1 | /* -*- C++ -*- |
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2 | * |
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3 | * This file is a part of LEMON, a generic C++ optimization library |
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4 | * |
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5 | * Copyright (C) 2003-2008 |
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6 | * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport |
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7 | * (Egervary Research Group on Combinatorial Optimization, EGRES). |
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8 | * |
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9 | * Permission to use, modify and distribute this software is granted |
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10 | * provided that this copyright notice appears in all copies. For |
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11 | * precise terms see the accompanying LICENSE file. |
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12 | * |
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13 | * This software is provided "AS IS" with no warranty of any kind, |
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14 | * express or implied, and with no claim as to its suitability for any |
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15 | * purpose. |
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16 | * |
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17 | */ |
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18 | |
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19 | #ifndef LEMON_SUURBALLE_H |
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20 | #define LEMON_SUURBALLE_H |
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21 | |
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22 | ///\ingroup shortest_path |
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23 | ///\file |
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24 | ///\brief An algorithm for finding arc-disjoint paths between two |
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25 | /// nodes having minimum total length. |
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26 | |
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27 | #include <vector> |
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28 | #include <lemon/bin_heap.h> |
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29 | #include <lemon/path.h> |
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30 | |
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31 | namespace lemon { |
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32 | |
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33 | /// \addtogroup shortest_path |
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34 | /// @{ |
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35 | |
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36 | /// \brief Algorithm for finding arc-disjoint paths between two nodes |
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37 | /// having minimum total length. |
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38 | /// |
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39 | /// \ref lemon::Suurballe "Suurballe" implements an algorithm for |
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40 | /// finding arc-disjoint paths having minimum total length (cost) |
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41 | /// from a given source node to a given target node in a digraph. |
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42 | /// |
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43 | /// In fact, this implementation is the specialization of the |
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44 | /// \ref CapacityScaling "successive shortest path" algorithm. |
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45 | /// |
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46 | /// \tparam Digraph The digraph type the algorithm runs on. |
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47 | /// The default value is \c ListDigraph. |
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48 | /// \tparam LengthMap The type of the length (cost) map. |
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49 | /// The default value is <tt>Digraph::ArcMap<int></tt>. |
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50 | /// |
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51 | /// \warning Length values should be \e non-negative \e integers. |
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52 | /// |
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53 | /// \note For finding node-disjoint paths this algorithm can be used |
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54 | /// with \ref SplitNodes. |
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55 | #ifdef DOXYGEN |
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56 | template <typename Digraph, typename LengthMap> |
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57 | #else |
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58 | template < typename Digraph = ListDigraph, |
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59 | typename LengthMap = typename Digraph::template ArcMap<int> > |
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60 | #endif |
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61 | class Suurballe |
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62 | { |
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63 | TEMPLATE_DIGRAPH_TYPEDEFS(Digraph); |
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64 | |
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65 | typedef typename LengthMap::Value Length; |
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66 | typedef ConstMap<Arc, int> ConstArcMap; |
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67 | typedef typename Digraph::template NodeMap<Arc> PredMap; |
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68 | |
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69 | public: |
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70 | |
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71 | /// The type of the flow map. |
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72 | typedef typename Digraph::template ArcMap<int> FlowMap; |
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73 | /// The type of the potential map. |
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74 | typedef typename Digraph::template NodeMap<Length> PotentialMap; |
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75 | /// The type of the path structures. |
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76 | typedef SimplePath<Digraph> Path; |
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77 | |
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78 | private: |
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79 | |
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80 | /// \brief Special implementation of the Dijkstra algorithm |
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81 | /// for finding shortest paths in the residual network. |
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82 | /// |
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83 | /// \ref ResidualDijkstra is a special implementation of the |
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84 | /// \ref Dijkstra algorithm for finding shortest paths in the |
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85 | /// residual network of the digraph with respect to the reduced arc |
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86 | /// lengths and modifying the node potentials according to the |
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87 | /// distance of the nodes. |
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88 | class ResidualDijkstra |
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89 | { |
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90 | typedef typename Digraph::template NodeMap<int> HeapCrossRef; |
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91 | typedef BinHeap<Length, HeapCrossRef> Heap; |
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92 | |
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93 | private: |
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94 | |
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95 | // The digraph the algorithm runs on |
