权重映射作为 Boost Graph Dijkstra 算法中的函数

Question

我正在使用 Boost Graph Libraries 并且需要使用一个权重图，它不是常数，而是参数 K 的函数（即边成本取决于 K）。在实践中，给定以下代码：

#include <boost/config.hpp>
#include <iostream>
#include <fstream>
#include <boost/graph/graph_traits.hpp>
#include <boost/graph/dijkstra_shortest_paths.hpp>
#include <boost/graph/adjacency_list.hpp>

struct Edge {
        Edge(float weight_) : weight(weight_) {}
        float weight;
        float getWeight(int K)
        {
            return K*weight;
        }
};



int main(int, char**){
        typedef boost::adjacency_list < boost::vecS, boost::vecS, boost::directedS, boost::no_property, Edge > graph_t;
        typedef boost::graph_traits < graph_t >::vertex_descriptor vertex_t;
        graph_t g;
        vertex_t a = boost::add_vertex(g);
        vertex_t b = boost::add_vertex(g);
        vertex_t c = boost::add_vertex(g);
        vertex_t d = boost::add_vertex(g);
        boost::add_edge(a, b, Edge(3), g);
        boost::add_edge(b, c, Edge(3), g);
        boost::add_edge(a, d, Edge(1), g);
        boost::add_edge(d, c, Edge(4), g);

        std::vector<vertex_t> preds(4);

        // Traditional dijsktra (sum)
        boost::dijkstra_shortest_paths(g, a, boost::predecessor_map(&preds[0]).weight_map(boost::get(&Edge::weight,g)));

        return 0;
}

我想调用Dijkstra算法如下：

boost::dijkstra_shortest_paths(g, a, boost::predecessor_map(&preds[0]).weight_map(boost::get(&Edge::getWeight(2),g)));

但是报错如下

cannot call member function ‘float Edge::getWeight(int)’ without object

有人知道怎么解决吗？

Answer 1

有许多 属性 地图风格。特别是 transform_value_property_map 可以在这里使用。

简单方法 C++03

假设你写的是 c++03：

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#include <boost/property_map/transform_value_property_map.hpp>
#include <boost/bind.hpp>

// ...

boost::dijkstra_shortest_paths(g, a, boost::predecessor_map(&preds[0]).weight_map(
            boost::make_transform_value_property_map(
                boost::bind(&Edge::getWeight ,_1, 2), 
                boost::get(boost::edge_bundle, g))
        ));

更干净的 C++11

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auto wmap = make_transform_value_property_map([](Edge& e) { return e.getWeight(2); }, get(boost::edge_bundle, g));
boost::dijkstra_shortest_paths(g, a, boost::predecessor_map(&preds[0]).weight_map(wmap));

您可以删除 boost/bind.hpp 包含。

奖励：删除 getWeight() 成员函数

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你实际上并不需要它。您可以就地编写 Phoenix 演员：

#include <boost/phoenix.hpp>
using boost::phoenix::arg_names::arg1;

auto wmap = make_transform_value_property_map(2 * (&arg1->*&Edge::weight), get(boost::edge_bundle, g));

或者再次使用c++11:

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auto wmap = make_transform_value_property_map([](Edge& e) { return e.weight * 2; }, get(boost::edge_bundle, g));