1 | /* -*- C++ -*- |
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2 | * lemon/preflow.h - Part of LEMON, a generic C++ optimization library |
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3 | * |
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4 | * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport |
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5 | * (Egervary Research Group on Combinatorial Optimization, 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_PREFLOW_H |
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18 | #define LEMON_PREFLOW_H |
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19 | |
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20 | #include <vector> |
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21 | #include <queue> |
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22 | |
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23 | #include <lemon/invalid.h> |
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24 | #include <lemon/maps.h> |
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25 | #include <lemon/graph_utils.h> |
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26 | |
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27 | /// \file |
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28 | /// \ingroup flowalgs |
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29 | /// \brief Implementation of the preflow algorithm. |
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30 | |
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31 | namespace lemon { |
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32 | |
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33 | /// \addtogroup flowalgs |
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34 | /// @{ |
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35 | |
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36 | ///%Preflow algorithms class. |
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37 | |
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38 | ///This class provides an implementation of the \e preflow \e |
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39 | ///algorithm producing a flow of maximum value in a directed |
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40 | ///graph. The preflow algorithms are the fastest known max flow algorithms |
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41 | ///up to now. The \e source node, the \e target node, the \e |
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42 | ///capacity of the edges and the \e starting \e flow value of the |
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43 | ///edges should be passed to the algorithm through the |
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44 | ///constructor. It is possible to change these quantities using the |
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45 | ///functions \ref source, \ref target, \ref capacityMap and \ref |
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46 | ///flowMap. |
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47 | /// |
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48 | ///After running \ref lemon::Preflow::phase1() "phase1()" |
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49 | ///or \ref lemon::Preflow::run() "run()", the maximal flow |
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50 | ///value can be obtained by calling \ref flowValue(). The minimum |
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51 | ///value cut can be written into a <tt>bool</tt> node map by |
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52 | ///calling \ref minCut(). (\ref minMinCut() and \ref maxMinCut() writes |
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53 | ///the inclusionwise minimum and maximum of the minimum value cuts, |
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54 | ///resp.) |
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55 | /// |
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56 | ///\param Graph The directed graph type the algorithm runs on. |
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57 | ///\param Num The number type of the capacities and the flow values. |
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58 | ///\param CapacityMap The capacity map type. |
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59 | ///\param FlowMap The flow map type. |
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60 | /// |
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61 | ///\author Jacint Szabo |
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62 | ///\todo Second template parameter is superfluous |
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63 | template <typename Graph, typename Num, |
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64 | typename CapacityMap=typename Graph::template EdgeMap<Num>, |
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65 | typename FlowMap=typename Graph::template EdgeMap<Num> > |
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66 | class Preflow { |
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67 | protected: |
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68 | typedef typename Graph::Node Node; |
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69 | typedef typename Graph::NodeIt NodeIt; |
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70 | typedef typename Graph::EdgeIt EdgeIt; |
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71 | typedef typename Graph::OutEdgeIt OutEdgeIt; |
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72 | typedef typename Graph::InEdgeIt InEdgeIt; |
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73 | |
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74 | typedef typename Graph::template NodeMap<Node> NNMap; |
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75 | typedef typename std::vector<Node> VecNode; |
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76 | |
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77 | const Graph* _g; |
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78 | Node _source; |
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79 | Node _target; |
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80 | const CapacityMap* _capacity; |
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81 | FlowMap* _flow; |
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82 | int _node_num; //the number of nodes of G |
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83 | |
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84 | typename Graph::template NodeMap<int> level; |
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85 | typename Graph::template NodeMap<Num> excess; |
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86 | |
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87 | // constants used for heuristics |
