在breadth_first_search期间设置顶点的颜色

我想在BGL图上做区域生长。区域增长的思想是访问顶点，从指定的根顶点开始，收集并返回一个子图或一个顶点列表，这些顶点与它们的父顶点相比通过了一些标准函数。例如，假设我们有一个简单的图形，看起来像这样:

A-B-C-D

，边权为:

AB = 4，BC = 10，CD = 3

现在我们想从a开始生长一个区域，我们想做以下操作:

• 发现A并添加到连接区域
• 发现B，并决定B是否与a"足够相似"。在这个例子中，假设标准是边权值的阈值:如果边权值> 5，那么我们不应该继续遍行到B。所以这里，AB = 4，我们应该增长到B，但由于BC=10，我们应该永远不会到达C。
  • 如果是，将B添加到连接区域，并继续发现C并检查C是否与B足够相似，等等。
  • 如果没有，停止并返回当前连接的区域

我可以在来访者的tree_edge函数中查看这个准则函数。如果A和B太不相似，我试图通过将传递给tree_edge的边缘的目标顶点设置为黑色来"阻止"BFS继续(将B添加到队列中，然后稍后处理它等)。然而，这似乎并没有阻止遍历:

#include <iostream>
#include <boost/graph/graph_traits.hpp>
#include <boost/graph/adjacency_list.hpp>
#include <boost/property_map/property_map.hpp>
#include <boost/graph/breadth_first_search.hpp>
using EdgeWeightProperty = boost::property<boost::edge_weight_t, float>;
using ColorPropertyType = boost::property<boost::vertex_color_t, boost::default_color_type>;
using GraphType =  boost::adjacency_list<boost::setS, // out edge container
                                         boost::vecS, // vertex container
                                         boost::undirectedS, // directed or undirected
                                         ColorPropertyType, // vertex properites
                                         EdgeWeightProperty> // edge properties
                                         ;
template <typename TGraph>
void printColors(const TGraph& g)
{
    const auto& colorMapGraph = get(boost::vertex_color_t(), g);
    std::cout << "colors: ";
    for(unsigned int i = 0; i < num_vertices(g); ++i) {
        std::cout << get(colorMapGraph, vertex(i, g)) << " ";
    }
    std::cout << std::endl;
}
class BreadthFirstSearchVisitor : public boost::default_bfs_visitor
{
public:
    // We must provide a mutable version of the graph to the visitor since we want to change properties
    BreadthFirstSearchVisitor(GraphType& graph) : mGraph(graph) {}
    template < typename TEdge, typename TGraph>
    void tree_edge(TEdge e, const TGraph& g) const
    {
        std::cout << std::endl << "tree_edge: " << e << std::endl;
        printColors(g);
        const auto& colors = get(boost::vertex_color_t(), mGraph); // Though this is const&, you can still call put()
        const auto& edgeWeights = get(boost::edge_weight_t(), mGraph);
        boost::graph_traits<GraphType>::vertex_descriptor targetVertex = boost::target(e, g);
        std::cout << "targetVertex: " << targetVertex << std::endl;
        float edgeWeight = get(edgeWeights, e);
        std::cout << "edgeWeight: " << edgeWeight << std::endl;
        if(edgeWeight > 5.f) {
            std::cout << "Next vertex does not belong to the region!" << std::endl;
            put(colors, vertex(targetVertex, mGraph), boost::color_traits<GraphType>::black());
            printColors(g);
        }
    }
    // A very strange pattern, but this is (officially) recommended here: http://stackoverflow.com/a/2608616/284529
    GraphType& mGraph;
};
int main(int,char*[])
{
    // Create a graph object
    GraphType g(4);
    EdgeWeightProperty e0 = 4.f;
    add_edge(0, 1, e0, g);
    EdgeWeightProperty e1 = 10.f;
    add_edge(1, 2, e1, g);
    EdgeWeightProperty e2 = 3.f;
    add_edge(2, 3, e2, g);
    BreadthFirstSearchVisitor breadthFirstSearchVisitor(g);
    unsigned int startVertex = 0;
    // named argument signature
    breadth_first_search(g, vertex(startVertex, g), visitor(breadthFirstSearchVisitor).color_map(get(boost::vertex_color_t(), g)));
    return 0;
}

输出为:

tree_edge: (0,1)
colors: 1 0 0 0 
targetVertex: 1
edgeWeight: 4
tree_edge: (1,2)
colors: 4 1 0 0 
targetVertex: 2
edgeWeight: 10
Next vertex does not belong to the region!
colors: 4 1 4 0 
tree_edge: (2,3)
colors: 4 4 1 0 
targetVertex: 3
edgeWeight: 3

但是我希望它不会调用边缘为(2,3)的tree_edge因为我们将顶点2标记为黑色

谁能解释一下为什么这不能像我期望的那样工作?