1 | // -*- c++ -*- |
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2 | #ifndef LEMON_MINLENGTHPATHS_H |
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3 | #define LEMON_MINLENGTHPATHS_H |
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4 | |
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5 | ///\ingroup galgs |
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6 | ///\file |
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7 | ///\brief An algorithm for finding k paths of minimal total length. |
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8 | |
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9 | #include <iostream> |
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10 | #include <lemon/dijkstra.h> |
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11 | #include <lemon/graph_wrapper.h> |
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12 | #include <lemon/maps.h> |
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13 | #include <vector> |
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14 | |
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15 | |
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16 | namespace lemon { |
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17 | |
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18 | /// \addtogroup galgs |
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19 | /// @{ |
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20 | |
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21 | ///\brief Implementation of an algorithm for finding k paths between 2 nodes |
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22 | /// of minimal total length |
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23 | /// |
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24 | /// The class \ref lemon::MinLengthPaths "MinLengthPaths" implements |
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25 | /// an algorithm for finding k edge-disjoint paths |
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26 | /// from a given source node to a given target node in an |
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27 | /// edge-weighted directed graph having minimal total weigth (length). |
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28 | /// |
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29 | ///\author Attila Bernath |
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30 | template <typename Graph, typename LengthMap> |
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31 | class MinLengthPaths { |
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32 | |
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33 | typedef typename LengthMap::ValueType Length; |
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34 | |
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35 | typedef typename Graph::Node Node; |
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36 | typedef typename Graph::NodeIt NodeIt; |
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37 | typedef typename Graph::Edge Edge; |
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38 | typedef typename Graph::OutEdgeIt OutEdgeIt; |
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39 | typedef typename Graph::template EdgeMap<int> EdgeIntMap; |
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40 | |
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41 | typedef ConstMap<Edge,int> ConstMap; |
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42 | |
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43 | typedef ResGraphWrapper<const Graph,int,ConstMap,EdgeIntMap> ResGraphType; |
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44 | |
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45 | class ModLengthMap { |
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46 | typedef typename ResGraphType::template NodeMap<Length> NodeMap; |
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47 | const ResGraphType& G; |
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48 | const EdgeIntMap& rev; |
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49 | const LengthMap &ol; |
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50 | const NodeMap &pot; |
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51 | public : |
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52 | typedef typename LengthMap::KeyType KeyType; |
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53 | typedef typename LengthMap::ValueType ValueType; |
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54 | |
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55 | ValueType operator[](typename ResGraphType::Edge e) const { |
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56 | //if ( (1-2*rev[e])*ol[e]-(pot[G.target(e)]-pot[G.source(e)] ) <0 ){ |
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57 | // std::cout<<"Negative length!!"<<std::endl; |
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58 | //} |
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59 | return (1-2*rev[e])*ol[e]-(pot[G.target(e)]-pot[G.source(e)]); |
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60 | } |
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61 | |
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62 | ModLengthMap(const ResGraphType& _G, const EdgeIntMap& _rev, |
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63 | const LengthMap &o, const NodeMap &p) : |
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64 | G(_G), rev(_rev), ol(o), pot(p){}; |
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65 | };//ModLengthMap |
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66 | |
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67 | |
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68 | |
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69 | |
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70 | const Graph& G; |
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71 | const LengthMap& length; |
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72 | |
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73 | //auxiliary variables |
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74 | |
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75 | //The value is 1 iff the edge is reversed. |
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76 | //If the algorithm has finished, the edges of the seeked paths are |
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77 | //exactly those that are reversed |
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78 | EdgeIntMap reversed; |
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79 | |
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80 | //Container to store found paths |
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81 | std::vector< std::vector<Edge> > paths; |
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82 | //typedef DirPath<Graph> DPath; |
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83 | //DPath paths; |
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84 | |
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85 | |
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86 | Length total_length; |
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87 | |
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88 | public : |
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89 | |
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90 | |
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91 | MinLengthPaths(Graph& _G, LengthMap& _length) : G(_G), |
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92 | length(_length), reversed(_G)/*, dijkstra_dist(_G)*/{ } |
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93 | |
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94 | |
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95 | ///Runs the algorithm. |
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96 | |
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97 | ///Runs the algorithm. |
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98 | ///Returns k if there are at least k edge-disjoint paths from s to t. |
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99 | ///Otherwise it returns the number of found edge-disjoint paths from s to t. |
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100 | int run(Node s, Node t, int k) { |