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96 | const Digraph &_graph; |
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97 | |
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98 | // The main maps |
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99 | const FlowMap &_flow; |
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100 | const LengthMap &_length; |
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101 | PotentialMap &_potential; |
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102 | |
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103 | // The distance map |
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104 | PotentialMap _dist; |
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105 | // The pred arc map |
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106 | PredMap &_pred; |
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107 | // The processed (i.e. permanently labeled) nodes |
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108 | std::vector<Node> _proc_nodes; |
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109 | |
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110 | Node _s; |
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111 | Node _t; |
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112 | |
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113 | public: |
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114 | |
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115 | /// Constructor. |
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116 | ResidualDijkstra( const Digraph &digraph, |
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117 | const FlowMap &flow, |
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118 | const LengthMap &length, |
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119 | PotentialMap &potential, |
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120 | PredMap &pred, |
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121 | Node s, Node t ) : |
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122 | _graph(digraph), _flow(flow), _length(length), _potential(potential), |
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123 | _dist(digraph), _pred(pred), _s(s), _t(t) {} |
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124 | |
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125 | /// \brief Run the algorithm. It returns \c true if a path is found |
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126 | /// from the source node to the target node. |
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127 | bool run() { |
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128 | HeapCrossRef heap_cross_ref(_graph, Heap::PRE_HEAP); |
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129 | Heap heap(heap_cross_ref); |
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130 | heap.push(_s, 0); |
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131 | _pred[_s] = INVALID; |
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132 | _proc_nodes.clear(); |
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133 | |
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134 | // Process nodes |
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135 | while (!heap.empty() && heap.top() != _t) { |
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136 | Node u = heap.top(), v; |
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137 | Length d = heap.prio() + _potential[u], nd; |
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138 | _dist[u] = heap.prio(); |
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139 | heap.pop(); |
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140 | _proc_nodes.push_back(u); |
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141 | |
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142 | // Traverse outgoing arcs |
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143 | for (OutArcIt e(_graph, u); e != INVALID; ++e) { |
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144 | if (_flow[e] == 0) { |
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145 | v = _graph.target(e); |
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146 | switch(heap.state(v)) { |
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147 | case Heap::PRE_HEAP: |
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148 | heap.push(v, d + _length[e] - _potential[v]); |
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149 | _pred[v] = e; |
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150 | break; |
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151 | case Heap::IN_HEAP: |
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152 | nd = d + _length[e] - _potential[v]; |
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153 | if (nd < heap[v]) { |
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154 | heap.decrease(v, nd); |
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155 | _pred[v] = e; |
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156 | } |
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157 | break; |
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158 | case Heap::POST_HEAP: |
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159 | break; |
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160 | } |
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161 | } |
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162 | } |
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163 | |
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164 | // Traverse incoming arcs |
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165 | for (InArcIt e(_graph, u); e != INVALID; ++e) { |
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166 | if (_flow[e] == 1) { |
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167 | v = _graph.source(e); |
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168 | switch(heap.state(v)) { |
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169 | case Heap::PRE_HEAP: |
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170 | heap.push(v, d - _length[e] - _potential[v]); |
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171 | _pred[v] = e; |
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172 | break; |
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173 | case Heap::IN_HEAP: |
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174 | nd = d - _length[e] - _potential[v]; |
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175 | if (nd < heap[v]) { |
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176 | heap.decrease(v, nd); |
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177 | _pred[v] = e; |
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178 | } |
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179 | break; |
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180 | case Heap::POST_HEAP: |
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181 | break; |
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182 | } |
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183 | } |
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184 | } |
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185 | } |
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186 | if (heap.empty()) return false; |
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187 | |
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188 | // Update potentials of processed nodes |
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189 | Length t_dist = heap.prio(); |
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190 | for (int i = 0; i < int(_proc_nodes.size()); ++i) |
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191 | _potential[_proc_nodes[i]] += _dist[_proc_nodes[i]] - t_dist; |
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192 | return true; |
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193 | } |
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194 | |
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195 | }; //class ResidualDijkstra |
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196 | |
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197 | private: |
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198 | |
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199 | // The digraph the algorithm runs on |
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200 | const Digraph &_graph; |
