Boost C++ Libraries

libs/graph/example/incremental_components.cpp

//=======================================================================
// Copyright 1997, 1998, 1999, 2000 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)
//=======================================================================
#include <iostream>
#include <vector>

#include <boost/foreach.hpp>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graph_utility.hpp>
#include <boost/graph/incremental_components.hpp>
#include <boost/pending/disjoint_sets.hpp>

/*

  This example shows how to use the disjoint set data structure
  to compute the connected components of an undirected, changing
  graph.

  Sample output:

  An undirected graph:
  0 <--> 1 4
  1 <--> 0 4
  2 <--> 5
  3 <-->
  4 <--> 1 0
  5 <--> 2

  representative[0] = 1
  representative[1] = 1
  representative[2] = 5
  representative[3] = 3
  representative[4] = 1
  representative[5] = 5

  component 0 contains: 4 1 0
  component 1 contains: 3
  component 2 contains: 5 2

 */

using namespace boost;

int main(int argc, char* argv[])
{
    typedef adjacency_list< vecS, vecS, undirectedS > Graph;
    typedef graph_traits< Graph >::vertex_descriptor Vertex;
    typedef graph_traits< Graph >::vertices_size_type VertexIndex;

    const int VERTEX_COUNT = 6;
    Graph graph(VERTEX_COUNT);

    std::vector< VertexIndex > rank(num_vertices(graph));
    std::vector< Vertex > parent(num_vertices(graph));

    typedef VertexIndex* Rank;
    typedef Vertex* Parent;

    disjoint_sets< Rank, Parent > ds(&rank[0], &parent[0]);

    initialize_incremental_components(graph, ds);
    incremental_components(graph, ds);

    graph_traits< Graph >::edge_descriptor edge;
    bool flag;

    boost::tie(edge, flag) = add_edge(0, 1, graph);
    ds.union_set(0, 1);

    boost::tie(edge, flag) = add_edge(1, 4, graph);
    ds.union_set(1, 4);

    boost::tie(edge, flag) = add_edge(4, 0, graph);
    ds.union_set(4, 0);

    boost::tie(edge, flag) = add_edge(2, 5, graph);
    ds.union_set(2, 5);

    std::cout << "An undirected graph:" << std::endl;
    print_graph(graph, get(boost::vertex_index, graph));
    std::cout << std::endl;

    BOOST_FOREACH (Vertex current_vertex, vertices(graph))
    {
        std::cout << "representative[" << current_vertex
                  << "] = " << ds.find_set(current_vertex) << std::endl;
    }

    std::cout << std::endl;

    typedef component_index< VertexIndex > Components;

    // NOTE: Because we're using vecS for the graph type, we're
    // effectively using identity_property_map for a vertex index map.
    // If we were to use listS instead, the index map would need to be
    // explicitly passed to the component_index constructor.
    Components components(parent.begin(), parent.end());

    // Iterate through the component indices
    BOOST_FOREACH (VertexIndex current_index, components)
    {
        std::cout << "component " << current_index << " contains: ";

        // Iterate through the child vertex indices for [current_index]
        BOOST_FOREACH (VertexIndex child_index, components[current_index])
        {
            std::cout << child_index << " ";
        }

        std::cout << std::endl;
    }

    return (0);
}