1 | /* -*- C++ -*- |
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2 | * src/lemon/max_matching.h - Part of LEMON, a generic C++ optimization library |
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3 | * |
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4 | * Copyright (C) 2004 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport |
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5 | * (Egervary Combinatorial Optimization Research Group, EGRES). |
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6 | * |
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7 | * Permission to use, modify and distribute this software is granted |
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8 | * provided that this copyright notice appears in all copies. For |
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9 | * precise terms see the accompanying LICENSE file. |
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10 | * |
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11 | * This software is provided "AS IS" with no warranty of any kind, |
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12 | * express or implied, and with no claim as to its suitability for any |
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13 | * purpose. |
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14 | * |
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15 | */ |
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16 | |
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17 | #ifndef LEMON_MAX_MATCHING_H |
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18 | #define LEMON_MAX_MATCHING_H |
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19 | |
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20 | #include <queue> |
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21 | #include <lemon/invalid.h> |
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22 | #include <lemon/unionfind.h> |
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23 | #include <lemon/graph_utils.h> |
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24 | |
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25 | ///\ingroup galgs |
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26 | ///\file |
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27 | ///\brief Maximum matching algorithm. |
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28 | |
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29 | namespace lemon { |
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30 | |
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31 | /// \addtogroup galgs |
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32 | /// @{ |
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33 | |
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34 | ///Edmonds' alternating forest maximum matching algorithm. |
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35 | |
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36 | ///This class provides Edmonds' alternating forest matching |
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37 | ///algorithm. The starting matching (if any) can be passed to the |
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38 | ///algorithm using read-in functions \ref readNMapNode, \ref |
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39 | ///readNMapEdge or \ref readEMapBool depending on the container. The |
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40 | ///resulting maximum matching can be attained by write-out functions |
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41 | ///\ref writeNMapNode, \ref writeNMapEdge or \ref writeEMapBool |
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42 | ///depending on the preferred container. |
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43 | /// |
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44 | ///The dual side of a matching is a map of the nodes to |
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45 | ///MaxMatching::pos_enum, having values D, A and C showing the |
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46 | ///Gallai-Edmonds decomposition of the graph. The nodes in D induce |
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47 | ///a graph with factor-critical components, the nodes in A form the |
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48 | ///barrier, and the nodes in C induce a graph having a perfect |
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49 | ///matching. This decomposition can be attained by calling \ref |
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50 | ///writePos after running the algorithm. |
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51 | /// |
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52 | ///\param Graph The undirected graph type the algorithm runs on. |
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53 | /// |
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54 | ///\author Jacint Szabo |
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55 | template <typename Graph> |
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56 | class MaxMatching { |
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57 | typedef typename Graph::Node Node; |
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58 | typedef typename Graph::Edge Edge; |
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59 | typedef typename Graph::UndirEdgeIt UndirEdgeIt; |
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60 | typedef typename Graph::NodeIt NodeIt; |
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61 | typedef typename Graph::IncEdgeIt IncEdgeIt; |
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62 | |
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63 | typedef UnionFindEnum<Node, Graph::template NodeMap> UFE; |
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64 | |
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65 | public: |
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66 | |
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67 | ///Indicates the Gallai-Edmonds decomposition of the graph. |
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68 | |
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69 | ///Indicates the Gallai-Edmonds decomposition of the graph, which |
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70 | ///shows an upper bound on the size of a maximum matching. The |
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71 | ///nodes with pos_enum \c D induce a graph with factor-critical |
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72 | ///components, the nodes in \c A form the canonical barrier, and the |
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73 | ///nodes in \c C induce a graph having a perfect matching. |
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74 | enum pos_enum { |
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75 | D=0, |
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76 | A=1, |
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77 | C=2 |
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78 | }; |
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79 | |
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80 | private: |
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81 | |
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82 | static const int HEUR_density=2; |
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83 | const Graph& g; |
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84 | typename Graph::template NodeMap<Node> _mate; |
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85 | typename Graph::template NodeMap<pos_enum> position; |
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86 | |
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87 | public: |
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88 | |
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89 | MaxMatching(const Graph& _g) : g(_g), _mate(_g,INVALID), position(_g) {} |
