boost/graph/connected_components.hpp

   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 #include <boost/graph/overloading.hpp>
  19 #include <boost/static_assert.hpp>
  20 #include <boost/concept/assert.hpp>
  21
  22 namespace boost {
  23
  24   namespace detail {
  25
  26     // This visitor is used both in the connected_components algorithm
  27     // and in the kosaraju strong components algorithm during the
  28     // second DFS traversal.
  29     template <class ComponentsMap>
  30     class components_recorder : public dfs_visitor<>
  31     {
  32       typedef typename property_traits<ComponentsMap>::value_type comp_type;
  33     public:
  34       components_recorder(ComponentsMap c,
  35                           comp_type& c_count)
  36         : m_component(c), m_count(c_count) {}
  37
  38       template <class Vertex, class Graph>
  39       void start_vertex(Vertex, Graph&) {
  40         if (m_count == (std::numeric_limits<comp_type>::max)())
  41           m_count = 0; // start counting components at zero
  42         else
  43           ++m_count;
  44       }
  45       template <class Vertex, class Graph>
  46       void discover_vertex(Vertex u, Graph&) {
  47         put(m_component, u, m_count);
  48       }
  49     protected:
  50       ComponentsMap m_component;
  51       comp_type& m_count;
  52     };
  53
  54   } // namespace detail
  55
  56   // This function computes the connected components of an undirected
  57   // graph using a single application of depth first search.
  58
  59   template <class Graph, class ComponentMap, class P, class T, class R>
  60   inline typename property_traits<ComponentMap>::value_type
  61   connected_components(const Graph& g, ComponentMap c,
  62                        const bgl_named_params<P, T, R>& params
  63                        BOOST_GRAPH_ENABLE_IF_MODELS_PARM(Graph, vertex_list_graph_tag))
  64   {
  65     if (num_vertices(g) == 0) return 0;
  66
  67     typedef typename graph_traits<Graph>::vertex_descriptor Vertex;
  68     BOOST_CONCEPT_ASSERT(( WritablePropertyMapConcept<ComponentMap, Vertex> ));
  69     typedef typename boost::graph_traits<Graph>::directed_category directed;
  70     BOOST_STATIC_ASSERT((boost::is_same<directed, undirected_tag>::value));
  71
  72     typedef typename property_traits<ComponentMap>::value_type comp_type;
  73     // c_count initialized to "nil" (with nil represented by (max)())
  74     comp_type c_count((std::numeric_limits<comp_type>::max)());
  75     detail::components_recorder<ComponentMap> vis(c, c_count);
  76     depth_first_search(g, params.visitor(vis));
  77     return c_count + 1;
  78   }
  79
  80   template <class Graph, class ComponentMap>
  81   inline typename property_traits<ComponentMap>::value_type
  82   connected_components(const Graph& g, ComponentMap c
  83                        BOOST_GRAPH_ENABLE_IF_MODELS_PARM(Graph, vertex_list_graph_tag))
  84   {
  85     if (num_vertices(g) == 0) return 0;
  86
  87     typedef typename graph_traits<Graph>::vertex_descriptor Vertex;
  88     BOOST_CONCEPT_ASSERT(( WritablePropertyMapConcept<ComponentMap, Vertex> ));
  89     typedef typename boost::graph_traits<Graph>::directed_category directed;
  90     // BOOST_STATIC_ASSERT((boost::is_same<directed, undirected_tag>::value));
  91
  92     typedef typename property_traits<ComponentMap>::value_type comp_type;
  93     // c_count initialized to "nil" (with nil represented by (max)())
  94     comp_type c_count((std::numeric_limits<comp_type>::max)());
  95     detail::components_recorder<ComponentMap> vis(c, c_count);
  96     depth_first_search(g, visitor(vis));
  97     return c_count + 1;
  98   }
  99
 100
 101 } // namespace boost
 102
 103 #ifdef BOOST_GRAPH_USE_MPI
 104 #  include <boost/graph/distributed/connected_components.hpp>
 105 #endif
 106
 107 #endif // BOOST_GRAPH_CONNECTED_COMPONENTS_HPP