test/aoj/GRL_3_B.test.cpp

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• Last update: 2025-02-21 23:59:41+09:00
• Problem: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=GRL_3_B

Depends on

• Lowlink (graph/lowlink.hpp)

Code

#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=GRL_3_B"

#include "../../graph/lowlink.hpp"

#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int V, E;
    cin >> V >> E;
    vector<vector<int>> G(V);
    for (int i = 0; i < E; ++i) {
        int s, t;
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }
    Lowlink lowlink(G);
    auto bridges = lowlink.bridge;
    sort(bridges.begin(), bridges.end());
    for (auto& p : bridges) {
        cout << p.first << " " << p.second << "\n";
    }
}

#line 1 "test/aoj/GRL_3_B.test.cpp"
#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=GRL_3_B"

#line 2 "graph/lowlink.hpp"
#include <algorithm>
#include <utility>
#include <vector>

class Lowlink {
   public:
    std::vector<int> ord, low;
    std::vector<std::pair<int, int>> bridge;
    std::vector<int> articulation;

    Lowlink() = default;
    explicit Lowlink(const std::vector<std::vector<int>>& G)
        : ord(G.size(), -1), low(G.size()), G(G) {
        for (int i = 0; i < (int)G.size(); ++i) {
            if (ord[i] == -1) dfs(i, -1);
        }
    }

    bool is_bridge(int u, int v) const {
        if (ord[u] > ord[v]) std::swap(u, v);
        return ord[u] < low[v];
    }

   private:
    std::vector<std::vector<int>> G;
    int k = 0;

    void dfs(int v, int p) {
        low[v] = ord[v] = k++;
        bool is_articulation = false, checked = false;
        int cnt = 0;
        for (int c : G[v]) {
            if (c == p && !checked) {
                checked = true;
                continue;
            }
            if (ord[c] == -1) {
                ++cnt;
                dfs(c, v);
                low[v] = std::min(low[v], low[c]);
                if (p != -1 && ord[v] <= low[c]) is_articulation = true;
                if (ord[v] < low[c]) bridge.push_back(std::minmax(v, c));
            } else {
                low[v] = std::min(low[v], ord[c]);
            }
        }
        if (p == -1 && cnt > 1) is_articulation = true;
        if (is_articulation) articulation.push_back(v);
    }
};
#line 4 "test/aoj/GRL_3_B.test.cpp"

#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int V, E;
    cin >> V >> E;
    vector<vector<int>> G(V);
    for (int i = 0; i < E; ++i) {
        int s, t;
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }
    Lowlink lowlink(G);
    auto bridges = lowlink.bridge;
    sort(bridges.begin(), bridges.end());
    for (auto& p : bridges) {
        cout << p.first << " " << p.second << "\n";
    }
}

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