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90 | |
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91 | ///Runs Edmonds' algorithm. |
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92 | |
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93 | ///Runs Edmonds' algorithm for sparse graphs (number of edges < |
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94 | ///2*number of nodes), and a heuristical Edmonds' algorithm with a |
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95 | ///heuristic of postponing shrinks for dense graphs. |
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96 | inline void run(); |
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97 | |
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98 | ///Runs Edmonds' algorithm. |
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99 | |
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100 | ///If heur=0 it runs Edmonds' algorithm. If heur=1 it runs |
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101 | ///Edmonds' algorithm with a heuristic of postponing shrinks, |
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102 | ///giving a faster algorithm for dense graphs. |
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103 | void runEdmonds( int heur ); |
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104 | |
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105 | ///Finds a greedy matching starting from the actual matching. |
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106 | |
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107 | ///Starting form the actual matching stored, it finds a maximal |
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108 | ///greedy matching. |
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109 | void greedyMatching(); |
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110 | |
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111 | ///Returns the size of the actual matching stored. |
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112 | |
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113 | ///Returns the size of the actual matching stored. After \ref |
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114 | ///run() it returns the size of a maximum matching in the graph. |
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115 | int size() const; |
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116 | |
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117 | ///Resets the actual matching to the empty matching. |
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118 | |
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119 | ///Resets the actual matching to the empty matching. |
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120 | /// |
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121 | void resetMatching(); |
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122 | |
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123 | ///Returns the mate of a node in the actual matching. |
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124 | |
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125 | ///Returns the mate of a \c node in the actual matching. |
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126 | ///Returns INVALID if the \c node is not covered by the actual matching. |
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127 | Node mate(Node& node) const { |
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128 | return _mate[node]; |
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129 | } |
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130 | |
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131 | ///Reads a matching from a \c Node map of \c Nodes. |
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132 | |
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133 | ///Reads a matching from a \c Node map of \c Nodes. This map must be \e |
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134 | ///symmetric, i.e. if \c map[u]==v then \c map[v]==u must hold, and |
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135 | ///\c uv will be an edge of the matching. |
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136 | template<typename NMapN> |
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137 | void readNMapNode(NMapN& map) { |
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138 | for(NodeIt v(g); v!=INVALID; ++v) { |
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139 | _mate.set(v,map[v]); |
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140 | } |
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141 | } |
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142 | |
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143 | ///Writes the stored matching to a \c Node map of \c Nodes. |
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144 | |
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145 | ///Writes the stored matching to a \c Node map of \c Nodes. The |
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146 | ///resulting map will be \e symmetric, i.e. if \c map[u]==v then \c |
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147 | ///map[v]==u will hold, and now \c uv is an edge of the matching. |
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148 | template<typename NMapN> |
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149 | void writeNMapNode (NMapN& map) const { |
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150 | for(NodeIt v(g); v!=INVALID; ++v) { |
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151 | map.set(v,_mate[v]); |
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152 | } |
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153 | } |
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154 | |
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155 | ///Reads a matching from a \c Node map of \c Edges. |
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156 | |
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157 | ///Reads a matching from a \c Node map of incident \c Edges. This |
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158 | ///map must have the property that if \c G.target(map[u])==v then \c |
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159 | ///G.target(map[v])==u must hold, and now this edge is an edge of |
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160 | ///the matching. |
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161 | template<typename NMapE> |
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162 | void readNMapEdge(NMapE& map) { |
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163 | for(NodeIt v(g); v!=INVALID; ++v) { |
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164 | Edge e=map[v]; |
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165 | if ( g.valid(e) ) |
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166 | g.source(e) == v ? _mate.set(v,g.target(e)) : _mate.set(v,g.source(e)); |
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167 | } |
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168 | } |
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169 | |
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170 | ///Writes the matching stored to a \c Node map of \c Edges. |
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171 | |
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172 | ///Writes the stored matching to a \c Node map of incident \c |
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173 | ///Edges. This map will have the property that if \c |
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174 | ///g.target(map[u])==v then \c g.target(map[v])==u holds, and now this |
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175 | ///edge is an edge of the matching. |
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176 | template<typename NMapE> |