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201 | // The length map |
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202 | const LengthMap &_length; |
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203 | |
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204 | // Arc map of the current flow |
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205 | FlowMap *_flow; |
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206 | bool _local_flow; |
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207 | // Node map of the current potentials |
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208 | PotentialMap *_potential; |
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209 | bool _local_potential; |
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210 | |
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211 | // The source node |
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212 | Node _source; |
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213 | // The target node |
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214 | Node _target; |
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215 | |
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216 | // Container to store the found paths |
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217 | std::vector< SimplePath<Digraph> > paths; |
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218 | int _path_num; |
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219 | |
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220 | // The pred arc map |
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221 | PredMap _pred; |
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222 | // Implementation of the Dijkstra algorithm for finding augmenting |
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223 | // shortest paths in the residual network |
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224 | ResidualDijkstra *_dijkstra; |
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225 | |
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226 | public: |
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227 | |
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228 | /// \brief Constructor. |
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229 | /// |
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230 | /// Constructor. |
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231 | /// |
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232 | /// \param digraph The digraph the algorithm runs on. |
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233 | /// \param length The length (cost) values of the arcs. |
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234 | /// \param s The source node. |
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235 | /// \param t The target node. |
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236 | Suurballe( const Digraph &digraph, |
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237 | const LengthMap &length, |
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238 | Node s, Node t ) : |
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239 | _graph(digraph), _length(length), _flow(0), _local_flow(false), |
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240 | _potential(0), _local_potential(false), _source(s), _target(t), |
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241 | _pred(digraph) {} |
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242 | |
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243 | /// Destructor. |
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244 | ~Suurballe() { |
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245 | if (_local_flow) delete _flow; |
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246 | if (_local_potential) delete _potential; |
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247 | delete _dijkstra; |
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248 | } |
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249 | |
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250 | /// \brief Set the flow map. |
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251 | /// |
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252 | /// This function sets the flow map. |
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253 | /// |
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254 | /// The found flow contains only 0 and 1 values. It is the union of |
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255 | /// the found arc-disjoint paths. |
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256 | /// |
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257 | /// \return \c (*this) |
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258 | Suurballe& flowMap(FlowMap &map) { |
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259 | if (_local_flow) { |
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260 | delete _flow; |
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261 | _local_flow = false; |
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262 | } |
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263 | _flow = ↦ |
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264 | return *this; |
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265 | } |
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266 | |
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267 | /// \brief Set the potential map. |
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268 | /// |
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269 | /// This function sets the potential map. |
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270 | /// |
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271 | /// The potentials provide the dual solution of the underlying |
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272 | /// minimum cost flow problem. |
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273 | /// |
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274 | /// \return \c (*this) |
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275 | Suurballe& potentialMap(PotentialMap &map) { |
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276 | if (_local_potential) { |
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277 | delete _potential; |
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278 | _local_potential = false; |
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279 | } |
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280 | _potential = ↦ |
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281 | return *this; |
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282 | } |
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283 | |
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284 | /// \name Execution control |
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285 | /// The simplest way to execute the algorithm is to call the run() |
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286 | /// function. |
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287 | /// \n |
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288 | /// If you only need the flow that is the union of the found |
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289 | /// arc-disjoint paths, you may call init() and findFlow(). |
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290 | |
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291 | /// @{ |
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292 | |
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293 | /// \brief Run the algorithm. |
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294 | /// |
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295 | /// This function runs the algorithm. |
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296 | /// |
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297 | /// \param k The number of paths to be found. |
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298 | /// |
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299 | /// \return \c k if there are at least \c k arc-disjoint paths from |
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300 | /// \c s to \c t in the digraph. Otherwise it returns the number of |
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301 | /// arc-disjoint paths found. |
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302 | /// |
