1 | /* -*- C++ -*- |
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2 | * src/lemon/path.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 | /** |
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18 | @defgroup paths Path Structures |
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19 | @ingroup datas |
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20 | \brief Path structures implemented in LEMON. |
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21 | |
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22 | LEMON provides flexible data structures |
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23 | to work with paths. |
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24 | |
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25 | All of them have the same interface, especially they can be built or extended |
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26 | using a standard Builder subclass. This make is easy to have e.g. the Dijkstra |
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27 | algorithm to store its result in any kind of path structure. |
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28 | |
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29 | \sa lemon::skeleton::Path |
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30 | |
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31 | */ |
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32 | |
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33 | ///\ingroup paths |
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34 | ///\file |
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35 | ///\brief Classes for representing paths in graphs. |
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36 | |
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37 | #ifndef LEMON_PATH_H |
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38 | #define LEMON_PATH_H |
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39 | |
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40 | #include <deque> |
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41 | #include <vector> |
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42 | #include <algorithm> |
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43 | |
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44 | #include <lemon/invalid.h> |
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45 | |
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46 | namespace lemon { |
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47 | |
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48 | /// \addtogroup paths |
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49 | /// @{ |
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50 | |
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51 | |
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52 | //! \brief A structure for representing directed paths in a graph. |
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53 | //! |
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54 | //! A structure for representing directed path in a graph. |
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55 | //! \param Graph The graph type in which the path is. |
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56 | //! \param DM DebugMode, defaults to DefaultDebugMode. |
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57 | //! |
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58 | //! In a sense, the path can be treated as a graph, for is has \c NodeIt |
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59 | //! and \c EdgeIt with the same usage. These types converts to the \c Node |
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60 | //! and \c Edge of the original graph. |
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61 | //! |
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62 | //! \todo Thoroughfully check all the range and consistency tests. |
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63 | template<typename Graph> |
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64 | class DirPath { |
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65 | public: |
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66 | /// Edge type of the underlying graph. |
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67 | typedef typename Graph::Edge GraphEdge; |
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68 | /// Node type of the underlying graph. |
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69 | typedef typename Graph::Node GraphNode; |
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70 | class NodeIt; |
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71 | class EdgeIt; |
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72 | |
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73 | protected: |
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74 | const Graph *gr; |
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75 | typedef std::vector<GraphEdge> Container; |
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76 | Container edges; |
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77 | |
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78 | public: |
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79 | |
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80 | /// \param _G The graph in which the path is. |
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81 | /// |
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82 | DirPath(const Graph &_G) : gr(&_G) {} |
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83 | |
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84 | /// \brief Subpath constructor. |
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85 | /// |
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86 | /// Subpath defined by two nodes. |
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87 | /// \warning It is an error if the two edges are not in order! |
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88 | DirPath(const DirPath &P, const NodeIt &a, const NodeIt &b) { |
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89 | gr = P.gr; |
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90 | edges.insert(edges.end(), P.edges.begin()+a.idx, P.edges.begin()+b.idx); |
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91 | } |
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92 | |
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93 | /// \brief Subpath constructor. |
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94 | /// |
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95 | /// Subpath defined by two edges. Contains edges in [a,b) |
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96 | /// \warning It is an error if the two edges are not in order! |
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97 | DirPath(const DirPath &P, const EdgeIt &a, const EdgeIt &b) { |
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98 | gr = P.gr; |
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99 | edges.insert(edges.end(), P.edges.begin()+a.idx, P.edges.begin()+b.idx); |
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100 | } |
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101 | |
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102 | /// Length of the path. |
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103 | size_t length() const { return edges.size(); } |
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104 | /// Returns whether the path is empty. |
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105 | bool empty() const { return edges.empty(); } |
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106 | |
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107 | /// Resets the path to an empty path. |
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108 | void clear() { edges.clear(); } |
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109 | |
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110 | /// \brief Starting point of the path. |
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111 | /// |
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112 | /// Starting point of the path. |
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113 | /// Returns INVALID if the path is empty. |
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114 | GraphNode tail() const { |
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115 | return empty() ? INVALID : gr->tail(edges[0]); |
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116 | } |
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117 | /// \brief End point of the path. |
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118 | /// |
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119 | /// End point of the path. |
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120 | /// Returns INVALID if the path is empty. |
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121 | GraphNode head() const { |
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122 | return empty() ? INVALID : gr->head(edges[length()-1]); |
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123 | } |
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124 | |
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125 | /// \brief Initializes node or edge iterator to point to the first |
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126 | /// node or edge. |
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127 | /// |
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128 | /// \sa nth |
