boost/graph/incremental_components.hpp
// //======================================================================= // Copyright 1997-2001 University of Notre Dame. // Copyright 2009 Trustees of Indiana University. // Authors: Andrew Lumsdaine, Lie-Quan Lee, Jeremy G. Siek, Michael Hansen // // 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_INCREMENTAL_COMPONENTS_HPP #define BOOST_INCREMENTAL_COMPONENTS_HPP #include <boost/detail/iterator.hpp> #include <boost/graph/detail/incremental_components.hpp> #include <boost/iterator/counting_iterator.hpp> #include <boost/make_shared.hpp> #include <boost/pending/disjoint_sets.hpp> #include <iterator> namespace boost { // A connected component algorithm for the case when dynamically // adding (but not removing) edges is common. The // incremental_components() function is a preparing operation. Call // same_component to check whether two vertices are in the same // component, or use disjoint_set::find_set to determine the // representative for a vertex. // This version of connected components does not require a full // Graph. Instead, it just needs an edge list, where the vertices of // each edge need to be of integer type. The edges are assumed to // be undirected. The other difference is that the result is stored in // a container, instead of just a decorator. The container should be // empty before the algorithm is called. It will grow during the // course of the algorithm. The container must be a model of // BackInsertionSequence and RandomAccessContainer // (std::vector is a good choice). After running the algorithm the // index container will map each vertex to the representative // vertex of the component to which it belongs. // // Adapted from an implementation by Alex Stepanov. The disjoint // sets data structure is from Tarjan's "Data Structures and Network // Algorithms", and the application to connected components is // similar to the algorithm described in Ch. 22 of "Intro to // Algorithms" by Cormen, et. all. // // An implementation of disjoint sets can be found in // boost/pending/disjoint_sets.hpp template <class EdgeListGraph, class DisjointSets> void incremental_components(EdgeListGraph& g, DisjointSets& ds) { typename graph_traits<EdgeListGraph>::edge_iterator e, end; for (boost::tie(e,end) = edges(g); e != end; ++e) ds.union_set(source(*e,g),target(*e,g)); } template <class ParentIterator> void compress_components(ParentIterator first, ParentIterator last) { for (ParentIterator current = first; current != last; ++current) detail::find_representative_with_full_compression(first, current-first); } template <class ParentIterator> typename boost::detail::iterator_traits<ParentIterator>::difference_type component_count(ParentIterator first, ParentIterator last) { std::ptrdiff_t count = 0; for (ParentIterator current = first; current != last; ++current) if (*current == current - first) ++count; return count; } // This algorithm can be applied to the result container of the // connected_components algorithm to normalize // the components. template <class ParentIterator> void normalize_components(ParentIterator first, ParentIterator last) { for (ParentIterator current = first; current != last; ++current) detail::normalize_node(first, current - first); } template <class VertexListGraph, class DisjointSets> void initialize_incremental_components(VertexListGraph& G, DisjointSets& ds) { typename graph_traits<VertexListGraph> ::vertex_iterator v, vend; for (boost::tie(v, vend) = vertices(G); v != vend; ++v) ds.make_set(*v); } template <class Vertex, class DisjointSet> inline bool same_component(Vertex u, Vertex v, DisjointSet& ds) { return ds.find_set(u) == ds.find_set(v); } // Class that builds a quick-access indexed linked list that allows // for fast iterating through a parent component's children. template <typename IndexType> class component_index { private: typedef std::vector<IndexType> IndexContainer; public: typedef counting_iterator<IndexType> iterator; typedef iterator const_iterator; typedef IndexType value_type; typedef IndexType size_type; typedef detail::component_index_iterator<typename IndexContainer::iterator> component_iterator; public: template <typename ParentIterator, typename ElementIndexMap> component_index(ParentIterator parent_start, ParentIterator parent_end, const ElementIndexMap& index_map) : m_num_elements(std::distance(parent_start, parent_end)), m_components(make_shared<IndexContainer>()), m_index_list(make_shared<IndexContainer>(m_num_elements)) { build_index_lists(parent_start, index_map); } // component_index template <typename ParentIterator> component_index(ParentIterator parent_start, ParentIterator parent_end) : m_num_elements(std::distance(parent_start, parent_end)), m_components(make_shared<IndexContainer>()), m_index_list(make_shared<IndexContainer>(m_num_elements)) { build_index_lists(parent_start, boost::identity_property_map()); } // component_index // Returns the number of components inline std::size_t size() const { return (m_components->size()); } // Beginning iterator for component indices iterator begin() const { return (iterator(0)); } // End iterator for component indices iterator end() const { return (iterator(this->size())); } // Returns a pair of begin and end iterators for the child // elements of component [component_index]. std::pair<component_iterator, component_iterator> operator[](IndexType component_index) const { IndexType first_index = (*m_components)[component_index]; return (std::make_pair (component_iterator(m_index_list->begin(), first_index), component_iterator(m_num_elements))); } private: template <typename ParentIterator, typename ElementIndexMap> void build_index_lists(ParentIterator parent_start, const ElementIndexMap& index_map) { typedef typename std::iterator_traits<ParentIterator>::value_type Element; typename IndexContainer::iterator index_list = m_index_list->begin(); // First pass - find root elements, construct index list for (IndexType element_index = 0; element_index < m_num_elements; ++element_index) { Element parent_element = parent_start[element_index]; IndexType parent_index = get(index_map, parent_element); if (element_index != parent_index) { index_list[element_index] = parent_index; } else { m_components->push_back(element_index); // m_num_elements is the linked list terminator index_list[element_index] = m_num_elements; } } // Second pass - build linked list for (IndexType element_index = 0; element_index < m_num_elements; ++element_index) { Element parent_element = parent_start[element_index]; IndexType parent_index = get(index_map, parent_element); if (element_index != parent_index) { // Follow list until a component parent is found while (index_list[parent_index] != m_num_elements) { parent_index = index_list[parent_index]; } // Push element to the front of the linked list index_list[element_index] = index_list[parent_index]; index_list[parent_index] = element_index; } } } // build_index_lists protected: IndexType m_num_elements; shared_ptr<IndexContainer> m_components, m_index_list; }; // class component_index } // namespace boost #endif // BOOST_INCREMENTAL_COMPONENTS_HPP