:warning: library/graph/LowLink.hpp

Depends on

Code

#include <numeric>
#include <ranges>
#include <utility>
#include <vector>

#include "library/graph/Graph.hpp"

class LowLink {
    Graph g;
    std::vector<int> ord, low_link;
    int cnt;

    static inline void chmin(int &a, int b) { a = std::min(a, b); }

    void dfs(int p, int v) {
        ord[v] = cnt++;
        for (int to : g[v])
            if (~ord[to]) {
                if (to != p)
                    chmin(low_link[v], to);
            } else {
                dfs(v, to);
                chmin(low_link[v], low_link[to]);
            }
    }

  public:
    LowLink(const Graph &g) : g(g), ord(g.n, -1), low_link(g.n), cnt(0) {
        std::iota(low_link.begin(), low_link.end(), 0);
        assert(g.is_prepared());
        for (int v = 0; v < g.n; v++)
            if (ord[v] < 0)
                dfs(-1, v);
    }

    int get_ord(int v) const { return ord[v]; }
    int get_low_link(int v) const { return low_link[v]; }
    bool is_bridge(int u, int v) const {
        if (ord[u] > ord[v])
            std::swap(u, v);
        return ord[u] < low_link[v];
    }
};
#line 1 "library/graph/LowLink.hpp"
#include <numeric>
#include <ranges>
#include <utility>
#include <vector>

#line 2 "library/graph/Graph.hpp"

#include <cassert>
#include <iostream>
#line 6 "library/graph/Graph.hpp"

struct Edge {
    int from, to;
    Edge() = default;
    Edge(int from, int to) : from(from), to(to) {}
    operator int() const { return to; }
};

struct Graph {
    int n;
    using edge_type = Edge;
    std::vector<edge_type> edges;

  protected:
    std::vector<int> in_deg;
    bool prepared;
    class OutgoingEdges {
        Graph *g;
        int l, r;

      public:
        OutgoingEdges(Graph *g, int l, int r) : g(g), l(l), r(r) {}
        edge_type *begin() { return &(g->edges[l]); }
        edge_type *end() { return &(g->edges[r]); }
        edge_type &operator[](int i) { return g->edges[l + i]; }
        int size() const { return r - l; }
    };
    class ConstOutgoingEdges {
        const Graph *g;
        int l, r;

      public:
        ConstOutgoingEdges(const Graph *g, int l, int r) : g(g), l(l), r(r) {}
        const edge_type *begin() const { return &(g->edges[l]); }
        const edge_type *end() const { return &(g->edges[r]); }
        const edge_type &operator[](int i) const { return g->edges[l + i]; }
        int size() const { return r - l; }
    };

  public:
    OutgoingEdges operator[](int v) {
        assert(prepared);
        return {this, in_deg[v], in_deg[v + 1]};
    }
    const ConstOutgoingEdges operator[](int v) const {
        assert(prepared);
        return {this, in_deg[v], in_deg[v + 1]};
    }

    bool is_prepared() const { return prepared; }

    Graph() : n(0), in_deg(1, 0), prepared(false) {}
    Graph(int n) : n(n), in_deg(n + 1, 0), prepared(false) {}
    Graph(int n, int m, bool directed = false, int indexed = 1)
        : n(n), in_deg(n + 1, 0), prepared(false) {
        scan(m, directed, indexed);
    }

    void resize(int n) { n = n; }

    void add_arc(int from, int to) {
        assert(!prepared);
        assert(0 <= from and from < n and 0 <= to and to < n);
        edges.emplace_back(from, to);
        in_deg[from + 1]++;
    }
    void add_edge(int u, int v) {
        add_arc(u, v);
        add_arc(v, u);
    }
    void add_arc(const edge_type &e) { add_arc(e.from, e.to); }
    void add_edge(const edge_type &e) { add_edge(e.from, e.to); }

    void scan(int m, bool directed = false, int indexed = 1) {
        edges.reserve(directed ? m : 2 * m);
        while (m--) {
            int u, v;
            std::cin >> u >> v;
            u -= indexed;
            v -= indexed;
            if (directed)
                add_arc(u, v);
            else
                add_edge(u, v);
        }
        build();
    }

    void build() {
        assert(!prepared);
        prepared = true;
        for (int v = 0; v < n; v++)
            in_deg[v + 1] += in_deg[v];
        std::vector<edge_type> new_edges(in_deg.back());
        auto counter = in_deg;
        for (auto &&e : edges)
            new_edges[counter[e.from]++] = e;
        edges = new_edges;
    }

    void graph_debug() const {
#ifndef __LOCAL
        return;
#endif
        assert(prepared);
        for (int from = 0; from < n; from++) {
            std::cerr << from << ";";
            for (int i = in_deg[from]; i < in_deg[from + 1]; i++)
                std::cerr << edges[i].to << " ";
            std::cerr << "\n";
        }
    }
};
#line 7 "library/graph/LowLink.hpp"

class LowLink {
    Graph g;
    std::vector<int> ord, low_link;
    int cnt;

    static inline void chmin(int &a, int b) { a = std::min(a, b); }

    void dfs(int p, int v) {
        ord[v] = cnt++;
        for (int to : g[v])
            if (~ord[to]) {
                if (to != p)
                    chmin(low_link[v], to);
            } else {
                dfs(v, to);
                chmin(low_link[v], low_link[to]);
            }
    }

  public:
    LowLink(const Graph &g) : g(g), ord(g.n, -1), low_link(g.n), cnt(0) {
        std::iota(low_link.begin(), low_link.end(), 0);
        assert(g.is_prepared());
        for (int v = 0; v < g.n; v++)
            if (ord[v] < 0)
                dfs(-1, v);
    }

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