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88 | static const int H0=20; |
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89 | static const int H1=1; |
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90 | |
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91 | public: |
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92 | |
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93 | ///Indicates the property of the starting flow map. |
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94 | |
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95 | ///Indicates the property of the starting flow map. |
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96 | ///The meanings are as follows: |
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97 | ///- \c ZERO_FLOW: constant zero flow |
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98 | ///- \c GEN_FLOW: any flow, i.e. the sum of the in-flows equals to |
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99 | ///the sum of the out-flows in every node except the \e source and |
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100 | ///the \e target. |
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101 | ///- \c PRE_FLOW: any preflow, i.e. the sum of the in-flows is at |
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102 | ///least the sum of the out-flows in every node except the \e source. |
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103 | ///- \c NO_FLOW: indicates an unspecified edge map. \c flow will be |
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104 | ///set to the constant zero flow in the beginning of |
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105 | ///the algorithm in this case. |
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106 | /// |
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107 | enum FlowEnum{ |
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108 | NO_FLOW, |
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109 | ZERO_FLOW, |
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110 | GEN_FLOW, |
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111 | PRE_FLOW |
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112 | }; |
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113 | |
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114 | ///Indicates the state of the preflow algorithm. |
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115 | |
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116 | ///Indicates the state of the preflow algorithm. |
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117 | ///The meanings are as follows: |
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118 | ///- \c AFTER_NOTHING: before running the algorithm or |
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119 | /// at an unspecified state. |
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120 | ///- \c AFTER_PREFLOW_PHASE_1: right after running \c phase1 |
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121 | ///- \c AFTER_PREFLOW_PHASE_2: after running \ref phase2() |
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122 | /// |
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123 | enum StatusEnum { |
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124 | AFTER_NOTHING, |
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125 | AFTER_PREFLOW_PHASE_1, |
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126 | AFTER_PREFLOW_PHASE_2 |
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127 | }; |
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128 | |
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129 | protected: |
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130 | FlowEnum flow_prop; |
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131 | StatusEnum status; // Do not needle this flag only if necessary. |
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132 | |
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133 | public: |
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134 | ///The constructor of the class. |
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135 | |
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136 | ///The constructor of the class. |
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137 | ///\param _gr The directed graph the algorithm runs on. |
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138 | ///\param _s The source node. |
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139 | ///\param _t The target node. |
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140 | ///\param _cap The capacity of the edges. |
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141 | ///\param _f The flow of the edges. |
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142 | ///Except the graph, all of these parameters can be reset by |
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143 | ///calling \ref source, \ref target, \ref capacityMap and \ref |
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144 | ///flowMap, resp. |
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145 | Preflow(const Graph& _gr, Node _s, Node _t, |
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146 | const CapacityMap& _cap, FlowMap& _f) : |
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147 | _g(&_gr), _source(_s), _target(_t), _capacity(&_cap), |
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148 | _flow(&_f), _node_num(countNodes(_gr)), level(_gr), excess(_gr,0), |
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149 | flow_prop(NO_FLOW), status(AFTER_NOTHING) { } |
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150 | |
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151 | |
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152 | |
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153 | ///Runs the preflow algorithm. |
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154 | |
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155 | ///Runs the preflow algorithm. |
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156 | /// |
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157 | void run() { |
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158 | phase1(flow_prop); |
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159 | phase2(); |
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160 | } |
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161 | |
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162 | ///Runs the preflow algorithm. |
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163 | |
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164 | ///Runs the preflow algorithm. |
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165 | ///\pre The starting flow map must be |
