Graph/centroid_decomposition.hpp

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• Last update: 2020-11-05 12:15:41+09:00
• Include: #include "Graph/centroid_decomposition.hpp"

Depends on

• Graph/graph.hpp

Verified with

• Verify/centroid_decomposition_diameter.test.cpp

Code

#pragma once

#include "../Graph/graph.hpp"

template <class Cost = int>
struct Centroid {
    Graph<Cost> graph;
    std::vector<bool> deleted;
    std::vector<int> sz;

    explicit Centroid(const Graph<Cost>& graph)
        : graph(graph), deleted(graph.size(), false), sz(graph.size()) {}

    int szdfs(int v, int p = -1) {
        sz[v] = 1;
        for (auto e : graph[v]) {
            if (e.dst == p || deleted[e.dst]) continue;
            sz[v] += szdfs(e.dst, v);
        }
        return sz[v];
    }

    int find(int v) {
        int n = szdfs(v);

        int p = -1;
        while (true) {
            int nxt = -1;
            for (auto e : graph[v]) {
                if (e.dst == p || deleted[e.dst]) continue;
                if (nxt == -1 || sz[e.dst] > sz[nxt]) nxt = e.dst;
            }

            if (nxt == -1 || sz[nxt] <= n / 2) return v;
            p = v;
            v = nxt;
        }
    }
};

#line 2 "Graph/centroid_decomposition.hpp"

#line 2 "Graph/graph.hpp"

#include <vector>

template <class Cost = int>
struct Edge {
    int src, dst;
    Cost cost;

    Edge() = default;
    Edge(int src, int dst, Cost cost = 1)
        : src(src), dst(dst), cost(cost){};

    bool operator<(const Edge<Cost>& e) const { return cost < e.cost; }
    bool operator>(const Edge<Cost>& e) const { return cost > e.cost; }
};

template <class Cost = int>
struct Graph : public std::vector<std::vector<Edge<Cost>>> {
    using std::vector<std::vector<Edge<Cost>>>::vector;

    void span(bool direct, int src, int dst, Cost cost = 1) {
        (*this)[src].emplace_back(src, dst, cost);
        if (!direct) (*this)[dst].emplace_back(dst, src, cost);
    }
};
#line 4 "Graph/centroid_decomposition.hpp"

template <class Cost = int>
struct Centroid {
    Graph<Cost> graph;
    std::vector<bool> deleted;
    std::vector<int> sz;

    explicit Centroid(const Graph<Cost>& graph)
        : graph(graph), deleted(graph.size(), false), sz(graph.size()) {}

    int szdfs(int v, int p = -1) {
        sz[v] = 1;
        for (auto e : graph[v]) {
            if (e.dst == p || deleted[e.dst]) continue;
            sz[v] += szdfs(e.dst, v);
        }
        return sz[v];
    }

    int find(int v) {
        int n = szdfs(v);

        int p = -1;
        while (true) {
            int nxt = -1;
            for (auto e : graph[v]) {
                if (e.dst == p || deleted[e.dst]) continue;
                if (nxt == -1 || sz[e.dst] > sz[nxt]) nxt = e.dst;
            }

            if (nxt == -1 || sz[nxt] <= n / 2) return v;
            p = v;
            v = nxt;
        }
    }
};

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