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303 | /// \note Apart from the return value, <tt>s.run(k)</tt> is just a |
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304 | /// shortcut of the following code. |
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305 | /// \code |
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306 | /// s.init(); |
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307 | /// s.findFlow(k); |
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308 | /// s.findPaths(); |
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309 | /// \endcode |
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310 | int run(int k = 2) { |
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311 | init(); |
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312 | findFlow(k); |
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313 | findPaths(); |
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314 | return _path_num; |
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315 | } |
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316 | |
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317 | /// \brief Initialize the algorithm. |
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318 | /// |
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319 | /// This function initializes the algorithm. |
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320 | void init() { |
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321 | // Initialize maps |
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322 | if (!_flow) { |
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323 | _flow = new FlowMap(_graph); |
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324 | _local_flow = true; |
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325 | } |
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326 | if (!_potential) { |
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327 | _potential = new PotentialMap(_graph); |
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328 | _local_potential = true; |
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329 | } |
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330 | for (ArcIt e(_graph); e != INVALID; ++e) (*_flow)[e] = 0; |
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331 | for (NodeIt n(_graph); n != INVALID; ++n) (*_potential)[n] = 0; |
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332 | |
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333 | _dijkstra = new ResidualDijkstra( _graph, *_flow, _length, |
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334 | *_potential, _pred, |
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335 | _source, _target ); |
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336 | } |
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337 | |
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338 | /// \brief Execute the successive shortest path algorithm to find |
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339 | /// an optimal flow. |
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340 | /// |
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341 | /// This function executes the successive shortest path algorithm to |
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342 | /// find a minimum cost flow, which is the union of \c k or less |
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343 | /// arc-disjoint paths. |
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344 | /// |
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345 | /// \return \c k if there are at least \c k arc-disjoint paths from |
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346 | /// \c s to \c t in the digraph. Otherwise it returns the number of |
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347 | /// arc-disjoint paths found. |
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348 | /// |
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349 | /// \pre \ref init() must be called before using this function. |
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350 | int findFlow(int k = 2) { |
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351 | // Find shortest paths |
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352 | _path_num = 0; |
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353 | while (_path_num < k) { |
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354 | // Run Dijkstra |
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355 | if (!_dijkstra->run()) break; |
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356 | ++_path_num; |
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357 | |
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358 | // Set the flow along the found shortest path |
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359 | Node u = _target; |
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360 | Arc e; |
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361 | while ((e = _pred[u]) != INVALID) { |
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362 | if (u == _graph.target(e)) { |
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363 | (*_flow)[e] = 1; |
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364 | u = _graph.source(e); |
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365 | } else { |
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366 | (*_flow)[e] = 0; |
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367 | u = _graph.target(e); |
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368 | } |
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369 | } |
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370 | } |
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371 | return _path_num; |
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372 | } |
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373 | |
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374 | /// \brief Compute the paths from the flow. |
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375 | /// |
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376 | /// This function computes the paths from the flow. |
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377 | /// |
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378 | /// \pre \ref init() and \ref findFlow() must be called before using |
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379 | /// this function. |
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380 | void findPaths() { |
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381 | // Create the residual flow map (the union of the paths not found |
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382 | // so far) |
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383 | FlowMap res_flow(_graph); |
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384 | for(ArcIt a(_graph); a != INVALID; ++a) res_flow[a] = (*_flow)[a]; |
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385 | |
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386 | paths.clear(); |
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387 | paths.resize(_path_num); |
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388 | for (int i = 0; i < _path_num; ++i) { |
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389 | Node n = _source; |
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390 | while (n != _target) { |
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391 | OutArcIt e(_graph, n); |
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392 | for ( ; res_flow[e] == 0; ++e) ; |
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393 | n = _graph.target(e); |
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394 | paths[i].addBack(e); |
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395 | res_flow[e] = 0; |
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396 | } |
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397 | } |
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398 | } |
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399 | |
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400 | /// @} |
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401 | |
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402 | /// \name Query Functions |
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403 | /// The results of the algorithm can be obtained using these |
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404 | /// functions. |