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166 | /// - a constant zero flow if \c fp is \c ZERO_FLOW, |
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167 | /// - an arbitrary flow if \c fp is \c GEN_FLOW, |
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168 | /// - an arbitrary preflow if \c fp is \c PRE_FLOW, |
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169 | /// - any map if \c fp is NO_FLOW. |
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170 | ///If the starting flow map is a flow or a preflow then |
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171 | ///the algorithm terminates faster. |
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172 | void run(FlowEnum fp) { |
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173 | flow_prop=fp; |
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174 | run(); |
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175 | } |
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176 | |
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177 | ///Runs the first phase of the preflow algorithm. |
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178 | |
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179 | ///The preflow algorithm consists of two phases, this method runs |
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180 | ///the first phase. After the first phase the maximum flow value |
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181 | ///and a minimum value cut can already be computed, although a |
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182 | ///maximum flow is not yet obtained. So after calling this method |
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183 | ///\ref flowValue returns the value of a maximum flow and \ref |
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184 | ///minCut returns a minimum cut. |
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185 | ///\warning \ref minMinCut and \ref maxMinCut do not give minimum |
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186 | ///value cuts unless calling \ref phase2. |
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187 | ///\pre The starting flow must be |
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188 | ///- a constant zero flow if \c fp is \c ZERO_FLOW, |
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189 | ///- an arbitary flow if \c fp is \c GEN_FLOW, |
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190 | ///- an arbitary preflow if \c fp is \c PRE_FLOW, |
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191 | ///- any map if \c fp is NO_FLOW. |
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192 | void phase1(FlowEnum fp) |
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193 | { |
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194 | flow_prop=fp; |
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195 | phase1(); |
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196 | } |
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197 | |
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198 | |
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199 | ///Runs the first phase of the preflow algorithm. |
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200 | |
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201 | ///The preflow algorithm consists of two phases, this method runs |
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202 | ///the first phase. After the first phase the maximum flow value |
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203 | ///and a minimum value cut can already be computed, although a |
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204 | ///maximum flow is not yet obtained. So after calling this method |
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205 | ///\ref flowValue returns the value of a maximum flow and \ref |
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206 | ///minCut returns a minimum cut. |
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207 | ///\warning \ref minCut(), \ref minMinCut() and \ref maxMinCut() do not |
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208 | ///give minimum value cuts unless calling \ref phase2(). |
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209 | void phase1() |
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210 | { |
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211 | int heur0=(int)(H0*_node_num); //time while running 'bound decrease' |
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212 | int heur1=(int)(H1*_node_num); //time while running 'highest label' |
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213 | int heur=heur1; //starting time interval (#of relabels) |
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214 | int numrelabel=0; |
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215 | |
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216 | bool what_heur=1; |
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217 | //It is 0 in case 'bound decrease' and 1 in case 'highest label' |
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218 | |
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219 | bool end=false; |
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220 | //Needed for 'bound decrease', true means no active |
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221 | //nodes are above bound b. |
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222 | |
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223 | int k=_node_num-2; //bound on the highest level under n containing a node |
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224 | int b=k; //bound on the highest level under n of an active node |
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225 | |
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226 | VecNode first(_node_num, INVALID); |
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227 | NNMap next(*_g, INVALID); |
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228 | |
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229 | NNMap left(*_g, INVALID); |
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230 | NNMap right(*_g, INVALID); |
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231 | VecNode level_list(_node_num,INVALID); |
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232 | //List of the nodes in level i<n, set to n. |
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233 | |
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234 | preflowPreproc(first, next, level_list, left, right); |
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235 | |
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236 | //Push/relabel on the highest level active nodes. |
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237 | while ( true ) { |
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238 | if ( b == 0 ) { |
