木の直径
(graph/tree-diameter.hpp)

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• Last update: 2021-08-01 23:46:19+09:00
• Include: #include "graph/tree-diameter.hpp"

Depends on

• graph/template.hpp

Verified with

• 木の直径のテスト (test/aoj/GRL_5_A.test.cpp)

Code

#ifndef __GRAPH__TREE_DIAMETER
#define __GRAPH__TREE_DIAMETER
// @title 木の直径

#include <utility>
#include "template.hpp"

namespace tree_diameter_
{
template< typename T >
std::pair< T, int > dfs(const Graph<T> &g, int idx, int par) {
  std::pair< T, int > ret(0, idx);
  for(auto &e : g[idx]) {
    if(e.to == par) continue;
    auto cost = dfs(g, e.to, idx);
    cost.first += e.cost;
    ret = max(ret, cost);
  }
  return ret;
}

} // namespace tree_diameter

template< typename T >
T tree_diameter(const Graph<T> &g) {
  auto p = tree_diameter_::dfs(g, 0, -1);
  auto q = tree_diameter_::dfs(g, p.second, -1);
  return (q.first);
}

#endif // __GRAPH__TREE_DIAMETER

#line 1 "graph/tree-diameter.hpp"


// @title 木の直径

#include <utility>
#line 1 "graph/template.hpp"



#include <iostream>
#include <vector>

template< typename T >
struct Edge {
  int from, to;
  T cost;
  Edge() {}
  Edge(int f, int t) : from(f), to(t), cost(1) {}
  Edge(int f, int t, T c) : from(f), to(t), cost(c) {}
  friend bool operator < (const Edge& lhs, const Edge& rhs) { return lhs.cost < rhs.cost; };
  friend bool operator > (const Edge& lhs, const Edge& rhs) { return rhs < lhs; };
  friend bool operator <= (const Edge& lhs, const Edge& rhs) { return !(lhs > rhs); };
  friend bool operator >= (const Edge& lhs, const Edge& rhs) { return !(lhs < rhs); };
};

template< typename T >
using Edges = std::vector< Edge< T > >;
template< typename T >
using Graph = std::vector< Edges< T > >;

template< typename T >
void debug(Graph<T> &g, int n = -1) {
    if (n == -1) n = g.size();
    for (int i = 0; i < n; ++i) {
        std::cerr << i  << "\t";
        for (auto &e: g[i]) {
            std::cerr << e.to << ",";
        }
        std::cerr << std::endl;
    }
}


#line 7 "graph/tree-diameter.hpp"

namespace tree_diameter_
{
template< typename T >
std::pair< T, int > dfs(const Graph<T> &g, int idx, int par) {
  std::pair< T, int > ret(0, idx);
  for(auto &e : g[idx]) {
    if(e.to == par) continue;
    auto cost = dfs(g, e.to, idx);
    cost.first += e.cost;
    ret = max(ret, cost);
  }
  return ret;
}

} // namespace tree_diameter

template< typename T >
T tree_diameter(const Graph<T> &g) {
  auto p = tree_diameter_::dfs(g, 0, -1);
  auto q = tree_diameter_::dfs(g, p.second, -1);
  return (q.first);
}

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