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129 | template<typename It> |
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130 | It& first(It &i) const { return i=It(*this); } |
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131 | |
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132 | /// \brief Initializes node iterator to point to the node of a given index. |
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133 | NodeIt& nth(NodeIt &i, int n) const { |
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134 | return i=NodeIt(*this, n); |
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135 | } |
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136 | |
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137 | /// \brief Initializes edge iterator to point to the edge of a given index. |
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138 | EdgeIt& nth(EdgeIt &i, int n) const { |
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139 | return i=EdgeIt(*this, n); |
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140 | } |
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141 | |
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142 | /// \brief Returns node iterator pointing to the head node of the |
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143 | /// given edge iterator. |
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144 | NodeIt head(const EdgeIt& e) const { |
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145 | return NodeIt(*this, e.idx+1); |
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146 | } |
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147 | |
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148 | /// \brief Returns node iterator pointing to the tail node of the |
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149 | /// given edge iterator. |
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150 | NodeIt tail(const EdgeIt& e) const { |
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151 | return NodeIt(*this, e.idx); |
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152 | } |
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153 | |
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154 | |
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155 | /* Iterator classes */ |
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156 | |
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157 | /** |
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158 | * \brief Iterator class to iterate on the edges of the paths |
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159 | * |
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160 | * \ingroup paths |
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161 | * This class is used to iterate on the edges of the paths |
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162 | * |
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163 | * Of course it converts to Graph::Edge |
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164 | * |
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165 | */ |
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166 | class EdgeIt { |
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167 | friend class DirPath; |
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168 | |
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169 | int idx; |
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170 | const DirPath *p; |
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171 | public: |
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172 | /// Default constructor |
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173 | EdgeIt() {} |
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174 | /// Invalid constructor |
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175 | EdgeIt(Invalid) : idx(-1), p(0) {} |
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176 | /// Constructor with starting point |
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177 | EdgeIt(const DirPath &_p, int _idx = 0) : |
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178 | idx(_idx), p(&_p) { validate(); } |
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179 | |
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180 | ///Validity check |
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181 | bool valid() const { return idx!=-1; } |
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182 | |
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183 | ///Conversion to Graph::Edge |
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184 | operator GraphEdge () const { |
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185 | return valid() ? p->edges[idx] : INVALID; |
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186 | } |
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187 | |
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188 | /// Next edge |
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189 | EdgeIt& operator++() { ++idx; validate(); return *this; } |
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190 | |
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191 | /// Comparison operator |
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192 | bool operator==(const EdgeIt& e) const { return idx==e.idx; } |
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193 | /// Comparison operator |
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194 | bool operator!=(const EdgeIt& e) const { return idx!=e.idx; } |
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195 | /// Comparison operator |
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196 | bool operator<(const EdgeIt& e) const { return idx<e.idx; } |
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197 | |
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198 | private: |
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199 | // FIXME: comparison between signed and unsigned... |
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200 | // Jo ez igy? Vagy esetleg legyen a length() int? |
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201 | void validate() { if( size_t(idx) >= p->length() ) idx=-1; } |
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202 | }; |
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203 | |
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204 | /** |
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205 | * \brief Iterator class to iterate on the nodes of the paths |
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206 | * |
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207 | * \ingroup paths |
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208 | * This class is used to iterate on the nodes of the paths |
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209 | * |
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210 | * Of course it converts to Graph::Node |
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211 | * |
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212 | */ |
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213 | class NodeIt { |
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214 | friend class DirPath; |
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215 | |
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216 | int idx; |
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217 | const DirPath *p; |
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218 | public: |
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219 | /// Default constructor |
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220 | NodeIt() {} |
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221 | /// Invalid constructor |
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222 | NodeIt(Invalid) : idx(-1), p(0) {} |
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223 | /// Constructor with starting point |
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224 | NodeIt(const DirPath &_p, int _idx = 0) : |
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225 | idx(_idx), p(&_p) { validate(); } |
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226 | |
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227 | ///Validity check |
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228 | bool valid() const { return idx!=-1; } |
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229 | |
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230 | ///Conversion to Graph::Node |
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231 | operator const GraphNode& () const { |
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232 | if(idx >= p->length()) |
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233 | return p->head(); |
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234 | else if(idx >= 0) |
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235 | return p->gr->tail(p->edges[idx]); |
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236 | else |
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237 | return INVALID; |
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238 | } |
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239 | /// Next node |
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240 | NodeIt& operator++() { ++idx; validate(); return *this; } |
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241 | |
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242 | /// Comparison operator |
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243 | bool operator==(const NodeIt& e) const { return idx==e.idx; } |