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239 | if ( !what_heur && !end && k > 0 ) { |
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240 | b=k; |
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241 | end=true; |
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242 | } else break; |
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243 | } |
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244 | |
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245 | if ( first[b]==INVALID ) --b; |
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246 | else { |
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247 | end=false; |
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248 | Node w=first[b]; |
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249 | first[b]=next[w]; |
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250 | int newlevel=push(w, next, first); |
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251 | if ( excess[w] > 0 ) relabel(w, newlevel, first, next, level_list, |
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252 | left, right, b, k, what_heur); |
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253 | |
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254 | ++numrelabel; |
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255 | if ( numrelabel >= heur ) { |
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256 | numrelabel=0; |
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257 | if ( what_heur ) { |
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258 | what_heur=0; |
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259 | heur=heur0; |
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260 | end=false; |
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261 | } else { |
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262 | what_heur=1; |
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263 | heur=heur1; |
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264 | b=k; |
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265 | } |
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266 | } |
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267 | } |
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268 | } |
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269 | flow_prop=PRE_FLOW; |
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270 | status=AFTER_PREFLOW_PHASE_1; |
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271 | } |
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272 | // Heuristics: |
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273 | // 2 phase |
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274 | // gap |
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275 | // list 'level_list' on the nodes on level i implemented by hand |
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276 | // stack 'active' on the active nodes on level i |
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277 | // runs heuristic 'highest label' for H1*n relabels |
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278 | // runs heuristic 'bound decrease' for H0*n relabels, |
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279 | // starts with 'highest label' |
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280 | // Parameters H0 and H1 are initialized to 20 and 1. |
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281 | |
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282 | |
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283 | ///Runs the second phase of the preflow algorithm. |
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284 | |
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285 | ///The preflow algorithm consists of two phases, this method runs |
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286 | ///the second phase. After calling \ref phase1() and then |
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287 | ///\ref phase2(), |
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288 | /// \ref flowMap() return a maximum flow, \ref flowValue |
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289 | ///returns the value of a maximum flow, \ref minCut returns a |
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290 | ///minimum cut, while the methods \ref minMinCut and \ref |
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291 | ///maxMinCut return the inclusionwise minimum and maximum cuts of |
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292 | ///minimum value, resp. \pre \ref phase1 must be called before. |
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293 | void phase2() |
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294 | { |
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295 | |
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296 | int k=_node_num-2; //bound on the highest level under n containing a node |
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297 | int b=k; //bound on the highest level under n of an active node |
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298 | |
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299 | |
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300 | VecNode first(_node_num, INVALID); |
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301 | NNMap next(*_g, INVALID); |
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302 | level.set(_source,0); |
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303 | std::queue<Node> bfs_queue; |
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304 | bfs_queue.push(_source); |
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305 | |
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306 | while ( !bfs_queue.empty() ) { |
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307 | |
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308 | Node v=bfs_queue.front(); |
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309 | bfs_queue.pop(); |
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310 | int l=level[v]+1; |
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311 | |
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312 | for(InEdgeIt e(*_g,v); e!=INVALID; ++e) { |
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313 | if ( (*_capacity)[e] <= (*_flow)[e] ) continue; |
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314 | Node u=_g->source(e); |
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315 | if ( level[u] >= _node_num ) { |
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316 | bfs_queue.push(u); |
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317 | level.set(u, l); |
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318 | if ( excess[u] > 0 ) { |
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319 | next.set(u,first[l]); |
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320 | first[l]=u; |
