1 | /* -*- C++ -*- |
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2 | * src/lemon/bfs.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_BFS_H |
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18 | #define LEMON_BFS_H |
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19 | |
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20 | ///\ingroup flowalgs |
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21 | ///\file |
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22 | ///\brief Bfs algorithm. |
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23 | /// |
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24 | ///\todo Revise Manual. |
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25 | |
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26 | #include <lemon/bin_heap.h> |
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27 | #include <lemon/invalid.h> |
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28 | |
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29 | namespace lemon { |
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30 | |
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31 | /// \addtogroup flowalgs |
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32 | /// @{ |
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33 | |
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34 | ///%BFS algorithm class. |
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35 | |
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36 | ///This class provides an efficient implementation of %BFS algorithm. |
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37 | ///\param GR The graph type the algorithm runs on. |
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38 | ///This class does the same as Dijkstra does with constant 1 edge length, |
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39 | ///but it is faster. |
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40 | /// |
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41 | ///\author Alpar Juttner |
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42 | |
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43 | #ifdef DOXYGEN |
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44 | template <typename GR> |
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45 | #else |
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46 | template <typename GR> |
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47 | #endif |
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48 | class Bfs{ |
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49 | public: |
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50 | ///The type of the underlying graph. |
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51 | typedef GR Graph; |
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52 | ///\e |
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53 | typedef typename Graph::Node Node; |
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54 | ///\e |
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55 | typedef typename Graph::NodeIt NodeIt; |
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56 | ///\e |
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57 | typedef typename Graph::Edge Edge; |
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58 | ///\e |
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59 | typedef typename Graph::OutEdgeIt OutEdgeIt; |
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60 | |
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61 | ///\brief The type of the map that stores the last |
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62 | ///edges of the shortest paths. |
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63 | typedef typename Graph::template NodeMap<Edge> PredMap; |
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64 | ///\brief The type of the map that stores the last but one |
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65 | ///nodes of the shortest paths. |
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66 | typedef typename Graph::template NodeMap<Node> PredNodeMap; |
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67 | ///The type of the map that stores the dists of the nodes. |
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68 | typedef typename Graph::template NodeMap<int> DistMap; |
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69 | |
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70 | private: |
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71 | /// Pointer to the underlying graph. |
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72 | const Graph *G; |
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73 | ///Pointer to the map of predecessors edges. |
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74 | PredMap *predecessor; |
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75 | ///Indicates if \ref predecessor is locally allocated (\c true) or not. |
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76 | bool local_predecessor; |
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77 | ///Pointer to the map of predecessors nodes. |
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78 | PredNodeMap *pred_node; |
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79 | ///Indicates if \ref pred_node is locally allocated (\c true) or not. |
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80 | bool local_pred_node; |
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81 | ///Pointer to the map of distances. |
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82 | DistMap *distance; |
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83 | ///Indicates if \ref distance is locally allocated (\c true) or not. |
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84 | bool local_distance; |
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85 | |
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86 | ///The source node of the last execution. |
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87 | Node source; |
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88 | |
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89 | |
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90 | ///Initializes the maps. |
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91 | void init_maps() |
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92 | { |
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93 | if(!predecessor) { |
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94 | local_predecessor = true; |
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95 | predecessor = new PredMap(*G); |
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96 | } |
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97 | if(!pred_node) { |
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98 | local_pred_node = true; |
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99 | pred_node = new PredNodeMap(*G); |
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100 | } |
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101 | if(!distance) { |
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102 | local_distance = true; |
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103 | distance = new DistMap(*G); |
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104 | } |
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105 | } |
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106 | |
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107 | public : |
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108 | ///Constructor. |
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109 | |
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110 | ///\param _G the graph the algorithm will run on. |
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111 | /// |
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112 | Bfs(const Graph& _G) : |
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113 | G(&_G), |
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114 | predecessor(NULL), local_predecessor(false), |
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115 | pred_node(NULL), local_pred_node(false), |
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116 | distance(NULL), local_distance(false) |
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117 | { } |
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118 | |
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119 | ///Destructor. |
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120 | ~Bfs() |
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121 | { |
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122 | if(local_predecessor) delete predecessor; |
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123 | if(local_pred_node) delete pred_node; |
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124 | if(local_distance) delete distance; |
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125 | } |
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126 | |
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127 | ///Sets the map storing the predecessor edges. |
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128 | |
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129 | ///Sets the map storing the predecessor edges. |
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130 | ///If you don't use this function before calling \ref run(), |
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131 | ///it will allocate one. The destuctor deallocates this |
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132 | ///automatically allocated map, of course. |
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133 | ///\return <tt> (*this) </tt> |
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134 | Bfs &setPredMap(PredMap &m) |
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135 | { |
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136 | if(local_predecessor) { |
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137 | delete predecessor; |
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138 | local_predecessor=false; |
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139 | } |
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140 | predecessor = &m; |
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141 | return *this; |
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142 | } |
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143 | |
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144 | ///Sets the map storing the predecessor nodes. |
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145 | |
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146 | ///Sets the map storing the predecessor nodes. |
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147 | ///If you don't use this function before calling \ref run(), |
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148 | ///it will allocate one. The destuctor deallocates this |
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149 | ///automatically allocated map, of course. |
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150 | ///\return <tt> (*this) </tt> |
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151 | Bfs &setPredNodeMap(PredNodeMap &m) |
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152 | { |
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153 | if(local_pred_node) { |
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154 | delete pred_node; |
