1 | //=======================================================================
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2 | // Copyright 2015 by Ireneusz Szcześniak
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3 | // Authors: Ireneusz Szcześniak
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4 | //
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5 | // Distributed under the Boost Software License, Version 1.0. (See
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6 | // accompanying file LICENSE_1_0.txt or copy at
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7 | // http://www.boost.org/LICENSE_1_0.txt)
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8 | //=======================================================================
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9 |
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10 | //=======================================================================
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11 | // Function edge_disjoint_ksp finds the k-shortest paths which are
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12 | // edge-disjoint, i.e. the paths do not have common edges. The graph
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13 | // can have parallel edges. The algorithm employs the Dijkstra
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14 | // algorithm to find the shortest path. Next the edges of the found
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15 | // path are disabled, and Dijkstra finds the second shortest path.
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16 | // This process is repeated until k paths are found or there are no
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17 | // more paths to be found.
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18 | // =======================================================================
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19 |
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20 | #ifndef BOOST_GRAPH_EDGE_DISJOINT_KSP
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21 | #define BOOST_GRAPH_EDGE_DISJOINT_KSP
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22 |
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23 | #include <list>
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24 | #include <set>
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25 |
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26 | #include <boost/graph/filtered_graph.hpp>
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27 | #include <boost/optional.hpp>
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28 |
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29 | #include "custom_dijkstra_call.hpp"
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30 |
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31 | namespace boost {
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32 |
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33 | //========================================================================
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34 | // The implementation of the k-shortest paths algorithm.
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35 | //========================================================================
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36 |
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37 | template <typename Graph, typename WeightMap, typename IndexMap>
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38 | std::list<std::pair<typename WeightMap::value_type,
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39 | std::list<typename Graph::edge_descriptor>>>
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40 | edge_disjoint_ksp(const Graph& g,
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41 | typename Graph::vertex_descriptor s,
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42 | typename Graph::vertex_descriptor t,
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43 | WeightMap wm, IndexMap im,
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44 | optional<unsigned> K)
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45 | {
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46 | typedef typename Graph::vertex_descriptor vertex_descriptor;
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47 | typedef typename Graph::edge_descriptor edge_descriptor;
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48 | typedef typename WeightMap::value_type weight_type;
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49 | typedef std::set<edge_descriptor> es_type;
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50 | typedef std::list<edge_descriptor> path_type;
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51 | typedef std::pair<weight_type, path_type> kr_type;
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52 | typedef filtered_graph<Graph, is_not_in_subset<es_type>> fg_type;
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53 |
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54 | // The result.
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55 | std::list<std::pair<weight_type, path_type>> result;
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56 |
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57 | // The set of excluded edges.
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58 | es_type excluded;
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59 | // The edge predicate.
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60 | is_not_in_subset<es_type> ep(excluded);
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61 | // The filtered graph.
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62 | fg_type fg(g, ep);
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63 |
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64 | // In each iteration, we try to find a shortest path.
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65 | do
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66 | {
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67 | // If required, stop at the K-th shortest path.
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68 | if (K && result.size() == K.get())
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69 | break;
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70 |
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71 | // This is the optional k-th result.
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72 | optional<kr_type> okr = custom_dijkstra_call(fg, s, t, wm, im);
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73 |
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74 | if (!okr)
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75 | break;
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76 |
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77 | // This is the k-th result.
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78 | const kr_type &kr = okr.get();
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79 |
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80 | // Exclude the edges from the k-th result found.
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81 | for(auto const &e: kr.second)
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82 | excluded.insert(e);
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83 |
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84 | result.push_back(kr);
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85 |
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86 | } while(true);
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87 |
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88 | return result;
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89 | }
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90 |
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91 | //========================================================================
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92 | // A helper function to figure out the default weight map of the graph.
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93 | //========================================================================
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94 |
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95 | template <typename Graph>
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96 | std::list<std::pair<typename property_map<Graph, edge_weight_t>::value_type,
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97 | std::list<typename Graph::edge_descriptor>>>
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98 | edge_disjoint_ksp(const Graph& g,
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99 | typename Graph::vertex_descriptor s,
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100 | typename Graph::vertex_descriptor t,
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101 | optional<unsigned> K = optional<unsigned>())
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102 | {
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103 | return edge_disjoint_ksp(g, s, t, get(edge_weight_t(), g),
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104 | get(vertex_index_t(), g), K);
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105 | }
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106 |
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107 | } // boost
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108 |
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109 | #endif /* BOOST_GRAPH_EDGE_DISJOINT_KSP */
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