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321 | } |
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322 | } |
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323 | } |
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324 | |
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325 | for(OutEdgeIt e(*_g,v); e!=INVALID; ++e) { |
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326 | if ( 0 >= (*_flow)[e] ) continue; |
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327 | Node u=_g->target(e); |
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328 | if ( level[u] >= _node_num ) { |
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329 | bfs_queue.push(u); |
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330 | level.set(u, l); |
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331 | if ( excess[u] > 0 ) { |
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332 | next.set(u,first[l]); |
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333 | first[l]=u; |
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334 | } |
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335 | } |
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336 | } |
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337 | } |
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338 | b=_node_num-2; |
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339 | |
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340 | while ( true ) { |
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341 | |
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342 | if ( b == 0 ) break; |
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343 | if ( first[b]==INVALID ) --b; |
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344 | else { |
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345 | Node w=first[b]; |
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346 | first[b]=next[w]; |
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347 | int newlevel=push(w,next, first); |
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348 | |
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349 | //relabel |
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350 | if ( excess[w] > 0 ) { |
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351 | level.set(w,++newlevel); |
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352 | next.set(w,first[newlevel]); |
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353 | first[newlevel]=w; |
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354 | b=newlevel; |
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355 | } |
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356 | } |
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357 | } // while(true) |
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358 | flow_prop=GEN_FLOW; |
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359 | status=AFTER_PREFLOW_PHASE_2; |
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360 | } |
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361 | |
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362 | /// Returns the value of the maximum flow. |
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363 | |
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364 | /// Returns the value of the maximum flow by returning the excess |
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365 | /// of the target node \c t. This value equals to the value of |
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366 | /// the maximum flow already after running \ref phase1. |
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367 | Num flowValue() const { |
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368 | return excess[_target]; |
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369 | } |
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370 | |
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371 | |
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372 | ///Returns a minimum value cut. |
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373 | |
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374 | ///Sets \c M to the characteristic vector of a minimum value |
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375 | ///cut. This method can be called both after running \ref |
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376 | ///phase1 and \ref phase2. It is much faster after |
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377 | ///\ref phase1. \pre M should be a bool-valued node-map. \pre |
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378 | ///If \ref minCut() is called after \ref phase2() then M should |
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379 | ///be initialized to false. |
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380 | template<typename _CutMap> |
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381 | void minCut(_CutMap& M) const { |
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382 | switch ( status ) { |
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383 | case AFTER_PREFLOW_PHASE_1: |
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384 | for(NodeIt v(*_g); v!=INVALID; ++v) { |
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385 | if (level[v] < _node_num) { |
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386 | M.set(v, false); |
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387 | } else { |
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388 | M.set(v, true); |
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389 | } |
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390 | } |
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391 | break; |
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392 | case AFTER_PREFLOW_PHASE_2: |
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393 | minMinCut(M); |
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394 | break; |
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395 | case AFTER_NOTHING: |
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396 | break; |
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397 | } |
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398 | } |
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399 | |
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400 | ///Returns the inclusionwise minimum of the minimum value cuts. |
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401 | |
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402 | ///Sets \c M to the characteristic vector of the minimum value cut |
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403 | ///which is inclusionwise minimum. It is computed by processing a |
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404 | ///bfs from the source node \c s in the residual graph. \pre M |