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155 | local_pred_node=false; |
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156 | } |
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157 | pred_node = &m; |
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158 | return *this; |
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159 | } |
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160 | |
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161 | ///Sets the map storing the distances calculated by the algorithm. |
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162 | |
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163 | ///Sets the map storing the distances calculated by the algorithm. |
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164 | ///If you don't use this function before calling \ref run(), |
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165 | ///it will allocate one. The destuctor deallocates this |
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166 | ///automatically allocated map, of course. |
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167 | ///\return <tt> (*this) </tt> |
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168 | Bfs &setDistMap(DistMap &m) |
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169 | { |
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170 | if(local_distance) { |
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171 | delete distance; |
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172 | local_distance=false; |
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173 | } |
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174 | distance = &m; |
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175 | return *this; |
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176 | } |
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177 | |
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178 | ///Runs %BFS algorithm from node \c s. |
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179 | |
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180 | ///This method runs the %BFS algorithm from a root node \c s |
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181 | ///in order to |
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182 | ///compute a |
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183 | ///shortest path to each node. The algorithm computes |
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184 | ///- The %BFS tree. |
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185 | ///- The distance of each node from the root. |
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186 | |
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187 | void run(Node s) { |
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188 | |
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189 | init_maps(); |
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190 | |
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191 | source = s; |
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192 | |
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193 | for ( NodeIt u(*G) ; u!=INVALID ; ++u ) { |
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194 | predecessor->set(u,INVALID); |
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195 | pred_node->set(u,INVALID); |
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196 | } |
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197 | |
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198 | int N=G->nodeNum(); |
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199 | std::vector<typename Graph::Node> Q(N); |
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200 | int Qh=0; |
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201 | int Qt=0; |
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202 | |
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203 | Q[Qh++]=source; |
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204 | distance->set(s, 0); |
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205 | do { |
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206 | Node m; |
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207 | Node n=Q[Qt++]; |
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208 | int d= (*distance)[n]+1; |
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209 | |
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210 | for(OutEdgeIt e(*G,n);e!=INVALID;++e) |
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211 | if((m=G->head(e))!=s && (*predecessor)[m]==INVALID) { |
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212 | Q[Qh++]=m; |
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213 | predecessor->set(m,e); |
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214 | pred_node->set(m,n); |
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215 | distance->set(m,d); |
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216 | } |
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217 | } while(Qt!=Qh); |
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218 | } |
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219 | |
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220 | ///The distance of a node from the root. |
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221 | |
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222 | ///Returns the distance of a node from the root. |
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223 | ///\pre \ref run() must be called before using this function. |
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224 | ///\warning If node \c v in unreachable from the root the return value |
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225 | ///of this funcion is undefined. |
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226 | int dist(Node v) const { return (*distance)[v]; } |
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227 | |
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228 | ///Returns the 'previous edge' of the %BFS path tree. |
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229 | |
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230 | ///For a node \c v it returns the 'previous edge' of the %BFS tree, |
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231 | ///i.e. it returns the last edge of a shortest path from the root to \c |
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232 | ///v. It is \ref INVALID |
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233 | ///if \c v is unreachable from the root or if \c v=s. The |
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234 | ///%BFS tree used here is equal to the %BFS tree used in |
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235 | ///\ref predNode(Node v). \pre \ref run() must be called before using |
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236 | ///this function. |
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237 | Edge pred(Node v) const { return (*predecessor)[v]; } |
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238 | |
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239 | ///Returns the 'previous node' of the %BFS tree. |
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240 | |
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241 | ///For a node \c v it returns the 'previous node' on the %BFS tree, |
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242 | ///i.e. it returns the last but one node from a shortest path from the |
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243 | ///root to \c /v. It is INVALID if \c v is unreachable from the root or if |
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244 | ///\c v=s. The shortest path tree used here is equal to the %BFS |
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245 | ///tree used in \ref pred(Node v). \pre \ref run() must be called before |
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246 | ///using this function. |
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247 | Node predNode(Node v) const { return (*pred_node)[v]; } |
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248 | |
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249 | ///Returns a reference to the NodeMap of distances. |
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250 | |
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251 | ///Returns a reference to the NodeMap of distances. \pre \ref run() must |
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252 | ///be called before using this function. |
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253 | const DistMap &distMap() const { return *distance;} |
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254 | |
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255 | ///Returns a reference to the %BFS tree map. |
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256 | |
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257 | ///Returns a reference to the NodeMap of the edges of the |
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258 | ///%BFS tree. |
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259 | ///\pre \ref run() must be called before using this function. |
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260 | const PredMap &predMap() const { return *predecessor;} |
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261 | |
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262 | ///Returns a reference to the map of last but one nodes of shortest paths. |
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263 | |
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264 | ///Returns a reference to the NodeMap of the last but one nodes on the |
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265 | ///%BFS tree. |
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266 | ///\pre \ref run() must be called before using this function. |
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267 | const PredNodeMap &predNodeMap() const { return *pred_node;} |
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268 | |
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269 | ///Checks if a node is reachable from the root. |
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270 | |
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271 | ///Returns \c true if \c v is reachable from the root. |
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272 | ///\note The root node is reported to be reached! |
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273 | /// |
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274 | ///\pre \ref run() must be called before using this function. |
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275 | /// |
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276 | bool reached(Node v) { return v==source || (*predecessor)[v]!=INVALID; } |
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277 | |
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278 | }; |
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279 | |
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280 | /// @} |
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281 | |
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282 | } //END OF NAMESPACE LEMON |
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283 | |
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284 | #endif |
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285 | |
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286 | |
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