Boost BGL BFS查找从源到目标的所有唯一路径 我使用Boost BGL C++,我需要图表来做一个从源顶点到目标顶点的BFS,并返回所有唯一的路径。
现在,我想到了一种使用过滤图获得包含源到目标路径的图子集的方法,但我意识到它基本上不是过滤的,因为过滤图包括访问的顶点,但不是源到目标路径的一部分。有没有办法获得这些信息,或者采用不同的方法更好 参考代码:Boost BGL BFS查找从源到目标的所有唯一路径 我使用Boost BGL C++,我需要图表来做一个从源顶点到目标顶点的BFS,并返回所有唯一的路径。,c++,boost,graph,C++,Boost,Graph,现在,我想到了一种使用过滤图获得包含源到目标路径的图子集的方法,但我意识到它基本上不是过滤的,因为过滤图包括访问的顶点,但不是源到目标路径的一部分。有没有办法获得这些信息,或者采用不同的方法更好 参考代码: boost::filtered_graph<DirectedGraph, boost::keep_all, std::function<bool(VertexDescr)>> Graph::getUniquePathsFromSource(VertexDescr so
boost::filtered_graph<DirectedGraph, boost::keep_all, std::function<bool(VertexDescr)>> Graph::getUniquePathsFromSource(VertexDescr source, VertexDescr target, DirectedGraph const & g)
{
std::vector<double> distances(num_vertices(g));
std::vector<boost::default_color_type> colormap(num_vertices(g));
// Run BFS and record all distances from the source node
breadth_first_search(g, source,
visitor(make_bfs_visitor(boost::record_distances(distances.data(), boost::on_tree_edge())))
.color_map(colormap.data())
);
for (auto vd : boost::make_iterator_range(vertices(g)))
if (colormap.at(vd) == boost::default_color_type{})
distances.at(vd) = -1;
distances[source] = -2;
boost::filtered_graph<DirectedGraph, boost::keep_all, std::function<bool(VertexDescr)>>
fg(g, {}, [&](VertexDescr vd) { return distances[vd] != -1; });
// Print edge list
std::cout << "filtered out-edges:" << std::endl;
std::cout << "Source Vertex: " << source << std::endl;
auto ei = boost::edges(fg);
typedef boost::property_map<DirectedGraph, boost::edge_weight_t>::type WeightMap;
WeightMap weights = get(boost::edge_weight, fg);
for (auto it = ei.first; it != ei.second; ++it)
{
if (source != boost::target(*it, g)) {
std::cout << "Edge Probability " << *it << ": " << get(weights, *it) << std::endl;
}
}
return fg;
}
输出(源=0,目标=5):
预期产出:
0->1->5
0->3->4->705->5
0->2->3->4->705->5
我不会使用BFS算法,因为它使用彩色贴图来跟踪访问的节点。但是,如果需要所有不同的路径,则不希望跳过已访问的节点(因为您可能会跳过其他路径) 相反,我将实现一个蛮力广度优先递归算法,它只访问所有相邻节点,除非它们已经在当前路径中 所需的所有状态都是当前路径 这里将更详细地解释这一想法:
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graph_utility.hpp> // print_graph
using namespace boost;
using Graph = adjacency_list<vecS, listS, directedS, property<vertex_index_t, int>, property<edge_weight_t, double> >;
Graph read_graph();
using Vertex = Graph::vertex_descriptor;
using Path = std::vector<Vertex>;
template <typename Report>
void all_paths_helper(Vertex from, Vertex to, Graph const& g, Path& path, Report const& callback) {
path.push_back(from);
if (from == to) {
callback(path);
} else {
for (auto out : make_iterator_range(out_edges(from, g))) {
auto v = target(out, g);
if (path.end() == std::find(path.begin(), path.end(), v)) {
all_paths_helper(v, to, g, path, callback);
}
}
}
path.pop_back();
}
template <typename Report>
void all_paths(Vertex from, Vertex to, Graph const& g, Report const& callback) {
Path state;
all_paths_helper(from, to, g, state, callback);
}
int main() {
auto g = read_graph();
print_graph(g, std::cout);
auto by_vertex_id = [&](int id) {
return *find_if(vertices(g), [&](Vertex vd) { return id == get(vertex_index, g, vd); });
};
all_paths(by_vertex_id(0), by_vertex_id(5), g, [&](Path const& path) {
std::cout << "Found path ";
