BFS(幅優先探索) (graph/shortest-path/bfs.hpp)

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• Last update: 2024-05-01 23:44:47+09:00
• Include: #include "graph/shortest-path/bfs.hpp"

Depends on

• Graph Template(グラフテンプレート) (graph/graph-template.hpp)

Verified with

• test/verify/aoj-alds-1-11-c.test.cpp

Code

#pragma once

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

/**
 * @brief BFS(幅優先探索)
 */
template <typename T>
vector<T> bfs(const Graph<T> &g, int s) {
  T max_cost = 0, beet = 0;
  for (auto &es : g.g) {
    for (auto &e : es) max_cost = max(max_cost, e.cost);
  }
  ++max_cost;
  const auto INF = numeric_limits<T>::max();
  vector<T> dist(g.size(), INF);
  vector<queue<int> > ques(max_cost + 1);
  dist[s] = 0;
  ques[0].emplace(s);
  for (T cost = 0; cost <= beet; cost++) {
    auto &que = ques[cost % max_cost];
    while (!que.empty()) {
      int idx = que.front();
      que.pop();
      if (dist[idx] < cost) continue;
      for (auto &e : g[idx]) {
        auto next_cost = cost + e.cost;
        if (dist[e.to] <= next_cost) continue;
        ;
        dist[e.to] = next_cost;
        beet = max(beet, dist[e.to]);
        ques[dist[e.to] % max_cost].emplace(e.to);
      }
    }
  }
  return dist;
}

#line 2 "graph/shortest-path/bfs.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/shortest-path/bfs.hpp"

/**
 * @brief BFS(幅優先探索)
 */
template <typename T>
vector<T> bfs(const Graph<T> &g, int s) {
  T max_cost = 0, beet = 0;
  for (auto &es : g.g) {
    for (auto &e : es) max_cost = max(max_cost, e.cost);
  }
  ++max_cost;
  const auto INF = numeric_limits<T>::max();
  vector<T> dist(g.size(), INF);
  vector<queue<int> > ques(max_cost + 1);
  dist[s] = 0;
  ques[0].emplace(s);
  for (T cost = 0; cost <= beet; cost++) {
    auto &que = ques[cost % max_cost];
    while (!que.empty()) {
      int idx = que.front();
      que.pop();
      if (dist[idx] < cost) continue;
      for (auto &e : g[idx]) {
        auto next_cost = cost + e.cost;
        if (dist[e.to] <= next_cost) continue;
        ;
        dist[e.to] = next_cost;
        beet = max(beet, dist[e.to]);
        ques[dist[e.to] % max_cost].emplace(e.to);
      }
    }
  }
  return dist;
}

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