Boost C++ Libraries

libs/graph/example/bellman-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/config.hpp>
#include <vector>
#include <iostream>
#include <fstream>
#include <iomanip>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/bellman_ford_shortest_paths.hpp>

using namespace boost;

template < typename Graph, typename ParentMap > struct edge_writer
{
    edge_writer(const Graph& g, const ParentMap& p) : m_g(g), m_parent(p) {}

    template < typename Edge >
    void operator()(std::ostream& out, const Edge& e) const
    {
        out << "[label=\"" << get(edge_weight, m_g, e) << "\"";
        typename graph_traits< Graph >::vertex_descriptor u = source(e, m_g),
                                                          v = target(e, m_g);
        if (m_parent[v] == u)
            out << ", color=\"black\"";
        else
            out << ", color=\"grey\"";
        out << "]";
    }
    const Graph& m_g;
    ParentMap m_parent;
};
template < typename Graph, typename Parent >
edge_writer< Graph, Parent > make_edge_writer(const Graph& g, const Parent& p)
{
    return edge_writer< Graph, Parent >(g, p);
}

struct EdgeProperties
{
    int weight;
};

int main()
{
    enum
    {
        u,
        v,
        x,
        y,
        z,
        N
    };
    char name[] = { 'u', 'v', 'x', 'y', 'z' };
    typedef std::pair< int, int > E;
    const int n_edges = 10;
    E edge_array[] = { E(u, y), E(u, x), E(u, v), E(v, u), E(x, y), E(x, v),
        E(y, v), E(y, z), E(z, u), E(z, x) };
    int weight[n_edges] = { -4, 8, 5, -2, 9, -3, 7, 2, 6, 7 };

    typedef adjacency_list< vecS, vecS, directedS, no_property, EdgeProperties >
        Graph;
#if defined(BOOST_MSVC) && BOOST_MSVC <= 1300
    // VC++ can't handle the iterator constructor
    Graph g(N);
    for (std::size_t j = 0; j < n_edges; ++j)
        add_edge(edge_array[j].first, edge_array[j].second, g);
#else
    Graph g(edge_array, edge_array + n_edges, N);
#endif
    graph_traits< Graph >::edge_iterator ei, ei_end;
    property_map< Graph, int EdgeProperties::* >::type weight_pmap
        = get(&EdgeProperties::weight, g);
    int i = 0;
    for (boost::tie(ei, ei_end) = edges(g); ei != ei_end; ++ei, ++i)
        weight_pmap[*ei] = weight[i];

    std::vector< int > distance(N, (std::numeric_limits< short >::max)());
    std::vector< std::size_t > parent(N);
    for (i = 0; i < N; ++i)
        parent[i] = i;
    distance[z] = 0;

#if defined(BOOST_MSVC) && BOOST_MSVC <= 1300
    bool r = bellman_ford_shortest_paths(g, int(N), weight_pmap, &parent[0],
        &distance[0], closed_plus< int >(), std::less< int >(),
        default_bellman_visitor());
#else
    bool r = bellman_ford_shortest_paths(g, int(N),
        weight_map(weight_pmap)
            .distance_map(&distance[0])
            .predecessor_map(&parent[0]));
#endif

    if (r)
        for (i = 0; i < N; ++i)
            std::cout << name[i] << ": " << std::setw(3) << distance[i] << " "
                      << name[parent[i]] << std::endl;
    else
        std::cout << "negative cycle" << std::endl;

    std::ofstream dot_file("figs/bellman-eg.dot");
    dot_file << "digraph D {\n"
             << "  rankdir=LR\n"
             << "  size=\"5,3\"\n"
             << "  ratio=\"fill\"\n"
             << "  edge[style=\"bold\"]\n"
             << "  node[shape=\"circle\"]\n";

    {
        for (boost::tie(ei, ei_end) = edges(g); ei != ei_end; ++ei)
        {
            graph_traits< Graph >::edge_descriptor e = *ei;
            graph_traits< Graph >::vertex_descriptor u = source(e, g),
                                                     v = target(e, g);
            // VC++ doesn't like the 3-argument get function, so here
            // we workaround by using 2-nested get()'s.
            dot_file << name[u] << " -> " << name[v] << "[label=\""
                     << get(get(&EdgeProperties::weight, g), e) << "\"";
            if (parent[v] == u)
                dot_file << ", color=\"black\"";
            else
                dot_file << ", color=\"grey\"";
            dot_file << "]";
        }
    }
    dot_file << "}";
    return EXIT_SUCCESS;
}