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244 | /// Comparison operator |
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245 | bool operator!=(const NodeIt& e) const { return idx!=e.idx; } |
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246 | /// Comparison operator |
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247 | bool operator<(const NodeIt& e) const { return idx<e.idx; } |
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248 | |
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249 | private: |
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250 | void validate() { if( size_t(idx) > p->length() ) idx=-1; } |
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251 | }; |
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252 | |
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253 | friend class Builder; |
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254 | |
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255 | /** |
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256 | * \brief Class to build paths |
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257 | * |
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258 | * \ingroup paths |
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259 | * This class is used to fill a path with edges. |
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260 | * |
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261 | * You can push new edges to the front and to the back of the path in |
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262 | * arbitrary order then you should commit these changes to the graph. |
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263 | * |
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264 | * Fundamentally, for most "Paths" (classes fulfilling the |
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265 | * PathConcept) while the builder is active (after the first modifying |
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266 | * operation and until the commit()) the original Path is in a |
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267 | * "transitional" state (operations on it have undefined result). But |
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268 | * in the case of DirPath the original path remains unchanged until the |
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269 | * commit. However we don't recomend that you use this feature. |
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270 | */ |
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271 | class Builder { |
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272 | DirPath &P; |
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273 | Container front, back; |
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274 | |
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275 | public: |
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276 | ///\param _P the path you want to fill in. |
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277 | /// |
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278 | Builder(DirPath &_P) : P(_P) {} |
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279 | |
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280 | /// Sets the starting node of the path. |
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281 | |
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282 | /// Sets the starting node of the path. Edge added to the path |
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283 | /// afterwards have to be incident to this node. |
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284 | /// It should be called if and only if |
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285 | /// the path is empty and before any call to |
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286 | /// \ref pushFront() or \ref pushBack() |
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287 | void setStartNode(const GraphNode &) {} |
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288 | |
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289 | ///Push a new edge to the front of the path |
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290 | |
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291 | ///Push a new edge to the front of the path. |
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292 | ///\sa setStartNode |
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293 | void pushFront(const GraphEdge& e) { |
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294 | front.push_back(e); |
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295 | } |
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296 | |
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297 | ///Push a new edge to the back of the path |
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298 | |
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299 | ///Push a new edge to the back of the path. |
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300 | ///\sa setStartNode |
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301 | void pushBack(const GraphEdge& e) { |
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302 | back.push_back(e); |
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303 | } |
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304 | |
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305 | ///Commit the changes to the path. |
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306 | void commit() { |
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307 | if( !front.empty() || !back.empty() ) { |
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308 | Container tmp; |
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309 | tmp.reserve(front.size()+back.size()+P.length()); |
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310 | tmp.insert(tmp.end(), front.rbegin(), front.rend()); |
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311 | tmp.insert(tmp.end(), P.edges.begin(), P.edges.end()); |
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312 | tmp.insert(tmp.end(), back.begin(), back.end()); |
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313 | P.edges.swap(tmp); |
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314 | front.clear(); |
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315 | back.clear(); |
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316 | } |
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317 | } |
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318 | |
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319 | ///Reserve storage for the builder in advance. |
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320 | |
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321 | ///If you know a reasonable upper bound of the number of the edges |
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322 | ///to add to the front, using this function you can speed up the building. |
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323 | |
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324 | void reserveFront(size_t r) {front.reserve(r);} |
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325 | |
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326 | ///Reserve storage for the builder in advance. |
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327 | |
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328 | ///If you know a reasonable upper bound of the number of the edges |
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329 | ///to add to the back, using this function you can speed up the building. |
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330 | |
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331 | void reserveBack(size_t r) {back.reserve(r);} |
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332 | |
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333 | private: |
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334 | bool empty() { |
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335 | return front.empty() && back.empty() && P.empty(); |
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336 | } |
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337 | |
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338 | GraphNode tail() const { |
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339 | if( ! front.empty() ) |
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340 | return P.gr->tail(front[front.size()-1]); |
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341 | else if( ! P.empty() ) |
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342 | return P.gr->tail(P.edges[0]); |
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343 | else if( ! back.empty() ) |
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344 | return P.gr->tail(back[0]); |
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345 | else |
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346 | return INVALID; |
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347 | } |
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348 | GraphNode head() const { |
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349 | if( ! back.empty() ) |
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350 | return P.gr->head(back[back.size()-1]); |
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351 | else if( ! P.empty() ) |
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352 | return P.gr->head(P.edges[P.length()-1]); |
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353 | else if( ! front.empty() ) |
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354 | return P.gr->head(front[0]); |