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101 | ConstMap const1map(1); |
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102 | |
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103 | |
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104 | //We need a residual graph, in which some of the edges are reversed |
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105 | ResGraphType res_graph(G, const1map, reversed); |
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106 | |
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107 | //Initialize the copy of the Dijkstra potential to zero |
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108 | typename ResGraphType::template NodeMap<Length> dijkstra_dist(res_graph); |
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109 | ModLengthMap mod_length(res_graph, reversed, length, dijkstra_dist); |
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110 | |
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111 | Dijkstra<ResGraphType, ModLengthMap> dijkstra(res_graph, mod_length); |
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112 | |
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113 | int i; |
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114 | for (i=0; i<k; ++i){ |
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115 | dijkstra.run(s); |
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116 | if (!dijkstra.reached(t)){ |
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117 | //There are no k paths from s to t |
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118 | break; |
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119 | }; |
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120 | |
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121 | { |
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122 | //We have to copy the potential |
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123 | typename ResGraphType::NodeIt n; |
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124 | for ( res_graph.first(n) ; res_graph.valid(n) ; res_graph.next(n) ) { |
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125 | dijkstra_dist[n] += dijkstra.distMap()[n]; |
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126 | } |
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127 | } |
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128 | |
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129 | |
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130 | //Reversing the sortest path |
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131 | Node n=t; |
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132 | Edge e; |
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133 | while (n!=s){ |
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134 | e = dijkstra.pred(n); |
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135 | n = dijkstra.predNode(n); |
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136 | reversed[e] = 1-reversed[e]; |
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137 | } |
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138 | |
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139 | |
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140 | } |
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141 | |
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142 | //Let's find the paths |
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143 | //We put the paths into stl vectors (as an inner representation). |
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144 | //In the meantime we lose the information stored in 'reversed'. |
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145 | //We suppose the lengths to be positive now. |
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146 | |
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147 | //Meanwhile we put the total length of the found paths |
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148 | //in the member variable total_length |
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149 | paths.clear(); |
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150 | total_length=0; |
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151 | paths.resize(k); |
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152 | for (int j=0; j<i; ++j){ |
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153 | Node n=s; |
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154 | OutEdgeIt e; |
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155 | |
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156 | while (n!=t){ |
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157 | |
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158 | |
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159 | G.first(e,n); |
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160 | |
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161 | while (!reversed[e]){ |
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162 | G.next(e); |
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163 | } |
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164 | n = G.target(e); |
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165 | paths[j].push_back(e); |
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166 | total_length += length[e]; |
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167 | reversed[e] = 1-reversed[e]; |
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168 | } |
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169 | |
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170 | } |
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171 | |
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172 | return i; |
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173 | } |
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174 | |
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175 | ///This function gives back the total length of the found paths. |
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176 | ///Assumes that \c run() has been run and nothing changed since then. |
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177 | Length totalLength(){ |
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178 | return total_length; |
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179 | } |
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180 | |
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181 | ///This function gives back the \c j-th path in argument p. |
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182 | ///Assumes that \c run() has been run and nothing changed since then. |
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183 | /// \warning It is assumed that \c p is constructed to be a path of graph \c G. If \c j is greater than the result of previous \c run, then the result here will be an empty path. |
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184 | template<typename DirPath> |
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185 | void getPath(DirPath& p, int j){ |
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186 | p.clear(); |
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187 | typename DirPath::Builder B(p); |
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188 | for(typename std::vector<Edge>::iterator i=paths[j].begin(); |
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189 | i!=paths[j].end(); ++i ){ |
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190 | B.pushBack(*i); |
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191 | } |
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192 | |
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193 | B.commit(); |
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194 | } |
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195 | |
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196 | }; //class MinLengthPaths |
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197 | |
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198 | ///@} |
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199 | |
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200 | } //namespace lemon |
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201 | |
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202 | #endif //LEMON_MINLENGTHPATHS_H |
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