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405 | ///should be a node map of bools initialized to false. \pre \ref |
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406 | ///phase2 should already be run. |
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407 | template<typename _CutMap> |
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408 | void minMinCut(_CutMap& M) const { |
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409 | |
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410 | std::queue<Node> queue; |
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411 | M.set(_source,true); |
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412 | queue.push(_source); |
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413 | |
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414 | while (!queue.empty()) { |
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415 | Node w=queue.front(); |
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416 | queue.pop(); |
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417 | |
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418 | for(OutEdgeIt e(*_g,w) ; e!=INVALID; ++e) { |
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419 | Node v=_g->target(e); |
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420 | if (!M[v] && (*_flow)[e] < (*_capacity)[e] ) { |
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421 | queue.push(v); |
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422 | M.set(v, true); |
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423 | } |
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424 | } |
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425 | |
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426 | for(InEdgeIt e(*_g,w) ; e!=INVALID; ++e) { |
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427 | Node v=_g->source(e); |
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428 | if (!M[v] && (*_flow)[e] > 0 ) { |
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429 | queue.push(v); |
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430 | M.set(v, true); |
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431 | } |
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432 | } |
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433 | } |
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434 | } |
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435 | |
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436 | ///Returns the inclusionwise maximum of the minimum value cuts. |
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437 | |
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438 | ///Sets \c M to the characteristic vector of the minimum value cut |
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439 | ///which is inclusionwise maximum. It is computed by processing a |
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440 | ///backward bfs from the target node \c t in the residual graph. |
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441 | ///\pre \ref phase2() or run() should already be run. |
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442 | template<typename _CutMap> |
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443 | void maxMinCut(_CutMap& M) const { |
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444 | |
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445 | for(NodeIt v(*_g) ; v!=INVALID; ++v) M.set(v, true); |
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446 | |
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447 | std::queue<Node> queue; |
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448 | |
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449 | M.set(_target,false); |
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450 | queue.push(_target); |
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451 | |
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452 | while (!queue.empty()) { |
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453 | Node w=queue.front(); |
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454 | queue.pop(); |
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455 | |
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456 | for(InEdgeIt e(*_g,w) ; e!=INVALID; ++e) { |
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457 | Node v=_g->source(e); |
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458 | if (M[v] && (*_flow)[e] < (*_capacity)[e] ) { |
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459 | queue.push(v); |
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460 | M.set(v, false); |
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461 | } |
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462 | } |
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463 | |
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464 | for(OutEdgeIt e(*_g,w) ; e!=INVALID; ++e) { |
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465 | Node v=_g->target(e); |
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466 | if (M[v] && (*_flow)[e] > 0 ) { |
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467 | queue.push(v); |
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468 | M.set(v, false); |
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469 | } |
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470 | } |
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471 | } |
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472 | } |
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473 | |
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474 | ///Sets the source node to \c _s. |
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475 | |
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476 | ///Sets the source node to \c _s. |
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477 | /// |
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478 | void source(Node _s) { |
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479 | _source=_s; |
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480 | if ( flow_prop != ZERO_FLOW ) flow_prop=NO_FLOW; |
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481 | status=AFTER_NOTHING; |
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482 | } |
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483 | |
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484 | ///Returns the source node. |
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485 | |
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486 | ///Returns the source node. |
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487 | /// |
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488 | Node source() const { |
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489 | return _source; |
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490 | } |
