test/graph/bridges.test.cpp

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Last update: 2026-01-09 14:45:55+09:00
Problem: https://onlinejudge.u-aizu.ac.jp/problems/GRL_3_B

Depends on

Bridges (graph/bridges.hpp)

Code

#define PROBLEM "https://onlinejudge.u-aizu.ac.jp/problems/GRL_3_B"

#include "graph/bridges.hpp"
#include <bits/stdc++.h>

int main() {
    std::cin.tie(0)->sync_with_stdio(0);
    int n, m;
    std::cin >> n >> m;
    std::vector<std::vector<int>> g(n);
    for (auto i = 0; i < m; ++i) {
        int u, v;
        std::cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    auto bridges = find_bridges(g);
    for (auto &[u, v] : bridges) {
        if (u > v) {
            std::swap(u, v);
        }
    }
    std::ranges::sort(bridges);
    for (auto [u, v] : bridges) {
        std::cout << u << ' ' << v << '\n';
    }
}

#line 1 "test/graph/bridges.test.cpp"
#define PROBLEM "https://onlinejudge.u-aizu.ac.jp/problems/GRL_3_B"

#line 1 "graph/bridges.hpp"



#include <algorithm>
#include <utility>
#include <vector>

std::vector<std::pair<int, int>> find_bridges(const auto &g) {
    auto n = (int)g.size();
    auto timer = 0;
    std::vector<int> visited(n, false), tin(n, -1), low(n, -1);
    std::vector<std::pair<int, int>> bridges;
    auto dfs = [&](auto self, int u, int p) -> void {
        visited[u] = true;
        tin[u] = low[u] = timer++;
        bool parent_skipped = false;
        for (auto v : g[u]) {
            if (v == p && !parent_skipped) {
                parent_skipped = true;
                continue;
            }
            if (visited[v]) {
                low[u] = std::min(low[u], tin[v]);
            } else {
                self(self, v, u);
                low[u] = std::min(low[u], low[v]);
                if (tin[u] < low[v]) {
                    bridges.emplace_back(u, v);
                }
            }
        }
    };
    for (auto i = 0; i < n; ++i) {
        if (!visited[i]) {
            dfs(dfs, i, -1);
        }
    }
    return bridges;
}


#line 4 "test/graph/bridges.test.cpp"
#include <bits/stdc++.h>

int main() {
    std::cin.tie(0)->sync_with_stdio(0);
    int n, m;
    std::cin >> n >> m;
    std::vector<std::vector<int>> g(n);
    for (auto i = 0; i < m; ++i) {
        int u, v;
        std::cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    auto bridges = find_bridges(g);
    for (auto &[u, v] : bridges) {
        if (u > v) {
            std::swap(u, v);
        }
    }
    std::ranges::sort(bridges);
    for (auto [u, v] : bridges) {
        std::cout << u << ' ' << v << '\n';
    }
}