1 //

     2 //=======================================================================

     3 // Copyright 1997-2001 University of Notre Dame.

     4 // Authors: Andrew Lumsdaine, Lie-Quan Lee, Jeremy G. Siek

     5 //

     6 // Distributed under the Boost Software License, Version 1.0. (See

     7 // accompanying file LICENSE_1_0.txt or copy at

     8 // http://www.boost.org/LICENSE_1_0.txt)

     9 //=======================================================================

    10 //

    11 #ifndef BOOST_GRAPH_CONNECTED_COMPONENTS_HPP

    12 #define BOOST_GRAPH_CONNECTED_COMPONENTS_HPP

    13 

    14 #include <boost/config.hpp>

    15 #include <boost/graph/depth_first_search.hpp>

    16 #include <boost/graph/properties.hpp>

    17 #include <boost/graph/graph_concepts.hpp>

    18 

    19 #include <boost/static_assert.hpp>

    20 

    21 namespace boost {

    22 

    23   namespace detail {

    24 

    25     // This visitor is used both in the connected_components algorithm

    26     // and in the kosaraju strong components algorithm during the

    27     // second DFS traversal.

    28     template <class ComponentsMap>

    29     class components_recorder : public dfs_visitor<>

    30     {

    31       typedef typename property_traits<ComponentsMap>::value_type comp_type;

    32     public:

    33       components_recorder(ComponentsMap c, 

    34                           comp_type& c_count)

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

    36 

    37       template <class Vertex, class Graph>

    38       void start_vertex(Vertex, Graph&) {

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

    40           m_count = 0; // start counting components at zero

    41         else

    42           ++m_count;

    43       }

    44       template <class Vertex, class Graph>

    45       void discover_vertex(Vertex u, Graph&) {

    46         put(m_component, u, m_count);

    47       }

    48     protected:

    49       ComponentsMap m_component;

    50       comp_type& m_count;

    51     };

    52 

    53   } // namespace detail

    54 

    55   // This function computes the connected components of an undirected

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

    57 

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

    59   inline typename property_traits<ComponentMap>::value_type

    60   connected_components(const Graph& g, ComponentMap c, 

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

    62   {

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

    64 

    65     typedef typename graph_traits<Graph>::vertex_descriptor Vertex;

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

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

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

    69 

    70     typedef typename property_traits<ComponentMap>::value_type comp_type;

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

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

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

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

    75     return c_count + 1;

    76   }

    77 

    78   template <class Graph, class ComponentMap>

    79   inline typename property_traits<ComponentMap>::value_type

    80   connected_components(const Graph& g, ComponentMap c)

    81   {

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

    83 

    84     typedef typename graph_traits<Graph>::vertex_descriptor Vertex;

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

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

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

    88 

    89     typedef typename property_traits<ComponentMap>::value_type comp_type;

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

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

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

    93     depth_first_search(g, visitor(vis));

    94     return c_count + 1;

    95   }

    96 

    97   

    98 } // namespace boost

    99 

   100 

   101 #endif // BOOST_GRAPH_CONNECTED_COMPONENTS_HPP