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355 | else |
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356 | return INVALID; |
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357 | } |
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358 | |
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359 | }; |
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360 | |
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361 | }; |
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362 | |
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363 | |
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364 | |
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365 | |
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366 | |
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367 | |
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368 | |
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369 | |
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370 | |
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371 | |
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372 | /**********************************************************************/ |
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373 | |
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374 | |
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375 | //! \brief A structure for representing undirected path in a graph. |
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376 | //! |
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377 | //! A structure for representing undirected path in a graph. Ie. this is |
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378 | //! a path in a \e directed graph but the edges should not be directed |
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379 | //! forward. |
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380 | //! |
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381 | //! \param Graph The graph type in which the path is. |
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382 | //! \param DM DebugMode, defaults to DefaultDebugMode. |
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383 | //! |
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384 | //! In a sense, the path can be treated as a graph, for is has \c NodeIt |
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385 | //! and \c EdgeIt with the same usage. These types converts to the \c Node |
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386 | //! and \c Edge of the original graph. |
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387 | //! |
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388 | //! \todo Thoroughfully check all the range and consistency tests. |
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389 | template<typename Graph> |
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390 | class UndirPath { |
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391 | public: |
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392 | /// Edge type of the underlying graph. |
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393 | typedef typename Graph::Edge GraphEdge; |
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394 | /// Node type of the underlying graph. |
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395 | typedef typename Graph::Node GraphNode; |
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396 | class NodeIt; |
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397 | class EdgeIt; |
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398 | |
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399 | protected: |
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400 | const Graph *gr; |
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401 | typedef std::vector<GraphEdge> Container; |
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402 | Container edges; |
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403 | |
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404 | public: |
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405 | |
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406 | /// \param _G The graph in which the path is. |
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407 | /// |
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408 | UndirPath(const Graph &_G) : gr(&_G) {} |
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409 | |
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410 | /// \brief Subpath constructor. |
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411 | /// |
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412 | /// Subpath defined by two nodes. |
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413 | /// \warning It is an error if the two edges are not in order! |
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414 | UndirPath(const UndirPath &P, const NodeIt &a, const NodeIt &b) { |
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415 | gr = P.gr; |
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416 | edges.insert(edges.end(), P.edges.begin()+a.idx, P.edges.begin()+b.idx); |
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417 | } |
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418 | |
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419 | /// \brief Subpath constructor. |
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420 | /// |
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421 | /// Subpath defined by two edges. Contains edges in [a,b) |
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422 | /// \warning It is an error if the two edges are not in order! |
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423 | UndirPath(const UndirPath &P, const EdgeIt &a, const EdgeIt &b) { |
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424 | gr = P.gr; |
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425 | edges.insert(edges.end(), P.edges.begin()+a.idx, P.edges.begin()+b.idx); |
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426 | } |
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427 | |
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428 | /// Length of the path. |
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429 | size_t length() const { return edges.size(); } |
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430 | /// Returns whether the path is empty. |
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431 | bool empty() const { return edges.empty(); } |
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432 | |
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433 | /// Resets the path to an empty path. |
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434 | void clear() { edges.clear(); } |
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435 | |
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436 | /// \brief Starting point of the path. |
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437 | /// |
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438 | /// Starting point of the path. |
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439 | /// Returns INVALID if the path is empty. |
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440 | GraphNode tail() const { |
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441 | return empty() ? INVALID : gr->tail(edges[0]); |
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442 | } |
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443 | /// \brief End point of the path. |
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444 | /// |
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445 | /// End point of the path. |
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446 | /// Returns INVALID if the path is empty. |
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447 | GraphNode head() const { |
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448 | return empty() ? INVALID : gr->head(edges[length()-1]); |
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449 | } |
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450 | |
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451 | /// \brief Initializes node or edge iterator to point to the first |
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452 | /// node or edge. |
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453 | /// |
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454 | /// \sa nth |
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455 | template<typename It> |
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456 | It& first(It &i) const { return i=It(*this); } |
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457 | |
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458 | /// \brief Initializes node iterator to point to the node of a given index. |
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459 | NodeIt& nth(NodeIt &i, int n) const { |
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460 | return i=NodeIt(*this, n); |
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461 | } |
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462 | |
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463 | /// \brief Initializes edge iterator to point to the edge of a given index. |
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464 | EdgeIt& nth(EdgeIt &i, int n) const { |
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465 | return i=EdgeIt(*this, n); |
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466 | } |
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467 | |
