//

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

 // Copyright 1997-2001 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_CONNECTED_COMPONENTS_HPP

 #define BOOST_GRAPH_CONNECTED_COMPONENTS_HPP

 #include <boost/config.hpp>

 #include <boost/graph/depth_first_search.hpp>

 #include <boost/graph/properties.hpp>

 #include <boost/graph/graph_concepts.hpp>

 #include <boost/static_assert.hpp>

 namespace boost {

   namespace detail {

     // This visitor is used both in the connected_components algorithm

     // and in the kosaraju strong components algorithm during the

     // second DFS traversal.

     template <class ComponentsMap>

     class components_recorder : public dfs_visitor<>

     {

       typedef typename property_traits<ComponentsMap>::value_type comp_type;

     public:

       components_recorder(ComponentsMap c, 

                           comp_type& c_count)

         : m_component(c), m_count(c_count) {}

       template <class Vertex, class Graph>

       void start_vertex(Vertex, Graph&) {

         if (m_count == (std::numeric_limits<comp_type>::max)())

           m_count = 0; // start counting components at zero

         else

           ++m_count;

       }

       template <class Vertex, class Graph>

       void discover_vertex(Vertex u, Graph&) {

         put(m_component, u, m_count);

       }

     protected:

       ComponentsMap m_component;

       comp_type& m_count;

     };

   } // namespace detail

   // This function computes the connected components of an undirected

   // graph using a single application of depth first search.

   template <class Graph, class ComponentMap, class P, class T, class R>

   inline typename property_traits<ComponentMap>::value_type

   connected_components(const Graph& g, ComponentMap c, 

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

   {

     if (num_vertices(g) == 0) return 0;

     typedef typename graph_traits<Graph>::vertex_descriptor Vertex;

     function_requires< WritablePropertyMapConcept<ComponentMap, Vertex> >();

     typedef typename boost::graph_traits<Graph>::directed_category directed;

     BOOST_STATIC_ASSERT((boost::is_same<directed, undirected_tag>::value));

     typedef typename property_traits<ComponentMap>::value_type comp_type;

     // c_count initialized to "nil" (with nil represented by (max)())

     comp_type c_count((std::numeric_limits<comp_type>::max)());

     detail::components_recorder<ComponentMap> vis(c, c_count);

     depth_first_search(g, params.visitor(vis));

     return c_count + 1;

   }

   template <class Graph, class ComponentMap>

   inline typename property_traits<ComponentMap>::value_type

   connected_components(const Graph& g, ComponentMap c)

   {

     if (num_vertices(g) == 0) return 0;

     typedef typename graph_traits<Graph>::vertex_descriptor Vertex;

     function_requires< WritablePropertyMapConcept<ComponentMap, Vertex> >();

     typedef typename boost::graph_traits<Graph>::directed_category directed;

     BOOST_STATIC_ASSERT((boost::is_same<directed, undirected_tag>::value));

     typedef typename property_traits<ComponentMap>::value_type comp_type;

     // c_count initialized to "nil" (with nil represented by (max)())

     comp_type c_count((std::numeric_limits<comp_type>::max)());

     detail::components_recorder<ComponentMap> vis(c, c_count);

     depth_first_search(g, visitor(vis));

     return c_count + 1;

   }

 } // namespace boost

 #endif // BOOST_GRAPH_CONNECTED_COMPONENTS_HPP