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177 | void writeNMapEdge (NMapE& map) const { |
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178 | typename Graph::template NodeMap<bool> todo(g,true); |
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179 | for(NodeIt v(g); v!=INVALID; ++v) { |
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180 | if ( todo[v] && _mate[v]!=INVALID ) { |
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181 | Node u=_mate[v]; |
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182 | for(IncEdgeIt e(g,v); e!=INVALID; ++e) { |
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183 | if ( g.target(e) == u ) { |
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184 | map.set(u,e); |
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185 | map.set(v,e); |
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186 | todo.set(u,false); |
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187 | todo.set(v,false); |
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188 | break; |
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189 | } |
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190 | } |
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191 | } |
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192 | } |
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193 | } |
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194 | |
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195 | |
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196 | ///Reads a matching from an \c Edge map of \c bools. |
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197 | |
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198 | ///Reads a matching from an \c Edge map of \c bools. This map must |
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199 | ///have the property that there are no two adjacent edges \c e, \c |
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200 | ///f with \c map[e]==map[f]==true. The edges \c e with \c |
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201 | ///map[e]==true form the matching. |
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202 | template<typename EMapB> |
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203 | void readEMapBool(EMapB& map) { |
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204 | for(UndirEdgeIt e(g); e!=INVALID; ++e) { |
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205 | if ( map[e] ) { |
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206 | Node u=g.source(e); |
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207 | Node v=g.target(e); |
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208 | _mate.set(u,v); |
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209 | _mate.set(v,u); |
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210 | } |
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211 | } |
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212 | } |
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213 | |
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214 | |
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215 | ///Writes the matching stored to an \c Edge map of \c bools. |
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216 | |
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217 | ///Writes the matching stored to an \c Edge map of \c bools. This |
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218 | ///map will have the property that there are no two adjacent edges |
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219 | ///\c e, \c f with \c map[e]==map[f]==true. The edges \c e with \c |
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220 | ///map[e]==true form the matching. |
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221 | template<typename EMapB> |
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222 | void writeEMapBool (EMapB& map) const { |
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223 | for(UndirEdgeIt e(g); e!=INVALID; ++e) map.set(e,false); |
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224 | |
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225 | typename Graph::template NodeMap<bool> todo(g,true); |
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226 | for(NodeIt v(g); v!=INVALID; ++v) { |
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227 | if ( todo[v] && _mate[v]!=INVALID ) { |
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228 | Node u=_mate[v]; |
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229 | for(IncEdgeIt e(g,v); e!=INVALID; ++e) { |
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230 | if ( g.target(e) == u ) { |
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231 | map.set(e,true); |
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232 | todo.set(u,false); |
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233 | todo.set(v,false); |
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234 | break; |
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235 | } |
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236 | } |
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237 | } |
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238 | } |
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239 | } |
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240 | |
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241 | |
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242 | ///Writes the canonical decomposition of the graph after running |
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243 | ///the algorithm. |
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244 | |
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245 | ///After calling any run methods of the class, it writes the |
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246 | ///Gallai-Edmonds canonical decomposition of the graph. \c map |
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247 | ///must be a node map of \ref pos_enum 's. |
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248 | template<typename NMapEnum> |
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249 | void writePos (NMapEnum& map) const { |
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250 | for(NodeIt v(g); v!=INVALID; ++v) map.set(v,position[v]); |
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251 | } |
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252 | |
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253 | private: |
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254 | |
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255 | void lateShrink(Node v, typename Graph::template NodeMap<Node>& ear, |
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256 | UFE& blossom, UFE& tree); |
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257 | |
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258 | void normShrink(Node v, typename Graph::NodeMap<Node>& ear, |
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259 | UFE& blossom, UFE& tree); |
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260 | |
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261 | bool noShrinkStep(Node x, typename Graph::NodeMap<Node>& ear, |
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262 | UFE& blossom, UFE& tree, std::queue<Node>& Q); |
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263 | |
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264 | void shrinkStep(Node& top, Node& middle, Node& bottom, typename Graph::NodeMap<Node>& ear, |
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265 | UFE& blossom, UFE& tree, std::queue<Node>& Q); |
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266 | |
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267 | void augment(Node x, typename Graph::NodeMap<Node>& ear, |
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268 | UFE& blossom, UFE& tree); |
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269 | |
