rcpl

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:heavy_check_mark: verify/aoj_grl/aoj_grl_3_b.test.cpp

Depends on

Code

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

#include <bits/stdc++.h>

#include "graph/read_graph.hpp"
#include "graph/low_link.hpp"

int main() {
    int N, M;
    std::cin >> N >> M;
    auto G = read_graph<int>(N, M, 0, 0, 0);
    LowLink llink(G);
    auto ans = llink.bridges;
    std::sort(ans.begin(), ans.end());
    for (auto& [s, t] : ans) std::cout << s << ' ' << t << '\n';
    return 0;
}
#line 1 "verify/aoj_grl/aoj_grl_3_b.test.cpp"
#define PROBLEM "https://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=GRL_3_B"

#include <bits/stdc++.h>

#line 2 "graph/read_graph.hpp"

#line 2 "graph/graph_template.hpp"

#line 4 "graph/graph_template.hpp"
template <class T> struct Edge {
    int from, to;
    T cost;
    int id;

    Edge() = default;
    Edge(int from, int to, T cost = 1, int id = -1) : from(from), to(to), cost(cost), id(id) {}

    friend std::ostream &operator<<(std::ostream &os, const Edge<T> &e) {
        // output format: "{ id : from -> to, cost }"
        return os << "{ " << e.id << " : " << e.from << " -> " << e.to << ", " << e.cost << " }";
    }
};

template <class T> using Edges = std::vector<Edge<T>>;
template <class T> using Graph = std::vector<std::vector<Edge<T>>>;
#line 4 "graph/read_graph.hpp"

template <class T> Graph<T> read_graph(const int n, const int m, const bool weight = false, const bool directed = false, const int offset = 1) {
    Graph<T> g(n);
    for (int i = 0; i < m; i++) {
        int a, b;
        std::cin >> a >> b;
        a -= offset, b -= offset;
        if (weight) {
            T c;
            std::cin >> c;
            if (!directed) g[b].push_back(Edge(b, a, c, i));
            g[a].push_back(Edge(a, b, c, i));
        } else {
            // c = 1
            if (!directed) g[b].push_back(Edge(b, a, T(1), i));
            g[a].push_back(Edge(a, b, T(1), i));
        }
    }
    return g;
}

template <class T> Graph<T> read_parent(const int n, const bool weight = false, const bool directed = false, const int offset = 1) {
    Graph<T> g(n);
    for (int i = 1; i < n; i++) {
        int p;
        std::cin >> p;
        p -= offset;
        if (weight) {
            T c;
            std::cin >> c;
            if (!directed) g[i].push_back(Edge(i, p, c, i - 1));
            g[p].push_back(Edge(p, i, c, i - 1));
        } else {
            // c = 1
            if (!directed) g[i].push_back(Edge(i, p, T(1), i - 1));
            g[p].push_back(Edge(p, i, T(1), i - 1));
        }
    }
    return g;
}

std::tuple<Graph<int>, std::vector<std::vector<int>>, std::vector<std::pair<int, int>>> read_grid(const int h, const int w, std::string rel = ".#") {
    std::vector<std::string> s(h);
    std::vector id(h, std::vector<int>(w, -1));
    std::vector<std::pair<int, int>> loc;
    int n = 0;
    for (int i = 0; i < h; i++) {
        std::cin >> s[i];
        for (int j = 0; j < w; j++) {
            if (s[i][j] == rel[1]) {
                id[i][j] = n++;
                loc.emplace_back(i, j);
            }
        }
    }
    int m = 0;
    Graph<int> g(n);
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            if (s[i][j] == rel[1]) {
                if (i + 1 < h and s[i + 1][j] == rel[1]) {
                    g[id[i][j]].push_back(Edge(id[i][j], id[i + 1][j], 1, m));
                    g[id[i + 1][j]].push_back(Edge(id[i + 1][j], id[i][j], 1, m++));
                }
                if (j + 1 < w and s[i][j + 1] == rel[1]) {
                    g[id[i][j]].push_back(Edge(id[i][j], id[i][j + 1], 1, m));
                    g[id[i][j + 1]].push_back(Edge(id[i][j + 1], id[i][j], 1, m++));
                }
            }
        }
    }
    return {g, id, loc};
}
#line 2 "graph/low_link.hpp"

#line 4 "graph/low_link.hpp"

template <class T> struct LowLink {
    int n;
    std::vector<int> ord, low;
    std::vector<int> articulations;
    std::vector<int> roots;
    std::vector<std::pair<int, int>> bridges;  // edges {u, v} (u < v)
    std::vector<std::vector<int>> dfs_tree;

    LowLink(const Graph<T>& g) : n(int(g.size())) {
        ord.assign(n, -1);
        low.assign(n, -1);
        dfs_tree.resize(n);
        int ord_id = 0;
        auto dfs = [&](auto f, int cur, int par) -> void {
            low[cur] = ord[cur] = ord_id++;
            bool is_articulation = false;
            for (auto& e : g[cur]) {
                if (ord[e.to] == -1) {
                    // DFS 木上の辺に対する処理
                    f(f, e.to, cur);
                    dfs_tree[cur].push_back(e.to);
                    // e が DFS 木に含まれているので後退辺をすでに通った low[e.to] を使って更新して良い
                    low[cur] = std::min(low[cur], low[e.to]);
                    is_articulation |= (par != -1) and (ord[cur] <= low[e.to]);
                    if (ord[cur] < low[e.to]) {
                        bridges.emplace_back(std::minmax(cur, e.to));
                    }
                } else if (e.to != par) {
                    // 後退辺に対する処理
                    // Todo: multiple edges
                    low[cur] = std::min(low[cur], ord[e.to]);
                }
            }
            is_articulation |= par == -1 and int(dfs_tree[cur].size()) > 1;
            if (is_articulation) articulations.push_back(cur);
            return;
        };
        for (int i = 0; i < n; i++) {
            if (ord[i] == -1) {
                roots.push_back(i);
                dfs(dfs, i, -1);
            }
        }
    }
    // 連結成分数
    int count_components() { return int(roots.size()); }
    // 頂点 x を取り除くともともと 1 つだった連結成分がいくつになるか
    int count_components_remove(int x) {
        if (std::binary_search(roots.begin(), roots.end(), x)) {
            int c = int(dfs_tree[x].size());
            return c;
        } else {
            int c = 0;
            for (auto& e : dfs_tree[x]) {
                if (ord[x] <= low[e]) c++;
            }
            // 親の分で +1
            return c + 1;
        }
    }
};
#line 7 "verify/aoj_grl/aoj_grl_3_b.test.cpp"

int main() {
    int N, M;
    std::cin >> N >> M;
    auto G = read_graph<int>(N, M, 0, 0, 0);
    LowLink llink(G);
    auto ans = llink.bridges;
    std::sort(ans.begin(), ans.end());
    for (auto& [s, t] : ans) std::cout << s << ' ' << t << '\n';
    return 0;
}
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