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491 | |
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492 | ///Sets the target node to \c _t. |
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493 | |
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494 | ///Sets the target node to \c _t. |
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495 | /// |
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496 | void target(Node _t) { |
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497 | _target=_t; |
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498 | if ( flow_prop == GEN_FLOW ) flow_prop=PRE_FLOW; |
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499 | status=AFTER_NOTHING; |
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500 | } |
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501 | |
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502 | ///Returns the target node. |
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503 | |
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504 | ///Returns the target node. |
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505 | /// |
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506 | Node target() const { |
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507 | return _target; |
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508 | } |
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509 | |
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510 | /// Sets the edge map of the capacities to _cap. |
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511 | |
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512 | /// Sets the edge map of the capacities to _cap. |
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513 | /// |
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514 | void capacityMap(const CapacityMap& _cap) { |
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515 | _capacity=&_cap; |
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516 | status=AFTER_NOTHING; |
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517 | } |
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518 | /// Returns a reference to capacity map. |
---|
519 | |
---|
520 | /// Returns a reference to capacity map. |
---|
521 | /// |
---|
522 | const CapacityMap &capacityMap() const { |
---|
523 | return *_capacity; |
---|
524 | } |
---|
525 | |
---|
526 | /// Sets the edge map of the flows to _flow. |
---|
527 | |
---|
528 | /// Sets the edge map of the flows to _flow. |
---|
529 | /// |
---|
530 | void flowMap(FlowMap& _f) { |
---|
531 | _flow=&_f; |
---|
532 | flow_prop=NO_FLOW; |
---|
533 | status=AFTER_NOTHING; |
---|
534 | } |
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535 | |
---|
536 | /// Returns a reference to flow map. |
---|
537 | |
---|
538 | /// Returns a reference to flow map. |
---|
539 | /// |
---|
540 | const FlowMap &flowMap() const { |
---|
541 | return *_flow; |
---|
542 | } |
---|
543 | |
---|
544 | private: |
---|
545 | |
---|
546 | int push(Node w, NNMap& next, VecNode& first) { |
---|
547 | |
---|
548 | int lev=level[w]; |
---|
549 | Num exc=excess[w]; |
---|
550 | int newlevel=_node_num; //bound on the next level of w |
---|
551 | |
---|
552 | for(OutEdgeIt e(*_g,w) ; e!=INVALID; ++e) { |
---|
553 | if ( (*_flow)[e] >= (*_capacity)[e] ) continue; |
---|
554 | Node v=_g->target(e); |
---|
555 | |
---|
556 | if( lev > level[v] ) { //Push is allowed now |
---|
557 | |
---|
558 | if ( excess[v]<=0 && v!=_target && v!=_source ) { |
---|
559 | next.set(v,first[level[v]]); |
---|
560 | first[level[v]]=v; |
---|
561 | } |
---|
562 | |
---|
563 | Num cap=(*_capacity)[e]; |
---|
564 | Num flo=(*_flow)[e]; |
---|
565 | Num remcap=cap-flo; |
---|
566 | |
---|
567 | if ( remcap >= exc ) { //A nonsaturating push. |
---|
568 | |
---|
569 | _flow->set(e, flo+exc); |
---|
570 | excess.set(v, excess[v]+exc); |
---|
571 | exc=0; |
---|
572 | break; |
---|
573 | |
---|
574 | } else { //A saturating push. |
---|
575 | _flow->set(e, cap); |
---|
576 | excess.set(v, excess[v]+remcap); |
---|
577 | exc-=remcap; |
---|
578 | } |
---|
579 | } else if ( newlevel > level[v] ) newlevel = level[v]; |
---|
580 | } //for out edges wv |
---|
581 | |
---|
582 | if ( exc > 0 ) { |
---|
583 | for(InEdgeIt e(*_g,w) ; e!=INVALID; ++e) { |
---|
584 | |
---|
585 | if( (*_flow)[e] <= 0 ) continue; |
---|
586 | Node v=_g->source(e); |
---|
587 | |
---|
588 | if( lev > level[v] ) { //Push is allowed now |
---|
589 | |
---|
590 | if ( excess[v]<=0 && v!=_target && v!=_source ) { |
---|
591 | next.set(v,first[level[v]]); |
---|
592 | first[level[v]]=v; |
---|
593 | } |
---|
594 | |
---|
595 | Num flo=(*_flow)[e]; |
---|
596 | |
---|
597 | if ( flo >= exc ) { //A nonsaturating push. |
---|
598 | |
---|
599 | _flow->set(e, flo-exc); |
---|
600 | excess.set(v, excess[v]+exc); |
---|
601 | exc=0; |
---|
602 | break; |
---|
603 | } else { //A saturating push. |
---|
604 | |
---|
605 | excess.set(v, excess[v]+flo); |
---|
606 | exc-=flo; |
---|
607 | _flow->set(e,0); |
---|
608 | } |
---|
609 | } else if ( newlevel > level[v] ) newlevel = level[v]; |
---|
610 | } //for in edges vw |
---|
611 | |
---|
612 | } // if w still has excess after the out edge for cycle |
---|
613 | |
---|
614 | excess.set(w, exc); |
---|
615 | |
---|
616 | return newlevel; |
---|
617 | } |
---|
618 | |
---|
619 | |
---|
620 | |
---|
621 | void preflowPreproc(VecNode& first, NNMap& next, |
---|
622 | VecNode& level_list, NNMap& left, NNMap& right) |
---|
623 | { |
---|
624 | for(NodeIt v(*_g); v!=INVALID; ++v) level.set(v,_node_num); |
---|
625 | std::queue<Node> bfs_queue; |
---|
626 | |
---|
627 | if ( flow_prop == GEN_FLOW || flow_prop == PRE_FLOW ) { |
---|
628 | //Reverse_bfs from t in the residual graph, |
---|
629 | //to find the starting level. |
---|
630 | level.set(_target,0); |
---|
631 | bfs_queue.push(_target); |
---|
632 | |
---|
633 | while ( !bfs_queue.empty() ) { |
---|
634 | |
---|
635 | Node v=bfs_queue.front(); |
---|
636 | bfs_queue.pop(); |
---|
637 | int l=level[v]+1; |
---|
638 | |
---|
639 | for(InEdgeIt e(*_g,v) ; e!=INVALID; ++e) { |
---|
640 | if ( (*_capacity)[e] <= (*_flow)[e] ) continue; |
---|
641 | Node w=_g->source(e); |
---|
642 | if ( level[w] == _node_num && w != _source ) { |
---|
643 | bfs_queue.push(w); |
---|
644 | Node z=level_list[l]; |
---|
645 | if ( z!=INVALID ) left.set(z,w); |
---|
646 | right.set(w,z); |
---|
647 | level_list[l]=w; |
---|
648 | level.set(w, l); |
---|
649 | } |
---|
650 | } |
---|
651 | |
---|
652 | for(OutEdgeIt e(*_g,v) ; e!=INVALID; ++e) { |
---|
653 | if ( 0 >= (*_flow)[e] ) continue; |
---|
654 | Node w=_g->target(e); |
---|
655 | if ( level[w] == _node_num && w != _source ) { |
---|
656 | bfs_queue.push(w); |
---|
657 | Node z=level_list[l]; |
---|
658 | if ( z!=INVALID ) left.set(z,w); |
---|
659 | right.set(w,z); |
---|
660 | level_list[l]=w; |
---|
