Boost C++ Libraries

libs/graph/example/roget_components.cpp

//=======================================================================
// Copyright 2001 University of Notre Dame.
// Authors: Jeremy G. Siek, Andrew Lumsdaine, Lie-Quan Lee
//
// 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 <cstdio>
#include <cstring>
#include <iostream>
#include <boost/graph/stanford_graph.hpp>
#include <boost/graph/strong_components.hpp>

#define specs(v) (filename ? index_map[v] : v->cat_no) << " " << v->name

int main(int argc, char* argv[])
{
    using namespace boost;
    Graph* g;
    typedef graph_traits< Graph* >::vertex_descriptor vertex_t;
    unsigned long n = 0;
    unsigned long d = 0;
    unsigned long p = 0;
    long s = 0;
    char* filename = NULL;
    int c, i;

    while (--argc)
    {
        if (sscanf(argv[argc], "-n%lu", &n) == 1)
            ;
        else if (sscanf(argv[argc], "-d%lu", &d) == 1)
            ;
        else if (sscanf(argv[argc], "-p%lu", &p) == 1)
            ;
        else if (sscanf(argv[argc], "-s%ld", &s) == 1)
            ;
        else if (strncmp(argv[argc], "-g", 2) == 0)
            filename = argv[argc] + 2;
        else
        {
            fprintf(stderr, "Usage: %s [-nN][-dN][-pN][-sN][-gfoo]\n", argv[0]);
            return -2;
        }
    }

    g = (filename ? restore_graph(filename) : roget(n, d, p, s));
    if (g == NULL)
    {
        fprintf(stderr, "Sorry, can't create the graph! (error code %ld)\n",
            panic_code);
        return -1;
    }
    printf("Reachability analysis of %s\n\n", g->id);

    // - The root map corresponds to what Knuth calls the "min" field.
    // - The discover time map is the "rank" field
    // - Knuth uses the rank field for double duty, to record the
    //   discover time, and to keep track of which vertices have
    //   been visited. The BGL strong_components() function needs
    //   a separate field for marking colors, so we use the w field.

    std::vector< int > comp(num_vertices(g));
    property_map< Graph*, vertex_index_t >::type index_map
        = get(vertex_index, g);

    property_map< Graph*, v_property< vertex_t > >::type root
        = get(v_property< vertex_t >(), g);

    int num_comp = strong_components(g,
        make_iterator_property_map(comp.begin(), index_map),
        root_map(root)
            .discover_time_map(get(z_property< long >(), g))
            .color_map(get(w_property< long >(), g)));

    std::vector< std::vector< vertex_t > > strong_comp(num_comp);

    // First add representative vertices to each component's list
    graph_traits< Graph* >::vertex_iterator vi, vi_end;
    for (boost::tie(vi, vi_end) = vertices(g); vi != vi_end; ++vi)
        if (root[*vi] == *vi)
            strong_comp[comp[index_map[*vi]]].push_back(*vi);

    // Then add the other vertices of the component
    for (boost::tie(vi, vi_end) = vertices(g); vi != vi_end; ++vi)
        if (root[*vi] != *vi)
            strong_comp[comp[index_map[*vi]]].push_back(*vi);

    // We do not print out the "from" and "to" information as Knuth
    // does because we no longer have easy access to that information
    // from outside the algorithm.

    for (c = 0; c < num_comp; ++c)
    {
        vertex_t v = strong_comp[c].front();
        std::cout << "Strong component `" << specs(v) << "'";
        if (strong_comp[c].size() > 1)
        {
            std::cout << " also includes:\n";
            for (i = 1; i < strong_comp[c].size(); ++i)
                std::cout << " " << specs(strong_comp[c][i]) << std::endl;
        }
        else
            std::cout << std::endl;
    }

    // Next we print out the "component graph" or "condensation", that
    // is, we consider each component to be a vertex in a new graph
    // where there is an edge connecting one component to another if there
    // is one or more edges connecting any of the vertices from the
    // first component to any of the vertices in the second. We use the
    // name of the representative vertex as the name of the component.

    printf("\nLinks between components:\n");

    // This array provides an efficient way to check if we've already
    // created a link from the current component to the component
    // of the target vertex.
    std::vector< int > mark(num_comp, (std::numeric_limits< int >::max)());

    // We go in reverse order just to mimic the output ordering in
    // Knuth's version.
    for (c = num_comp - 1; c >= 0; --c)
    {
        vertex_t u = strong_comp[c][0];
        for (i = 0; i < strong_comp[c].size(); ++i)
        {
            vertex_t v = strong_comp[c][i];
            graph_traits< Graph* >::out_edge_iterator ei, ei_end;
            for (boost::tie(ei, ei_end) = out_edges(v, g); ei != ei_end; ++ei)
            {
                vertex_t x = target(*ei, g);
                int comp_x = comp[index_map[x]];
                if (comp_x != c && mark[comp_x] != c)
                {
                    mark[comp_x] = c;
                    vertex_t w = strong_comp[comp_x][0];
                    std::cout << specs(u) << " -> " << specs(w) << " (e.g., "
                              << specs(v) << " -> " << specs(x) << ")\n";
                } // if
            } // for
        } // for
    } // for
}