1 | // -*- C++ -*- |
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2 | #ifndef HUGO_DIJKSTRA_H |
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3 | #define HUGO_DIJKSTRA_H |
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4 | |
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5 | ///\file |
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6 | ///\brief Dijkstra algorithm. |
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7 | |
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8 | #include <bin_heap.h> |
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9 | #include <invalid.h> |
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10 | |
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11 | namespace hugo { |
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12 | |
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13 | ///%Dijkstra algorithm class. |
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14 | |
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15 | ///This class provides an efficient implementation of %Dijkstra algorithm. |
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16 | ///The edge lengths are passed to the algorithm using a |
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17 | ///\ref ReadMapSkeleton "readable map", |
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18 | ///so it is easy to change it to any kind of length. |
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19 | /// |
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20 | ///The type of the length is determined by the \c ValueType of the length map. |
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21 | /// |
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22 | ///It is also possible to change the underlying priority heap. |
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23 | /// |
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24 | ///\param Graph The graph type the algorithm runs on. |
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25 | ///\param LengthMap This read-only |
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26 | ///EdgeMap |
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27 | ///determines the |
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28 | ///lengths of the edges. It is read once for each edge, so the map |
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29 | ///may involve in relatively time consuming process to compute the edge |
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30 | ///length if it is necessary. The default map type is |
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31 | ///\ref GraphSkeleton::EdgeMap "Graph::EdgeMap<int>" |
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32 | ///\param Heap The heap type used by the %Dijkstra |
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33 | ///algorithm. The default |
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34 | ///is using \ref BinHeap "binary heap". |
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35 | |
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36 | #ifdef DOXYGEN |
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37 | template <typename Graph, |
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38 | typename LengthMap, |
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39 | typename Heap> |
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40 | #else |
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41 | template <typename Graph, |
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42 | typename LengthMap=typename Graph::EdgeMap<int>, |
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43 | template <class,class,class> class Heap = BinHeap > |
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44 | #endif |
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45 | class Dijkstra{ |
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46 | public: |
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47 | typedef typename Graph::Node Node; |
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48 | typedef typename Graph::NodeIt NodeIt; |
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49 | typedef typename Graph::Edge Edge; |
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50 | typedef typename Graph::OutEdgeIt OutEdgeIt; |
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51 | |
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52 | typedef typename LengthMap::ValueType ValueType; |
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53 | typedef typename Graph::NodeMap<Edge> PredMap; |
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54 | typedef typename Graph::NodeMap<Node> PredNodeMap; |
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55 | typedef typename Graph::NodeMap<ValueType> DistMap; |
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56 | |
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57 | private: |
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58 | const Graph& G; |
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59 | const LengthMap& length; |
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60 | PredMap predecessor; |
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61 | PredNodeMap pred_node; |
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62 | DistMap distance; |
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63 | |
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64 | public : |
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65 | |
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66 | Dijkstra(Graph& _G, LengthMap& _length) : |
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67 | G(_G), length(_length), predecessor(_G), pred_node(_G), distance(_G) { } |
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68 | |
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69 | void run(Node s); |
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70 | |
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71 | ///The distance of a node from the root. |
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72 | |
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73 | ///Returns the distance of a node from the root. |
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74 | ///\pre \ref run() must be called before using this function. |
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75 | ///\warning If node \c v in unreachable from the root the return value |
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76 | ///of this funcion is undefined. |
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77 | ValueType dist(Node v) const { return distance[v]; } |
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78 | |
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79 | ///Returns the previous edge of the shortest path tree. |
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80 | |
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81 | ///For a node \c v it returns the previous edge of the shortest path tree, |
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82 | ///i.e. it returns the last edge from a shortest path from the root to \c |
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83 | ///v. It is INVALID if \c v is unreachable from the root or if \c v=s. The |
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84 | ///shortest path tree used here is equal to the shortest path tree used in |
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85 | ///\ref predNode(Node v). \pre \ref run() must be called before using |
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86 | ///this function. |
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87 | Edge pred(Node v) const { return predecessor[v]; } |
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88 | |
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89 | ///Returns the previous node of the shortest path tree. |
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90 | |
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91 | ///For a node \c v it returns the previous node of the shortest path tree, |
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92 | ///i.e. it returns the last but one node from a shortest path from the |
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93 | ///root to \c /v. It is INVALID if \c v is unreachable from the root or if |
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94 | ///\c v=s. The shortest path tree used here is equal to the shortest path |
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95 | ///tree used in \ref pred(Node v). \pre \ref run() must be called before |