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405 | /// \n The algorithm should be executed before using them. |
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406 | |
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407 | /// @{ |
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408 | |
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409 | /// \brief Return a const reference to the arc map storing the |
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410 | /// found flow. |
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411 | /// |
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412 | /// This function returns a const reference to the arc map storing |
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413 | /// the flow that is the union of the found arc-disjoint paths. |
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414 | /// |
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415 | /// \pre \ref run() or \ref findFlow() must be called before using |
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416 | /// this function. |
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417 | const FlowMap& flowMap() const { |
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418 | return *_flow; |
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419 | } |
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420 | |
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421 | /// \brief Return a const reference to the node map storing the |
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422 | /// found potentials (the dual solution). |
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423 | /// |
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424 | /// This function returns a const reference to the node map storing |
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425 | /// the found potentials that provide the dual solution of the |
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426 | /// underlying minimum cost flow problem. |
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427 | /// |
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428 | /// \pre \ref run() or \ref findFlow() must be called before using |
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429 | /// this function. |
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430 | const PotentialMap& potentialMap() const { |
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431 | return *_potential; |
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432 | } |
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433 | |
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434 | /// \brief Return the flow on the given arc. |
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435 | /// |
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436 | /// This function returns the flow on the given arc. |
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437 | /// It is \c 1 if the arc is involved in one of the found paths, |
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438 | /// otherwise it is \c 0. |
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439 | /// |
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440 | /// \pre \ref run() or \ref findFlow() must be called before using |
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441 | /// this function. |
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442 | int flow(const Arc& arc) const { |
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443 | return (*_flow)[arc]; |
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444 | } |
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445 | |
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446 | /// \brief Return the potential of the given node. |
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447 | /// |
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448 | /// This function returns the potential of the given node. |
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449 | /// |
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450 | /// \pre \ref run() or \ref findFlow() must be called before using |
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451 | /// this function. |
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452 | Length potential(const Node& node) const { |
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453 | return (*_potential)[node]; |
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454 | } |
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455 | |
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456 | /// \brief Return the total length (cost) of the found paths (flow). |
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457 | /// |
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458 | /// This function returns the total length (cost) of the found paths |
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459 | /// (flow). The complexity of the function is \f$ O(e) \f$. |
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460 | /// |
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461 | /// \pre \ref run() or \ref findFlow() must be called before using |
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462 | /// this function. |
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463 | Length totalLength() const { |
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464 | Length c = 0; |
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465 | for (ArcIt e(_graph); e != INVALID; ++e) |
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466 | c += (*_flow)[e] * _length[e]; |
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467 | return c; |
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468 | } |
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469 | |
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470 | /// \brief Return the number of the found paths. |
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471 | /// |
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472 | /// This function returns the number of the found paths. |
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473 | /// |
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474 | /// \pre \ref run() or \ref findFlow() must be called before using |
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475 | /// this function. |
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476 | int pathNum() const { |
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477 | return _path_num; |
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478 | } |
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479 | |
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480 | /// \brief Return a const reference to the specified path. |
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481 | /// |
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482 | /// This function returns a const reference to the specified path. |
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483 | /// |
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484 | /// \param i The function returns the \c i-th path. |
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485 | /// \c i must be between \c 0 and <tt>%pathNum()-1</tt>. |
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486 | /// |
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487 | /// \pre \ref run() or \ref findPaths() must be called before using |
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488 | /// this function. |
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489 | Path path(int i) const { |
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490 | return paths[i]; |
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491 | } |
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492 | |
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493 | /// @} |
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494 | |
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495 | }; //class Suurballe |
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496 | |
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497 | ///@} |
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498 | |
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499 | } //namespace lemon |
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500 | |
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501 | #endif //LEMON_SUURBALLE_H |
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