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270 | }; |
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271 | |
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272 | |
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273 | // ********************************************************************** |
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274 | // IMPLEMENTATIONS |
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275 | // ********************************************************************** |
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276 | |
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277 | |
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278 | template <typename Graph> |
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279 | void MaxMatching<Graph>::run() { |
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280 | if ( countUndirEdges(g) < HEUR_density*countNodes(g) ) { |
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281 | greedyMatching(); |
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282 | runEdmonds(0); |
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283 | } else runEdmonds(1); |
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284 | } |
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285 | |
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286 | |
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287 | template <typename Graph> |
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288 | void MaxMatching<Graph>::runEdmonds( int heur=1 ) { |
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289 | |
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290 | for(NodeIt v(g); v!=INVALID; ++v) |
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291 | position.set(v,C); |
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292 | |
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293 | typename Graph::template NodeMap<Node> ear(g,INVALID); |
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294 | //undefined for the base nodes of the blossoms (i.e. for the |
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295 | //representative elements of UFE blossom) and for the nodes in C |
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296 | |
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297 | typename UFE::MapType blossom_base(g); |
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298 | UFE blossom(blossom_base); |
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299 | typename UFE::MapType tree_base(g); |
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300 | UFE tree(tree_base); |
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301 | |
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302 | for(NodeIt v(g); v!=INVALID; ++v) { |
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303 | if ( position[v]==C && _mate[v]==INVALID ) { |
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304 | blossom.insert(v); |
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305 | tree.insert(v); |
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306 | position.set(v,D); |
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307 | if ( heur == 1 ) lateShrink( v, ear, blossom, tree ); |
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308 | else normShrink( v, ear, blossom, tree ); |
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309 | } |
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310 | } |
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311 | } |
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312 | |
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313 | |
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314 | template <typename Graph> |
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315 | void MaxMatching<Graph>::lateShrink(Node v, typename Graph::template NodeMap<Node>& ear, |
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316 | UFE& blossom, UFE& tree) { |
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317 | |
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318 | std::queue<Node> Q; //queue of the totally unscanned nodes |
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319 | Q.push(v); |
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320 | std::queue<Node> R; |
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321 | //queue of the nodes which must be scanned for a possible shrink |
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322 | |
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323 | while ( !Q.empty() ) { |
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324 | Node x=Q.front(); |
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325 | Q.pop(); |
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326 | if ( noShrinkStep( x, ear, blossom, tree, Q ) ) return; |
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327 | else R.push(x); |
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328 | } |
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329 | |
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330 | while ( !R.empty() ) { |
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331 | Node x=R.front(); |
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332 | R.pop(); |
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333 | |
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334 | for( IncEdgeIt e(g,x); e!=INVALID ; ++e ) { |
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335 | Node y=g.target(e); |
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336 | |
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337 | if ( position[y] == D && blossom.find(x) != blossom.find(y) ) { |
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338 | //x and y must be in the same tree |
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339 | |
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340 | typename Graph::template NodeMap<bool> path(g,false); |
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341 | |
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342 | Node b=blossom.find(x); |
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343 | path.set(b,true); |
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344 | b=_mate[b]; |
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345 | while ( b!=INVALID ) { |
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346 | b=blossom.find(ear[b]); |
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347 | path.set(b,true); |
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348 | b=_mate[b]; |
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349 | } //going till the root |
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350 | |
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351 | Node top=y; |
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352 | Node middle=blossom.find(top); |
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353 | Node bottom=x; |
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354 | while ( !path[middle] ) |
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355 | shrinkStep(top, middle, bottom, ear, blossom, tree, Q); |
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356 | |
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357 | Node base=middle; |
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358 | top=x; |
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359 | middle=blossom.find(top); |
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360 | bottom=y; |
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361 | Node blossom_base=blossom.find(base); |
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362 | while ( middle!=blossom_base ) |
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363 | shrinkStep(top, middle, bottom, ear, blossom, tree, Q); |
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364 | |
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365 | blossom.makeRep(base); |
