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:question: Heavy-Light-Decomposition(HL分解)
(graph/tree/heavy-light-decomposition.hpp)

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#pragma once

#include "../graph-template.hpp"

/**
 * @brief Heavy-Light-Decomposition(HL分解)
 * @see https://smijake3.hatenablog.com/entry/2019/09/15/200200
 */
template< typename T = int >
struct HeavyLightDecomposition : Graph< T > {
public:
  using Graph< T >::Graph;
  using Graph< T >::g;
  vector< int > sz, in, out, head, rev, par, dep;

  void build() {
    sz.assign(g.size(), 0);
    in.assign(g.size(), 0);
    out.assign(g.size(), 0);
    head.assign(g.size(), 0);
    rev.assign(g.size(), 0);
    par.assign(g.size(), 0);
    dep.assign(g.size(), 0);
    dfs_sz(0, -1, 0);
    int t = 0;
    dfs_hld(0, -1, t);
  }

  /* k: 0-indexed */
  int la(int v, int k) {
    while(1) {
      int u = head[v];
      if(in[v] - k >= in[u]) return rev[in[v] - k];
      k -= in[v] - in[u] + 1;
      v = par[u];
    }
  }

  int lca(int u, int v) const {
    for(;; v = par[head[v]]) {
      if(in[u] > in[v]) swap(u, v);
      if(head[u] == head[v]) return u;
    }
  }

  int dist(int u, int v) const {
    return dep[u] + dep[v] - 2 * dep[lca(u, v)];
  }

  template< typename E, typename Q, typename F, typename S >
  E query(int u, int v, const E &ti, const Q &q, const F &f, const S &s, bool edge = false) {
    E l = ti, r = ti;
    for(;; v = par[head[v]]) {
      if(in[u] > in[v]) swap(u, v), swap(l, r);
      if(head[u] == head[v]) break;
      l = f(q(in[head[v]], in[v] + 1), l);
    }
    return s(f(q(in[u] + edge, in[v] + 1), l), r);
  }

  template< typename E, typename Q, typename F >
  E query(int u, int v, const E &ti, const Q &q, const F &f, bool edge = false) {
    return query(u, v, ti, q, f, f, edge);
  }

  template< typename Q >
  void add(int u, int v, const Q &q, bool edge = false) {
    for(;; v = par[head[v]]) {
      if(in[u] > in[v]) swap(u, v);
      if(head[u] == head[v]) break;
      q(in[head[v]], in[v] + 1);
    }
    q(in[u] + edge, in[v] + 1);
  }

  /* {parent, child} */
  vector< pair< int, int > > compress(vector< int > &remark) {
    auto cmp = [&](int a, int b) { return in[a] < in[b]; };
    sort(begin(remark), end(remark), cmp);
    remark.erase(unique(begin(remark), end(remark)), end(remark));
    int K = (int) remark.size();
    for(int k = 1; k < K; k++) remark.emplace_back(lca(remark[k - 1], remark[k]));
    sort(begin(remark), end(remark), cmp);
    remark.erase(unique(begin(remark), end(remark)), end(remark));
    vector< pair< int, int > > es;
    stack< int > st;
    for(auto &k : remark) {
      while(!st.empty() && out[st.top()] <= in[k]) st.pop();
      if(!st.empty()) es.emplace_back(st.top(), k);
      st.emplace(k);
    }
    return es;
  }

  explicit HeavyLightDecomposition(const Graph< T > &g) : Graph< T >(g) {}

private:
  void dfs_sz(int idx, int p, int d) {
    dep[idx] = d;
    par[idx] = p;
    sz[idx] = 1;
    if(g[idx].size() && g[idx][0] == p) swap(g[idx][0], g[idx].back());
    for(auto &to : g[idx]) {
      if(to == p) continue;
      dfs_sz(to, idx, d + 1);
      sz[idx] += sz[to];
      if(sz[g[idx][0]] < sz[to]) swap(g[idx][0], to);
    }
  }

  void dfs_hld(int idx, int p, int &times) {
    in[idx] = times++;
    rev[in[idx]] = idx;
    for(auto &to : g[idx]) {
      if(to == p) continue;
      head[to] = (g[idx][0] == to ? head[idx] : to);
      dfs_hld(to, idx, times);
    }
    out[idx] = times;
  }
};
#line 2 "graph/tree/heavy-light-decomposition.hpp"

#line 2 "graph/graph-template.hpp"

/**
 * @brief Graph Template(グラフテンプレート)
 */
template< typename T = int >
struct Edge {
  int from, to;
  T cost;
  int idx;

  Edge() = default;

  Edge(int from, int to, T cost = 1, int idx = -1) : from(from), to(to), cost(cost), idx(idx) {}

  operator int() const { return to; }
};

template< typename T = int >
struct Graph {
  vector< vector< Edge< T > > > g;
  int es;

