Boost C++ Libraries

libs/graph/example/stoer_wagner.cpp

//            Copyright Daniel Trebbien 2010.
// Distributed under the Boost Software License, Version 1.0.
//   (See accompanying file LICENSE_1_0.txt or the copy at
//         http://www.boost.org/LICENSE_1_0.txt)

#include <cassert>
#include <cstddef>
#include <cstdlib>
#include <iostream>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graph_traits.hpp>
#include <boost/graph/one_bit_color_map.hpp>
#include <boost/graph/stoer_wagner_min_cut.hpp>
#include <boost/property_map/property_map.hpp>
#include <boost/typeof/typeof.hpp>

struct edge_t
{
    unsigned long first;
    unsigned long second;
};

// A graphic of the min-cut is available at
// <http://www.boost.org/doc/libs/release/libs/graph/doc/stoer_wagner_imgs/stoer_wagner.cpp.gif>
int main()
{
    using namespace std;

    typedef boost::adjacency_list< boost::vecS, boost::vecS, boost::undirectedS,
        boost::no_property, boost::property< boost::edge_weight_t, int > >
        undirected_graph;
    typedef boost::property_map< undirected_graph, boost::edge_weight_t >::type
        weight_map_type;
    typedef boost::property_traits< weight_map_type >::value_type weight_type;

    // define the 16 edges of the graph. {3, 4} means an undirected edge between
    // vertices 3 and 4.
    edge_t edges[] = { { 3, 4 }, { 3, 6 }, { 3, 5 }, { 0, 4 }, { 0, 1 },
        { 0, 6 }, { 0, 7 }, { 0, 5 }, { 0, 2 }, { 4, 1 }, { 1, 6 }, { 1, 5 },
        { 6, 7 }, { 7, 5 }, { 5, 2 }, { 3, 4 } };

    // for each of the 16 edges, define the associated edge weight. ws[i] is the
    // weight for the edge that is described by edges[i].
    weight_type ws[] = { 0, 3, 1, 3, 1, 2, 6, 1, 8, 1, 1, 80, 2, 1, 1, 4 };

    // construct the graph object. 8 is the number of vertices, which are
    // numbered from 0 through 7, and 16 is the number of edges.
    undirected_graph g(edges, edges + 16, ws, 8, 16);

    // define a property map, `parities`, that will store a boolean value for
    // each vertex. Vertices that have the same parity after
    // `stoer_wagner_min_cut` runs are on the same side of the min-cut.
    BOOST_AUTO(parities,
        boost::make_one_bit_color_map(
            num_vertices(g), get(boost::vertex_index, g)));

    // run the Stoer-Wagner algorithm to obtain the min-cut weight. `parities`
    // is also filled in.
    int w = boost::stoer_wagner_min_cut(
        g, get(boost::edge_weight, g), boost::parity_map(parities));

    cout << "The min-cut weight of G is " << w << ".\n" << endl;
    assert(w == 7);

    cout << "One set of vertices consists of:" << endl;
    size_t i;
    for (i = 0; i < num_vertices(g); ++i)
    {
        if (get(parities, i))
            cout << i << endl;
    }
    cout << endl;

    cout << "The other set of vertices consists of:" << endl;
    for (i = 0; i < num_vertices(g); ++i)
    {
        if (!get(parities, i))
            cout << i << endl;
    }
    cout << endl;

    return EXIT_SUCCESS;
}