges.end(), {},
[](const emthrm::Edge<bool>& e) -> std::pair<int, int> {
return std::make_pair(e.src, e.dst);
});
for (const emthrm::Edge<bool>& bridge : bridges) {
std::cout << bridge.src << ' ' << bridge.dst << '\n';
}
return 0;
}