  Graph() = default;

  explicit Graph(int n) : g(n), es(0) {}

  size_t size() const {
    return g.size();
  }

  void add_directed_edge(int from, int to, T cost = 1) {
    g[from].emplace_back(from, to, cost, es++);
  }

  void add_edge(int from, int to, T cost = 1) {
    g[from].emplace_back(from, to, cost, es);
    g[to].emplace_back(to, from, cost, es++);
  }

  void read(int M, int padding = -1, bool weighted = false, bool directed = false) {
    for(int i = 0; i < M; i++) {
      int a, b;
      cin >> a >> b;
      a += padding;
      b += padding;
      T c = T(1);
      if(weighted) cin >> c;
      if(directed) add_directed_edge(a, b, c);
      else add_edge(a, b, c);
    }
  }

  inline vector< Edge< T > > &operator[](const int &k) {
    return g[k];
  }

  inline const vector< Edge< T > > &operator[](const int &k) const {
    return g[k];
  }
};

template< typename T = int >
using Edges = vector< Edge< T > >;
#line 4 "graph/tree/heavy-light-decomposition.hpp"

/**
 * @brief Heavy-Light-Decomposition(HL分解)
 * @see https://smijake3.hatenablog.com/entry/2019/09/15/200200
 */
template< typename T = int >
struct HeavyLightDecomposition : Graph< T > {
public:
  using Graph< T >::Graph;
  using Graph< T >::g;
  vector< int > sz, in, out, head, rev, par, dep;

  void build() {
    sz.assign(g.size(), 0);
    in.assign(g.size(), 0);
    out.assign(g.size(), 0);
    head.assign(g.size(), 0);
    rev.assign(g.size(), 0);
    par.assign(g.size(), 0);
    dep.assign(g.size(), 0);
    dfs_sz(0, -1, 0);
    int t = 0;
    dfs_hld(0, -1, t);
  }

  /* k: 0-indexed */
  int la(int v, int k) {
    while(1) {
      int u = head[v];
      if(in[v] - k >= in[u]) return rev[in[v] - k];
      k -= in[v] - in[u] + 1;
      v = par[u];
    }
  }

  int lca(int u, int v) const {
    for(;; v = par[head[v]]) {
      if(in[u] > in[v]) swap(u, v);
      if(head[u] == head[v]) return u;
    }
  }

  int dist(int u, int v) const {
    return dep[u] + dep[v] - 2 * dep[lca(u, v)];
  }

  template< typename E, typename Q, typename F, typename S >
  E query(int u, int v, const E &ti, const Q &q, const F &f, const S &s, bool edge = false) {
    E l = ti, r = ti;
    for(;; v = par[head[v]]) {
      if(in[u] > in[v]) swap(u, v), swap(l, r);
      if(head[u] == head[v]) break;
      l = f(q(in[head[v]], in[v] + 1), l);
    }
    return s(f(q(in[u] + edge, in[v] + 1), l), r);
  }

  template< typename E, typename Q, typename F >
  E query(int u, int v, const E &ti, const Q &q, const F &f, bool edge = false) {
    return query(u, v, ti, q, f, f, edge);
  }

  template< typename Q >
  void add(int u, int v, const Q &q, bool edge = false) {
    for(;; v = par[head[v]]) {
      if(in[u] > in[v]) swap(u, v);
      if(head[u] == head[v]) break;
      q(in[head[v]], in[v] + 1);
    }
    q(in[u] + edge, in[v] + 1);
  }

  /* {parent, child} */
  vector< pair< int, int > > compress(vector< int > &remark) {
    auto cmp = [&](int a, int b) { return in[a] < in[b]; };
    sort(begin(remark), end(remark), cmp);
    remark.erase(unique(begin(remark), end(remark)), end(remark));
    int K = (int) remark.size();
    for(int k = 1; k < K; k++) remark.emplace_back(lca(remark[k - 1], remark[k]));
    sort(begin(remark), end(remark), cmp);
    remark.erase(unique(begin(remark), end(remark)), end(remark));
    vector< pair< int, int > > es;
    stack< int > st;
    for(auto &k : remark) {
      while(!st.empty() && out[st.top()] <= in[k]) st.pop();
      if(!st.empty()) es.emplace_back(st.top(), k);
      st.emplace(k);
    }
    return es;
  }

  explicit HeavyLightDecomposition(const Graph< T > &g) : Graph< T >(g) {}

private:
  void dfs_sz(int idx, int p, int d) {
    dep[idx] = d;
    par[idx] = p;
    sz[idx] = 1;
    if(g[idx].size() && g[idx][0] == p) swap(g[idx][0], g[idx].back());
    for(auto &to : g[idx]) {
      if(to == p) continue;
      dfs_sz(to, idx, d + 1);
      sz[idx] += sz[to];
      if(sz[g[idx][0]] < sz[to]) swap(g[idx][0], to);
    }
  }

  void dfs_hld(int idx, int p, int &times) {
    in[idx] = times++;
    rev[in[idx]] = idx;
    for(auto &to : g[idx]) {
      if(to == p) continue;
      head[to] = (g[idx][0] == to ? head[idx] : to);
      dfs_hld(to, idx, times);
    }
    out[idx] = times;
  }
};
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