//

 //=======================================================================

 // Copyright 1997, 1998, 1999, 2000 University of Notre Dame.

 // 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_TOPOLOGICAL_SORT_HPP

 #define BOOST_GRAPH_TOPOLOGICAL_SORT_HPP

 #include <boost/config.hpp>

 #include <boost/property_map.hpp>

 #include <boost/graph/depth_first_search.hpp>

 #include <boost/graph/visitors.hpp>

 #include <boost/graph/exception.hpp>

 namespace boost { 

   // Topological sort visitor

   //

   // This visitor merely writes the linear ordering into an

   // OutputIterator. The OutputIterator could be something like an

   // ostream_iterator, or it could be a back/front_insert_iterator.

   // Note that if it is a back_insert_iterator, the recorded order is

   // the reverse topological order. On the other hand, if it is a

   // front_insert_iterator, the recorded order is the topological

   // order.

   //

   template <typename OutputIterator>

   struct topo_sort_visitor : public dfs_visitor<>

   {

     topo_sort_visitor(OutputIterator _iter)

       : m_iter(_iter) { }

     template <typename Edge, typename Graph>

     void back_edge(const Edge& u, Graph&) { throw not_a_dag(); }

     template <typename Vertex, typename Graph> 

     void finish_vertex(const Vertex& u, Graph&) { *m_iter++ = u; }

     OutputIterator m_iter;

   };

   // Topological Sort

   //

   // The topological sort algorithm creates a linear ordering

   // of the vertices such that if edge (u,v) appears in the graph,

   // then u comes before v in the ordering. The graph must

   // be a directed acyclic graph (DAG). The implementation

   // consists mainly of a call to depth-first search.

   //

   template <typename VertexListGraph, typename OutputIterator,

     typename P, typename T, typename R>

   void topological_sort(VertexListGraph& g, OutputIterator result,

                         const bgl_named_params<P, T, R>& params)

   {

     typedef topo_sort_visitor<OutputIterator> TopoVisitor;

     depth_first_search(g, params.visitor(TopoVisitor(result)));

   }

   template <typename VertexListGraph, typename OutputIterator>

   void topological_sort(VertexListGraph& g, OutputIterator result)

   {

     topological_sort(g, result, 

                      bgl_named_params<int, buffer_param_t>(0)); // bogus

   }

 } // namespace boost

 #endif /*BOOST_GRAPH_TOPOLOGICAL_SORT_H*/