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96 | ///using this function. |
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97 | Node predNode(Node v) const { return pred_node[v]; } |
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98 | |
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99 | ///Returns a reference to the NodeMap of distances. |
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100 | |
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101 | ///Returns a reference to the NodeMap of distances. \pre \ref run() must |
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102 | ///be called before using this function. |
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103 | const DistMap &distMap() const { return distance;} |
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104 | |
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105 | ///Returns a reference to the shortest path tree map. |
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106 | |
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107 | ///Returns a reference to the NodeMap of the edges of the |
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108 | ///shortest path tree. |
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109 | ///\pre \ref run() must be called before using this function. |
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110 | const PredMap &predMap() const { return predecessor;} |
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111 | |
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112 | ///Returns a reference to the map of nodes of shortest paths. |
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113 | |
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114 | ///Returns a reference to the NodeMap of the last but one nodes of the |
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115 | ///shortest path tree. |
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116 | ///\pre \ref run() must be called before using this function. |
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117 | const PredNodeMap &predNodeMap() const { return pred_node;} |
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118 | |
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119 | ///Checks if a node is reachable from the root. |
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120 | |
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121 | ///Returns \c true if \c v is reachable from the root. |
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122 | ///\warning the root node is reported to be unreached! |
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123 | ///\todo Is this what we want? |
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124 | ///\pre \ref run() must be called before using this function. |
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125 | /// |
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126 | bool reached(Node v) { return G.valid(predecessor[v]); } |
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127 | |
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128 | }; |
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129 | |
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130 | |
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131 | // ********************************************************************** |
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132 | // IMPLEMENTATIONS |
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133 | // ********************************************************************** |
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134 | |
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135 | ///Runs %Dijkstra algorithm from node the root. |
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136 | |
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137 | ///This method runs the %Dijkstra algorithm from a root node \c s |
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138 | ///in order to |
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139 | ///compute the |
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140 | ///shortest path to each node. The algorithm computes |
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141 | ///- The shortest path tree. |
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142 | ///- The distance of each node from the root. |
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143 | template <typename Graph, typename LengthMap, |
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144 | template<class,class,class> class Heap > |
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145 | void Dijkstra<Graph,LengthMap,Heap>::run(Node s) { |
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146 | |
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147 | NodeIt u; |
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148 | for ( G.first(u) ; G.valid(u) ; G.next(u) ) { |
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149 | predecessor.set(u,INVALID); |
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150 | pred_node.set(u,INVALID); |
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151 | } |
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152 | |
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153 | typename Graph::NodeMap<int> heap_map(G,-1); |
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154 | |
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155 | Heap<Node,ValueType,typename Graph::NodeMap<int> > heap(heap_map); |
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156 | |
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157 | heap.push(s,0); |
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158 | |
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159 | while ( !heap.empty() ) { |
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160 | |
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161 | Node v=heap.top(); |
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162 | ValueType oldvalue=heap[v]; |
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163 | heap.pop(); |
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164 | distance.set(v, oldvalue); |
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165 | |
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166 | { //FIXME this bracket is for e to be local |
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167 | OutEdgeIt e; |
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168 | for(G.first(e, v); |
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169 | G.valid(e); G.next(e)) { |
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170 | Node w=G.head(e); |
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171 | |
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172 | switch(heap.state(w)) { |
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173 | case heap.PRE_HEAP: |
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174 | heap.push(w,oldvalue+length[e]); |
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175 | predecessor.set(w,e); |
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176 | pred_node.set(w,v); |
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177 | break; |
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178 | case heap.IN_HEAP: |
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179 | if ( oldvalue+length[e] < heap[w] ) { |
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180 | heap.decrease(w, oldvalue+length[e]); |
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181 | predecessor.set(w,e); |
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182 | pred_node.set(w,v); |
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183 | } |
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184 | break; |
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185 | case heap.POST_HEAP: |
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186 | break; |
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187 | } |
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188 | } |
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189 | } //FIXME tis bracket |
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190 | } |
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191 | } |
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192 | |
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193 | } //END OF NAMESPACE HUGO |
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194 | |
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195 | #endif |
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196 | |
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197 | |
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