Centroid Decomposition
(tree/centroid-decomposition.hpp)

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• Last update: 2026-06-08 17:59:24+09:00
• Include: #include "tree/centroid-decomposition.hpp"

重心分解

概要

TODO

使い方

Required by

• 頂点間の距離の度数分布 (tree/frequency-table-of-tree-distance.hpp)

Verified with

• verify/verify-yosupo-graph/yosupo-frequency-table-of-tree-distance.test.cpp

Code

#pragma once



template <typename G>
struct CentroidDecomposition {
  const G &g;
  vector<int> sub;
  vector<bool> v;
  vector<vector<int>> tree;
  int root;

  CentroidDecomposition(const G &g_, int isbuild = true) : g(g_) {
    sub.resize(g.size(), 0);
    v.resize(g.size(), false);
    if (isbuild) build();
  }

  void build() {
    tree.resize(g.size());
    root = build_dfs(0);
  }

  int get_size(int cur, int par) {
    sub[cur] = 1;
    for (auto &dst : g[cur]) {
      if (dst == par || v[dst]) continue;
      sub[cur] += get_size(dst, cur);
    }
    return sub[cur];
  }

  int get_centroid(int cur, int par, int mid) {
    for (auto &dst : g[cur]) {
      if (dst == par || v[dst]) continue;
      if (sub[dst] > mid) return get_centroid(dst, cur, mid);
    }
    return cur;
  }

  int build_dfs(int cur) {
    int centroid = get_centroid(cur, -1, get_size(cur, -1) / 2);
    v[centroid] = true;
    for (auto &dst : g[centroid]) {
      if (!v[dst]) {
        int nxt = build_dfs(dst);
        if (centroid != nxt) tree[centroid].emplace_back(nxt);
      }
    }
    v[centroid] = false;
    return centroid;
  }
};

/**
 * @brief Centroid Decomposition
 */

#line 2 "tree/centroid-decomposition.hpp"



template <typename G>
struct CentroidDecomposition {
  const G &g;
  vector<int> sub;
  vector<bool> v;
  vector<vector<int>> tree;
  int root;

  CentroidDecomposition(const G &g_, int isbuild = true) : g(g_) {
    sub.resize(g.size(), 0);
    v.resize(g.size(), false);
    if (isbuild) build();
  }

  void build() {
    tree.resize(g.size());
    root = build_dfs(0);
  }

  int get_size(int cur, int par) {
    sub[cur] = 1;
    for (auto &dst : g[cur]) {
      if (dst == par || v[dst]) continue;
      sub[cur] += get_size(dst, cur);
    }
    return sub[cur];
  }

  int get_centroid(int cur, int par, int mid) {
    for (auto &dst : g[cur]) {
      if (dst == par || v[dst]) continue;
      if (sub[dst] > mid) return get_centroid(dst, cur, mid);
    }
    return cur;
  }

  int build_dfs(int cur) {
    int centroid = get_centroid(cur, -1, get_size(cur, -1) / 2);
    v[centroid] = true;
    for (auto &dst : g[centroid]) {
      if (!v[dst]) {
        int nxt = build_dfs(dst);
        if (centroid != nxt) tree[centroid].emplace_back(nxt);
      }
    }
    v[centroid] = false;
    return centroid;
  }
};

/**
 * @brief Centroid Decomposition
 */

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