提升dijkstra弦边重量

时间:2016-01-19 13:31:39

标签: c++ c++11 boost dijkstra boost-graph

是否可以使用字符串值而不是双重属性 typedef adjacency_list < vecS, vecS, directedS, property<vertex_name_t, string>, property < edge_weight_t, string> > Graph; 我的目标是使用dijkstra算法。 PS:我已经尝试用字符串替换double,它会在算法中产生错误。

std::vector<vertexd> P(num_vertices(g));
std::vector<string> d(num_vertices(g));
vertexd s = vertex(0, g);

dijkstra_shortest_paths(g, s,
    predecessor_map(boost::make_iterator_property_map(P.begin(), get(boost::vertex_index, g))).
    distance_map(boost::make_iterator_property_map(d.begin(), get(boost::vertex_index, g))));

错误:

  

错误13错误C2664:'D boost :: closed_plus :: operator()(const T&amp;,const T&amp;)const':不能从'const std :: basic_string,std :: allocator&gt;转换参数2 “ 'const D&amp;' C:\ boost_1_58_0 \ boost \ graph \ dijkstra_shortest_paths.hpp 190

1 个答案:

答案 0 :(得分:2)

是的,你可以拥有一个字符串属性。

不,dijkstra要求

  

所有边权重为非负的情况下的加权,有向或无向图

所以重量必须是数字。当然,如果你可以为你的属性类型实现算术运算和std::numeric_limit<>,那么它可能没什么问题(但是在你这样做之前你真的要抓住它)。

更新 _实际上,事实证明这个文档有点简化,你实际上可以覆盖你的体重类型的零,比较和组合。请参阅注释中的linked sample(HT @cv_and_he)_

所以,我讨厌那个人,但是:为什么

因为权重是任何单位的金额,所以将它们存储为字符串的目标是什么?您是否可能有不同的问题阻止您正确存储权重?

那就是说,这是一种方式:

使用transform_value_property_map,你可以动态地将字符串转换为双打:

<强> Live On Coliru

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/dag_shortest_paths.hpp>
#include <boost/graph/graphviz.hpp>
#include <boost/property_map/transform_value_property_map.hpp>
#include <boost/lexical_cast.hpp>
#include <iostream>

using Weight = std::string;
//using Weight = double;

typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS,
        boost::property<boost::vertex_name_t, std::string>,
        boost::property<boost::edge_weight_t, Weight>
    > Graph;

using vertexd = Graph::vertex_descriptor;

Graph generate();

int main() {
    using namespace boost;

    Graph g = generate();
    std::vector<vertexd> P(num_vertices(g));
    std::vector<double>  d(num_vertices(g));
    vertexd s = vertex(0, g);

    auto to_double = [](Weight const& v) { return lexical_cast<double>(v); };

    dijkstra_shortest_paths(
        g, s, 
         weight_map  (make_transform_value_property_map(to_double, get(edge_weight, g)))
        .predecessor_map(make_container_vertex_map(P))
        .distance_map(make_container_vertex_map(d))
    );

    boost::dynamic_properties dp;
    dp.property("node_id", get(vertex_name, g));
    dp.property("label",  get(edge_weight, g));
    write_graphviz_dp(std::cout, g, dp);
}

#include <boost/graph/random.hpp>
#include <boost/range/iterator_range.hpp>
#include <random>

Graph generate() {
    using namespace boost;

    std::mt19937 prng { std::random_device {} () };
    Graph g;
    generate_random_graph(g, 10, 20, prng);

    for (auto v : make_iterator_range(vertices(g)))
        put(vertex_name, g, v, "vertex" + std::to_string(v));

#if 0
    // in case `Weight` is double
    auto gen_weight = [&, dist=std::uniform_real_distribution<Weight>(0,1)] () mutable -> Weight {
        return dist(prng);
    };
#else
    // in case `Weight` is std::string
    auto randchar = [&, dist=std::uniform_int_distribution<>('0','9')] () mutable -> char { return dist(prng); };

    auto gen_weight = [&] () {
        Weight tmp(3, ' ');
        std::generate(tmp.begin(), tmp.end(), randchar);
        return tmp;
    };
#endif

    for (auto e : make_iterator_range(edges(g)))
        put(edge_weight, g, e, gen_weight());

    return g;
}

输出随机生成的图形,例如:

digraph G {
    vertex0->vertex5  [label=503];
    vertex0->vertex8  [label=653];
    vertex0->vertex8  [label=931];
    vertex1->vertex6  [label=022];
    vertex1->vertex8  [label=536];
    vertex1->vertex5  [label=400];
    vertex1->vertex4  [label=056];
    vertex3->vertex8  [label=555];
    vertex4->vertex7  [label=052];
    vertex4->vertex6  [label=542];
    vertex4->vertex3  [label=024];
    vertex5->vertex7  [label=595];
    vertex5->vertex8  [label=850];
    vertex7->vertex4  [label=464];
    vertex7->vertex9  [label=484];
    vertex8->vertex0  [label=274];
    vertex8->vertex1  [label=131];
    vertex8->vertex6  [label=529];
    vertex9->vertex1  [label=239];
    vertex9->vertex3  [label=362];
}

呈现为

enter image description here