#include <boost/config.hpp>
#include <iostream>
#include <boost/graph/graph_traits.hpp>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/dijkstra_shortest_paths.hpp>
using namespace boost;
// define visitor for discover_vertex event
template <class Vertex, class Tag>
struct target_visitor : public default_dijkstra_visitor
{
target_visitor(Vertex u) : v(u) { }
template <class Graph>
void examine_vertex(Vertex u, Graph& g)
{
if( u == v ) {
throw(-1);
}
}
private:
Vertex v;
};
template <class Vertex, class Tag>
target_visitor<Vertex, Tag>
target_visit(Vertex u, Tag) {
return target_visitor<Vertex, Tag>(u);
}
int main(int argc, char** argv)
{
typedef adjacency_list < listS, vecS, directedS,
no_property, property < edge_weight_t, int > > graph_t;
typedef graph_traits < graph_t >::vertex_descriptor vertex_descriptor;
typedef graph_traits < graph_t >::edge_descriptor edge_descriptor;
typedef std::pair<int, int> Edge;
const int num_nodes = 5;
enum nodes { A, B, C, D, E };
char name[] = "ABCDE";
Edge edge_array[] =
{
Edge(A, C), Edge(B, B), Edge(B, D), Edge(B, E),
Edge(C, B), Edge(C, D), Edge(D, E), Edge(E, A), Edge(E, B)
};
int weights[] = { 1, 2, 1, 2, 7, 3, 1, 1, 1 };
int num_arcs = sizeof(edge_array) / sizeof(Edge);
graph_t g(edge_array, edge_array + num_arcs, weights, num_nodes);
property_map<graph_t, edge_weight_t>::type weightmap = get(edge_weight, g);
std::vector<vertex_descriptor> p(num_vertices(g));
std::vector<int> d(num_vertices(g));
// choose source and target
vertex_descriptor src = vertex(A, g);
vertex_descriptor targ = vertex(C, g);
try {
dijkstra_shortest_paths(g, src,
predecessor_map(&p[0]).distance_map(&d[0]).visitor(target_visit(targ,
on_examine_vertex())));
}
catch( ... ) {
}
std::cout << "distances and parents:" << std::endl;
graph_traits < graph_t >::vertex_iterator vi, vend;
for (tie(vi, vend) = vertices(g); vi != vend; ++vi) {
std::cout << "distance(" << name[*vi] << ") = " << d[*vi] << ", ";
std::cout << "parent(" << name[*vi] << ") = " << name[p[*vi]] << std::endl;
}
system("PAUSE");
return EXIT_SUCCESS;
}
> Is there an easy/already implemented way to stop the computation of
> the dijkstra_shortest_path algorithm when some target vertex is marked
> as black??
The recommended method is to use a visitor that throws an exception when the
target is colored black.
Daniel
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