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366 | } // if shrink is needed |
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367 | |
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368 | while ( !Q.empty() ) { |
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369 | Node x=Q.front(); |
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370 | Q.pop(); |
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371 | if ( noShrinkStep(x, ear, blossom, tree, Q) ) return; |
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372 | else R.push(x); |
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373 | } |
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374 | } //for e |
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375 | } // while ( !R.empty() ) |
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376 | } |
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377 | |
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378 | |
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379 | template <typename Graph> |
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380 | void MaxMatching<Graph>::normShrink(Node v, typename Graph::NodeMap<Node>& ear, |
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381 | UFE& blossom, UFE& tree) { |
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382 | |
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383 | std::queue<Node> Q; //queue of the unscanned nodes |
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384 | Q.push(v); |
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385 | while ( !Q.empty() ) { |
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386 | |
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387 | Node x=Q.front(); |
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388 | Q.pop(); |
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389 | |
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390 | for( IncEdgeIt e(g,x); e!=INVALID; ++e ) { |
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391 | Node y=g.target(e); |
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392 | |
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393 | switch ( position[y] ) { |
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394 | case D: //x and y must be in the same tree |
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395 | |
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396 | if ( blossom.find(x) != blossom.find(y) ) { //shrink |
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397 | typename Graph::template NodeMap<bool> path(g,false); |
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398 | |
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399 | Node b=blossom.find(x); |
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400 | path.set(b,true); |
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401 | b=_mate[b]; |
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402 | while ( b!=INVALID ) { |
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403 | b=blossom.find(ear[b]); |
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404 | path.set(b,true); |
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405 | b=_mate[b]; |
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406 | } //going till the root |
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407 | |
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408 | Node top=y; |
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409 | Node middle=blossom.find(top); |
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410 | Node bottom=x; |
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411 | while ( !path[middle] ) |
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412 | shrinkStep(top, middle, bottom, ear, blossom, tree, Q); |
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413 | |
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414 | Node base=middle; |
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415 | top=x; |
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416 | middle=blossom.find(top); |
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417 | bottom=y; |
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418 | Node blossom_base=blossom.find(base); |
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419 | while ( middle!=blossom_base ) |
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420 | shrinkStep(top, middle, bottom, ear, blossom, tree, Q); |
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421 | |
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422 | blossom.makeRep(base); |
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423 | } |
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424 | break; |
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425 | case C: |
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426 | if ( _mate[y]!=INVALID ) { //grow |
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427 | |
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428 | ear.set(y,x); |
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429 | Node w=_mate[y]; |
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430 | blossom.insert(w); |
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431 | position.set(y,A); |
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432 | position.set(w,D); |
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433 | tree.insert(y); |
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434 | tree.insert(w); |
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435 | tree.join(y,blossom.find(x)); |
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436 | tree.join(w,y); |
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437 | Q.push(w); |
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438 | } else { //augment |
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439 | augment(x, ear, blossom, tree); |
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440 | _mate.set(x,y); |
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441 | _mate.set(y,x); |
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442 | return; |
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443 | } //if |
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444 | break; |
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445 | default: break; |
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446 | } |
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447 | } |
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448 | } |
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449 | } |
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450 | |
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451 | template <typename Graph> |
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452 | void MaxMatching<Graph>::greedyMatching() { |
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453 | for(NodeIt v(g); v!=INVALID; ++v) |
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454 | if ( _mate[v]==INVALID ) { |
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455 | for( IncEdgeIt e(g,v); e!=INVALID ; ++e ) { |
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456 | Node y=g.target(e); |
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457 | if ( _mate[y]==INVALID && y!=v ) { |
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458 | _mate.set(v,y); |
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459 | _mate.set(y,v); |
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460 | break; |
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461 | } |
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462 | } |
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463 | } |
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464 | } |
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465 | |
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466 | template <typename Graph> |
