Boost C++ Libraries

libs/graph/example/kruskal-example.cpp

//=======================================================================
// Copyright 2001 Jeremy G. Siek, Andrew Lumsdaine, Lie-Quan Lee,
//
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//=======================================================================
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/kruskal_min_spanning_tree.hpp>
#include <iostream>
#include <fstream>

int main()
{
    using namespace boost;
    typedef adjacency_list< vecS, vecS, undirectedS, no_property,
        property< edge_weight_t, int > >
        Graph;
    typedef graph_traits< Graph >::edge_descriptor Edge;
    typedef std::pair< int, int > E;

    const int num_nodes = 5;
    E edge_array[] = { E(0, 2), E(1, 3), E(1, 4), E(2, 1), E(2, 3), E(3, 4),
        E(4, 0), E(4, 1) };
    int weights[] = { 1, 1, 2, 7, 3, 1, 1, 1 };
    std::size_t num_edges = sizeof(edge_array) / sizeof(E);
#if defined(BOOST_MSVC) && BOOST_MSVC <= 1300
    Graph g(num_nodes);
    property_map< Graph, edge_weight_t >::type weightmap = get(edge_weight, g);
    for (std::size_t j = 0; j < num_edges; ++j)
    {
        Edge e;
        bool inserted;
        boost::tie(e, inserted)
            = add_edge(edge_array[j].first, edge_array[j].second, g);
        weightmap[e] = weights[j];
    }
#else
    Graph g(edge_array, edge_array + num_edges, weights, num_nodes);
#endif
    property_map< Graph, edge_weight_t >::type weight = get(edge_weight, g);
    std::vector< Edge > spanning_tree;

    kruskal_minimum_spanning_tree(g, std::back_inserter(spanning_tree));

    std::cout << "Print the edges in the MST:" << std::endl;
    for (std::vector< Edge >::iterator ei = spanning_tree.begin();
         ei != spanning_tree.end(); ++ei)
    {
        std::cout << source(*ei, g) << " <--> " << target(*ei, g)
                  << " with weight of " << weight[*ei] << std::endl;
    }

    std::ofstream fout("figs/kruskal-eg.dot");
    fout << "graph A {\n"
         << " rankdir=LR\n"
         << " size=\"3,3\"\n"
         << " ratio=\"filled\"\n"
         << " edge[style=\"bold\"]\n"
         << " node[shape=\"circle\"]\n";
    graph_traits< Graph >::edge_iterator eiter, eiter_end;
    for (boost::tie(eiter, eiter_end) = edges(g); eiter != eiter_end; ++eiter)
    {
        fout << source(*eiter, g) << " -- " << target(*eiter, g);
        if (std::find(spanning_tree.begin(), spanning_tree.end(), *eiter)
            != spanning_tree.end())
            fout << "[color=\"black\", label=\"" << get(edge_weight, g, *eiter)
                 << "\"];\n";
        else
            fout << "[color=\"gray\", label=\"" << get(edge_weight, g, *eiter)
                 << "\"];\n";
    }
    fout << "}\n";
    return EXIT_SUCCESS;
}