661 | level.set(w, l); |
---|
662 | } |
---|
663 | } |
---|
664 | } //while |
---|
665 | } //if |
---|
666 | |
---|
667 | |
---|
668 | switch (flow_prop) { |
---|
669 | case NO_FLOW: |
---|
670 | for(EdgeIt e(*_g); e!=INVALID; ++e) _flow->set(e,0); |
---|
671 | case ZERO_FLOW: |
---|
672 | for(NodeIt v(*_g); v!=INVALID; ++v) excess.set(v,0); |
---|
673 | |
---|
674 | //Reverse_bfs from t, to find the starting level. |
---|
675 | level.set(_target,0); |
---|
676 | bfs_queue.push(_target); |
---|
677 | |
---|
678 | while ( !bfs_queue.empty() ) { |
---|
679 | |
---|
680 | Node v=bfs_queue.front(); |
---|
681 | bfs_queue.pop(); |
---|
682 | int l=level[v]+1; |
---|
683 | |
---|
684 | for(InEdgeIt e(*_g,v) ; e!=INVALID; ++e) { |
---|
685 | Node w=_g->source(e); |
---|
686 | if ( level[w] == _node_num && w != _source ) { |
---|
687 | bfs_queue.push(w); |
---|
688 | Node z=level_list[l]; |
---|
689 | if ( z!=INVALID ) left.set(z,w); |
---|
690 | right.set(w,z); |
---|
691 | level_list[l]=w; |
---|
692 | level.set(w, l); |
---|
693 | } |
---|
694 | } |
---|
695 | } |
---|
696 | |
---|
697 | //the starting flow |
---|
698 | for(OutEdgeIt e(*_g,_source) ; e!=INVALID; ++e) { |
---|
699 | Num c=(*_capacity)[e]; |
---|
700 | if ( c <= 0 ) continue; |
---|
701 | Node w=_g->target(e); |
---|
702 | if ( level[w] < _node_num ) { |
---|
703 | if ( excess[w] <= 0 && w!=_target ) { //putting into the stack |
---|
704 | next.set(w,first[level[w]]); |
---|
705 | first[level[w]]=w; |
---|
706 | } |
---|
707 | _flow->set(e, c); |
---|
708 | excess.set(w, excess[w]+c); |
---|
709 | } |
---|
710 | } |
---|
711 | break; |
---|
712 | |
---|
713 | case GEN_FLOW: |
---|
714 | for(NodeIt v(*_g); v!=INVALID; ++v) excess.set(v,0); |
---|
715 | { |
---|
716 | Num exc=0; |
---|
717 | for(InEdgeIt e(*_g,_target) ; e!=INVALID; ++e) exc+=(*_flow)[e]; |
---|
718 | for(OutEdgeIt e(*_g,_target) ; e!=INVALID; ++e) exc-=(*_flow)[e]; |
---|
719 | excess.set(_target,exc); |
---|
720 | } |
---|
721 | |
---|
722 | //the starting flow |
---|
723 | for(OutEdgeIt e(*_g,_source); e!=INVALID; ++e) { |
---|
724 | Num rem=(*_capacity)[e]-(*_flow)[e]; |
---|
725 | if ( rem <= 0 ) continue; |
---|
726 | Node w=_g->target(e); |
---|
727 | if ( level[w] < _node_num ) { |
---|
728 | if ( excess[w] <= 0 && w!=_target ) { //putting into the stack |
---|
729 | next.set(w,first[level[w]]); |
---|
730 | first[level[w]]=w; |
---|
731 | } |
---|
732 | _flow->set(e, (*_capacity)[e]); |
---|
733 | excess.set(w, excess[w]+rem); |
---|
734 | } |
---|
735 | } |
---|
736 | |
---|
737 | for(InEdgeIt e(*_g,_source); e!=INVALID; ++e) { |
---|
738 | if ( (*_flow)[e] <= 0 ) continue; |
---|
739 | Node w=_g->source(e); |
---|
740 | if ( level[w] < _node_num ) { |
---|
741 | if ( excess[w] <= 0 && w!=_target ) { |
---|
742 | next.set(w,first[level[w]]); |
---|
743 | first[level[w]]=w; |
---|
744 | } |
---|
745 | excess.set(w, excess[w]+(*_flow)[e]); |
---|
746 | _flow->set(e, 0); |
---|
747 | } |
---|
748 | } |
---|
749 | break; |
---|
750 | |
---|
751 | case PRE_FLOW: |
---|
752 | //the starting flow |
---|
753 | for(OutEdgeIt e(*_g,_source) ; e!=INVALID; ++e) { |
---|
754 | Num rem=(*_capacity)[e]-(*_flow)[e]; |
---|
755 | if ( rem <= 0 ) continue; |
---|
756 | Node w=_g->target(e); |
---|
757 | if ( level[w] < _node_num ) _flow->set(e, (*_capacity)[e]); |
---|
758 | } |
---|
759 | |
---|
760 | for(InEdgeIt e(*_g,_source) ; e!=INVALID; ++e) { |
---|
761 | if ( (*_flow)[e] <= 0 ) continue; |
---|
762 | Node w=_g->source(e); |
---|
763 | if ( level[w] < _node_num ) _flow->set(e, 0); |
---|
764 | } |
---|
765 | |
---|
766 | //computing the excess |
---|
767 | for(NodeIt w(*_g); w!=INVALID; ++w) { |
---|
768 | Num exc=0; |
---|
769 | for(InEdgeIt e(*_g,w); e!=INVALID; ++e) exc+=(*_flow)[e]; |
---|
770 | for(OutEdgeIt e(*_g,w); e!=INVALID; ++e) exc-=(*_flow)[e]; |
---|
771 | excess.set(w,exc); |
---|
772 | |
---|
773 | //putting the active nodes into the stack |
---|
774 | int lev=level[w]; |
---|
775 | if ( exc > 0 && lev < _node_num && Node(w) != _target ) { |
---|
776 | next.set(w,first[lev]); |
---|
777 | first[lev]=w; |
---|
778 | } |
---|
779 | } |
---|
780 | break; |
---|
781 | } //switch |
---|
782 | } //preflowPreproc |
---|
783 | |
---|
784 | |
---|
785 | void relabel(Node w, int newlevel, VecNode& first, NNMap& next, |
---|
786 | VecNode& level_list, NNMap& left, |
---|
787 | NNMap& right, int& b, int& k, bool what_heur ) |
---|
788 | { |
---|
789 | |
---|
790 | int lev=level[w]; |
---|
791 | |
---|
792 | Node right_n=right[w]; |
---|
793 | Node left_n=left[w]; |
---|
794 | |
---|
795 | //unlacing starts |
---|
796 | if ( right_n!=INVALID ) { |
---|
797 | if ( left_n!=INVALID ) { |
---|
798 | right.set(left_n, right_n); |
---|
799 | left.set(right_n, left_n); |
---|
800 | } else { |
---|
801 | level_list[lev]=right_n; |
---|
802 | left.set(right_n, INVALID); |
---|
803 | } |
---|
804 | } else { |
---|
805 | if ( left_n!=INVALID ) { |
---|
806 | right.set(left_n, INVALID); |
---|
807 | } else { |
---|
808 | level_list[lev]=INVALID; |
---|
809 | } |
---|
810 | } |
---|
811 | //unlacing ends |
---|
812 | |
---|
813 | if ( level_list[lev]==INVALID ) { |
---|
814 | |
---|
815 | //gapping starts |
---|
816 | for (int i=lev; i!=k ; ) { |
---|
817 | Node v=level_list[++i]; |
---|
818 | while ( v!=INVALID ) { |
---|
819 | level.set(v,_node_num); |
---|
820 | v=right[v]; |
---|
821 | } |
---|
822 | level_list[i]=INVALID; |
---|
823 | if ( !what_heur ) first[i]=INVALID; |
---|
824 | } |
---|
825 | |
---|
826 | level.set(w,_node_num); |
---|
827 | b=lev-1; |
---|
828 | k=b; |
---|
829 | //gapping ends |
---|
830 | |
---|
831 | } else { |
---|
832 | |
---|
833 | if ( newlevel == _node_num ) level.set(w,_node_num); |
---|
834 | else { |
---|
835 | level.set(w,++newlevel); |
---|
836 | next.set(w,first[newlevel]); |
---|
837 | first[newlevel]=w; |
---|
838 | if ( what_heur ) b=newlevel; |
---|
839 | if ( k < newlevel ) ++k; //now k=newlevel |
---|
840 | Node z=level_list[newlevel]; |
---|
841 | if ( z!=INVALID ) left.set(z,w); |
---|
842 | right.set(w,z); |
---|
843 | left.set(w,INVALID); |
---|
844 | level_list[newlevel]=w; |
---|
845 | } |
---|
846 | } |
---|
847 | } //relabel |
---|
848 | |
---|
849 | }; |
---|
850 | |
---|
851 | ///Function type interface for Preflow algorithm. |
---|
852 | |
---|
853 | /// \ingroup flowalgs |
---|
854 | ///Function type interface for Preflow algorithm. |
---|
855 | ///\sa Preflow |
---|
856 | template<class GR, class CM, class FM> |
---|
857 | Preflow<GR,typename CM::Value,CM,FM> preflow(const GR &g, |
---|
858 | typename GR::Node source, |
---|
859 | typename GR::Node target, |
---|
860 | const CM &cap, |
---|
861 | FM &flow |
---|
862 | ) |
---|
863 | { |
---|
864 | return Preflow<GR,typename CM::Value,CM,FM>(g,source,target,cap,flow); |
---|
865 | } |
---|
866 | |
---|
867 | } //namespace lemon |
---|
868 | |
---|
869 | #endif //LEMON_PREFLOW_H |
---|