for (auto v : path)
std::cout << get(vertex_index, g, v) << " ";
std::cout << "\n";
});
std::cout.flush();
}
// immaterial to the task, reading the graph
Graph read_graph() {
std::istringstream iss(R"(
0 1 0.001
0 2 0.1
0 3 0.001
1 5 0.001
2 3 0.001
3 4 0.1
1 482 0.1
482 635 0.001
4 705 0.1
705 5 0.1
1 1491 0.01
1 1727 0.01
1 1765 0.01)");
Graph g;
auto vertex = [&,idx=std::map<int,Vertex>{}](int id) mutable {
auto it = idx.find(id);
if (it != idx.end())
return it->second;
return idx.emplace(id, add_vertex(id, g)).first->second;
};
for (std::string line; getline(iss, line);) {
std::istringstream ls(line);
int s,t; double w;
if (ls >> s >> t >> w) {
add_edge(vertex(s), vertex(t), w, g);
} else {
std::cerr << "Skipped invalid line '" << line << "'\n";
}
}
return g;
}
+答案是1!我继续使用您的解决方案,没有使用
auto by_vertex_id=[&](int id){return*find_if(顶点(g),[&](顶点vd){return id==get(顶点索引,g,vd);}代码>据我所知,这检查顶点索引是否等于顶点描述符?您需要一些东西来找到源/目标顶点的描述符,对吗?如果你想更常规地拼写它(主要是,更少的lambda):甚至。C++确实有了长途跋涉,我明白了,我对lambda公约是比较新的,所以我仍然在学习它。谢谢
0->1->5
0->3->4->705->5
0->2->3->4->705->5
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graph_utility.hpp> // print_graph
using namespace boost;
using Graph = adjacency_list<vecS, listS, directedS, property<vertex_index_t, int>, property<edge_weight_t, double> >;
Graph read_graph();
using Vertex = Graph::vertex_descriptor;
using Path = std::vector<Vertex>;
template <typename Report>
void all_paths_helper(Vertex from, Vertex to, Graph const& g, Path& path, Report const& callback) {
path.push_back(from);
if (from == to) {
callback(path);
} else {
for (auto out : make_iterator_range(out_edges(from, g))) {
auto v = target(out, g);
if (path.end() == std::find(path.begin(), path.end(), v)) {
all_paths_helper(v, to, g, path, callback);
}
}
}
path.pop_back();
}
template <typename Report>
void all_paths(Vertex from, Vertex to, Graph const& g, Report const& callback) {
Path state;
all_paths_helper(from, to, g, state, callback);
}
int main() {
auto g = read_graph();
print_graph(g, std::cout);
auto by_vertex_id = [&](int id) {
return *find_if(vertices(g), [&](Vertex vd) { return id == get(vertex_index, g, vd); });
};
all_paths(by_vertex_id(0), by_vertex_id(5), g, [&](Path const& path) {
std::cout << "Found path ";
for (auto v : path)
std::cout << get(vertex_index, g, v) << " ";
std::cout << "\n";
});
std::cout.flush();
}
// immaterial to the task, reading the graph
Graph read_graph() {
std::istringstream iss(R"(
0 1 0.001
0 2 0.1
0 3 0.001
1 5 0.001
2 3 0.001
3 4 0.1
1 482 0.1
482 635 0.001
4 705 0.1
705 5 0.1
1 1491 0.01
1 1727 0.01
1 1765 0.01)");
Graph g;
auto vertex = [&,idx=std::map<int,Vertex>{}](int id) mutable {
auto it = idx.find(id);
if (it != idx.end())
return it->second;
return idx.emplace(id, add_vertex(id, g)).first->second;
};
for (std::string line; getline(iss, line);) {
std::istringstream ls(line);
int s,t; double w;
if (ls >> s >> t >> w) {
add_edge(vertex(s), vertex(t), w, g);
} else {
std::cerr << "Skipped invalid line '" << line << "'\n";
}
}
return g;
}
1 --> 5 482 1491 1727 1765
0 --> 1 2 3
2 --> 3
3 --> 4
5 -->
4 --> 705
482 --> 635
635 -->
705 --> 5
1491 -->
1727 -->
1765 -->
Found path 0 1 5
Found path 0 2 3 4 705 5
Found path 0 3 4 705 5