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467 | int MaxMatching<Graph>::size() const { |
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468 | int s=0; |
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469 | for(NodeIt v(g); v!=INVALID; ++v) { |
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470 | if ( _mate[v]!=INVALID ) { |
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471 | ++s; |
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472 | } |
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473 | } |
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474 | return (int)s/2; |
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475 | } |
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476 | |
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477 | template <typename Graph> |
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478 | void MaxMatching<Graph>::resetMatching() { |
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479 | for(NodeIt v(g); v!=INVALID; ++v) |
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480 | _mate.set(v,INVALID); |
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481 | } |
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482 | |
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483 | template <typename Graph> |
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484 | bool MaxMatching<Graph>::noShrinkStep(Node x, typename Graph::NodeMap<Node>& ear, |
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485 | UFE& blossom, UFE& tree, std::queue<Node>& Q) { |
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486 | for( IncEdgeIt e(g,x); e!= INVALID; ++e ) { |
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487 | Node y=g.target(e); |
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488 | |
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489 | if ( position[y]==C ) { |
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490 | if ( _mate[y]!=INVALID ) { //grow |
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491 | ear.set(y,x); |
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492 | Node w=_mate[y]; |
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493 | blossom.insert(w); |
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494 | position.set(y,A); |
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495 | position.set(w,D); |
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496 | tree.insert(y); |
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497 | tree.insert(w); |
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498 | tree.join(y,blossom.find(x)); |
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499 | tree.join(w,y); |
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500 | Q.push(w); |
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501 | } else { //augment |
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502 | augment(x, ear, blossom, tree); |
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503 | _mate.set(x,y); |
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504 | _mate.set(y,x); |
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505 | return true; |
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506 | } |
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507 | } |
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508 | } |
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509 | return false; |
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510 | } |
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511 | |
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512 | template <typename Graph> |
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513 | void MaxMatching<Graph>::shrinkStep(Node& top, Node& middle, Node& bottom, typename Graph::NodeMap<Node>& ear, |
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514 | UFE& blossom, UFE& tree, std::queue<Node>& Q) { |
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515 | ear.set(top,bottom); |
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516 | Node t=top; |
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517 | while ( t!=middle ) { |
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518 | Node u=_mate[t]; |
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519 | t=ear[u]; |
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520 | ear.set(t,u); |
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521 | } |
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522 | bottom=_mate[middle]; |
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523 | position.set(bottom,D); |
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524 | Q.push(bottom); |
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525 | top=ear[bottom]; |
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526 | Node oldmiddle=middle; |
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527 | middle=blossom.find(top); |
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528 | tree.erase(bottom); |
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529 | tree.erase(oldmiddle); |
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530 | blossom.insert(bottom); |
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531 | blossom.join(bottom, oldmiddle); |
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532 | blossom.join(top, oldmiddle); |
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533 | } |
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534 | |
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535 | template <typename Graph> |
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536 | void MaxMatching<Graph>::augment(Node x, typename Graph::NodeMap<Node>& ear, |
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537 | UFE& blossom, UFE& tree) { |
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538 | Node v=_mate[x]; |
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539 | while ( v!=INVALID ) { |
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540 | |
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541 | Node u=ear[v]; |
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542 | _mate.set(v,u); |
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543 | Node tmp=v; |
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544 | v=_mate[u]; |
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545 | _mate.set(u,tmp); |
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546 | } |
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547 | typename UFE::ItemIt it; |
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548 | for (tree.first(it,blossom.find(x)); tree.valid(it); tree.next(it)) { |
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549 | if ( position[it] == D ) { |
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550 | typename UFE::ItemIt b_it; |
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551 | for (blossom.first(b_it,it); blossom.valid(b_it); blossom.next(b_it)) { |
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552 | position.set( b_it ,C); |
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553 | } |
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554 | blossom.eraseClass(it); |
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555 | } else position.set( it ,C); |
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556 | } |
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557 | tree.eraseClass(x); |
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558 | |
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559 | } |
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560 | |
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561 | /// @} |
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562 | |
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563 | } //END OF NAMESPACE LEMON |
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564 | |
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565 | #endif //EDMONDS_H |
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