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Filename : dag_shortest_paths.hpp
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//=======================================================================
// Copyright 2002 Indiana University.
// Authors: Andrew Lumsdaine, Lie-Quan Lee, Jeremy G. Siek
//
// 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)
//=======================================================================

#ifndef BOOST_GRAPH_DAG_SHORTEST_PATHS_HPP
#define BOOST_GRAPH_DAG_SHORTEST_PATHS_HPP

#include <boost/graph/topological_sort.hpp>
#include <boost/graph/dijkstra_shortest_paths.hpp>

// single-source shortest paths for a Directed Acyclic Graph (DAG)

namespace boost
{

// Initalize distances and call depth first search
template < class VertexListGraph, class DijkstraVisitor, class DistanceMap,
    class WeightMap, class ColorMap, class PredecessorMap, class Compare,
    class Combine, class DistInf, class DistZero >
inline void dag_shortest_paths(const VertexListGraph& g,
    typename graph_traits< VertexListGraph >::vertex_descriptor s,
    DistanceMap distance, WeightMap weight, ColorMap color, PredecessorMap pred,
    DijkstraVisitor vis, Compare compare, Combine combine, DistInf inf,
    DistZero zero)
{
    typedef typename graph_traits< VertexListGraph >::vertex_descriptor Vertex;
    std::vector< Vertex > rev_topo_order;
    rev_topo_order.reserve(num_vertices(g));

    // Call 'depth_first_visit', not 'topological_sort', because we don't
    // want to traverse the entire graph, only vertices reachable from 's',
    // and 'topological_sort' will traverse everything. The logic below
    // is the same as for 'topological_sort', only we call 'depth_first_visit'
    // and 'topological_sort' calls 'depth_first_search'.
    topo_sort_visitor< std::back_insert_iterator< std::vector< Vertex > > >
        topo_visitor(std::back_inserter(rev_topo_order));
    depth_first_visit(g, s, topo_visitor, color);

    typename graph_traits< VertexListGraph >::vertex_iterator ui, ui_end;
    for (boost::tie(ui, ui_end) = vertices(g); ui != ui_end; ++ui)
    {
        put(distance, *ui, inf);
        put(pred, *ui, *ui);
    }

    put(distance, s, zero);
    vis.discover_vertex(s, g);
    typename std::vector< Vertex >::reverse_iterator i;
    for (i = rev_topo_order.rbegin(); i != rev_topo_order.rend(); ++i)
    {
        Vertex u = *i;
        vis.examine_vertex(u, g);
        typename graph_traits< VertexListGraph >::out_edge_iterator e, e_end;
        for (boost::tie(e, e_end) = out_edges(u, g); e != e_end; ++e)
        {
            vis.discover_vertex(target(*e, g), g);
            bool decreased
                = relax(*e, g, weight, pred, distance, combine, compare);
            if (decreased)
                vis.edge_relaxed(*e, g);
            else
                vis.edge_not_relaxed(*e, g);
        }
        vis.finish_vertex(u, g);
    }
}

namespace detail
{

    // Defaults are the same as Dijkstra's algorithm

    // Handle Distance Compare, Combine, Inf and Zero defaults
    template < class VertexListGraph, class DijkstraVisitor, class DistanceMap,
        class WeightMap, class ColorMap, class IndexMap, class Params >
    inline void dag_sp_dispatch2(const VertexListGraph& g,
        typename graph_traits< VertexListGraph >::vertex_descriptor s,
        DistanceMap distance, WeightMap weight, ColorMap color, IndexMap /*id*/,
        DijkstraVisitor vis, const Params& params)
    {
        typedef typename property_traits< DistanceMap >::value_type D;
        dummy_property_map p_map;
        D inf = choose_param(get_param(params, distance_inf_t()),
            (std::numeric_limits< D >::max)());
        dag_shortest_paths(g, s, distance, weight, color,
            choose_param(get_param(params, vertex_predecessor), p_map), vis,
            choose_param(
                get_param(params, distance_compare_t()), std::less< D >()),
            choose_param(
                get_param(params, distance_combine_t()), closed_plus< D >(inf)),
            inf, choose_param(get_param(params, distance_zero_t()), D()));
    }

    // Handle DistanceMap and ColorMap defaults
    template < class VertexListGraph, class DijkstraVisitor, class DistanceMap,
        class WeightMap, class ColorMap, class IndexMap, class Params >
    inline void dag_sp_dispatch1(const VertexListGraph& g,
        typename graph_traits< VertexListGraph >::vertex_descriptor s,
        DistanceMap distance, WeightMap weight, ColorMap color, IndexMap id,
        DijkstraVisitor vis, const Params& params)
    {
        typedef typename property_traits< WeightMap >::value_type T;
        typename std::vector< T >::size_type n;
        n = is_default_param(distance) ? num_vertices(g) : 1;
        std::vector< T > distance_map(n);
        n = is_default_param(color) ? num_vertices(g) : 1;
        std::vector< default_color_type > color_map(n);

        dag_sp_dispatch2(g, s,
            choose_param(distance,
                make_iterator_property_map(
                    distance_map.begin(), id, distance_map[0])),
            weight,
            choose_param(color,
                make_iterator_property_map(
                    color_map.begin(), id, color_map[0])),
            id, vis, params);
    }

} // namespace detail

template < class VertexListGraph, class Param, class Tag, class Rest >
inline void dag_shortest_paths(const VertexListGraph& g,
    typename graph_traits< VertexListGraph >::vertex_descriptor s,
    const bgl_named_params< Param, Tag, Rest >& params)
{
    // assert that the graph is directed...
    null_visitor null_vis;
    detail::dag_sp_dispatch1(g, s, get_param(params, vertex_distance),
        choose_const_pmap(get_param(params, edge_weight), g, edge_weight),
        get_param(params, vertex_color),
        choose_const_pmap(get_param(params, vertex_index), g, vertex_index),
        choose_param(
            get_param(params, graph_visitor), make_dijkstra_visitor(null_vis)),
        params);
}

} // namespace boost

#endif // BOOST_GRAPH_DAG_SHORTEST_PATHS_HPP