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468 | /// Checks validity of a node or edge iterator. |
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469 | template<typename It> |
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470 | static |
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471 | bool valid(const It &i) { return i.valid(); } |
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472 | |
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473 | /// Steps the given node or edge iterator. |
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474 | template<typename It> |
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475 | static |
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476 | It& next(It &e) { |
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477 | return ++e; |
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478 | } |
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479 | |
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480 | /// \brief Returns node iterator pointing to the head node of the |
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481 | /// given edge iterator. |
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482 | NodeIt head(const EdgeIt& e) const { |
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483 | return NodeIt(*this, e.idx+1); |
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484 | } |
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485 | |
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486 | /// \brief Returns node iterator pointing to the tail node of the |
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487 | /// given edge iterator. |
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488 | NodeIt tail(const EdgeIt& e) const { |
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489 | return NodeIt(*this, e.idx); |
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490 | } |
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491 | |
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492 | |
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493 | |
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494 | /** |
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495 | * \brief Iterator class to iterate on the edges of the paths |
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496 | * |
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497 | * \ingroup paths |
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498 | * This class is used to iterate on the edges of the paths |
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499 | * |
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500 | * Of course it converts to Graph::Edge |
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501 | * |
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502 | * \todo Its interface differs from the standard edge iterator. |
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503 | * Yes, it shouldn't. |
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504 | */ |
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505 | class EdgeIt { |
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506 | friend class UndirPath; |
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507 | |
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508 | int idx; |
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509 | const UndirPath *p; |
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510 | public: |
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511 | /// Default constructor |
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512 | EdgeIt() {} |
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513 | /// Invalid constructor |
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514 | EdgeIt(Invalid) : idx(-1), p(0) {} |
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515 | /// Constructor with starting point |
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516 | EdgeIt(const UndirPath &_p, int _idx = 0) : |
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517 | idx(_idx), p(&_p) { validate(); } |
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518 | |
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519 | ///Validity check |
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520 | bool valid() const { return idx!=-1; } |
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521 | |
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522 | ///Conversion to Graph::Edge |
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523 | operator GraphEdge () const { |
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524 | return valid() ? p->edges[idx] : INVALID; |
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525 | } |
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526 | /// Next edge |
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527 | EdgeIt& operator++() { ++idx; validate(); return *this; } |
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528 | |
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529 | /// Comparison operator |
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530 | bool operator==(const EdgeIt& e) const { return idx==e.idx; } |
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531 | /// Comparison operator |
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532 | bool operator!=(const EdgeIt& e) const { return idx!=e.idx; } |
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533 | /// Comparison operator |
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534 | bool operator<(const EdgeIt& e) const { return idx<e.idx; } |
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535 | |
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536 | private: |
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537 | // FIXME: comparison between signed and unsigned... |
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538 | // Jo ez igy? Vagy esetleg legyen a length() int? |
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539 | void validate() { if( size_t(idx) >= p->length() ) idx=-1; } |
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540 | }; |
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541 | |
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542 | /** |
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543 | * \brief Iterator class to iterate on the nodes of the paths |
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544 | * |
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545 | * \ingroup paths |
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546 | * This class is used to iterate on the nodes of the paths |
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547 | * |
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548 | * Of course it converts to Graph::Node |
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549 | * |
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550 | * \todo Its interface differs from the standard node iterator. |
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551 | * Yes, it shouldn't. |
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552 | */ |
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553 | class NodeIt { |
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554 | friend class UndirPath; |
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555 | |
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556 | int idx; |
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557 | const UndirPath *p; |
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558 | public: |
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559 | /// Default constructor |
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560 | NodeIt() {} |
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561 | /// Invalid constructor |
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562 | NodeIt(Invalid) : idx(-1), p(0) {} |
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563 | /// Constructor with starting point |
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564 | NodeIt(const UndirPath &_p, int _idx = 0) : |
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565 | idx(_idx), p(&_p) { validate(); } |
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566 | |
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567 | ///Validity check |
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568 | bool valid() const { return idx!=-1; } |
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569 | |
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570 | ///Conversion to Graph::Node |
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571 | operator const GraphNode& () const { |
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572 | if(idx >= p->length()) |
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573 | return p->head(); |
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574 | else if(idx >= 0) |
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575 | return p->gr->tail(p->edges[idx]); |
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576 | else |
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577 | return INVALID; |
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578 | } |
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579 | /// Next node |
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580 | NodeIt& operator++() { ++idx; validate(); return *this; } |
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581 | |
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582 | /// Comparison operator |
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583 | bool operator==(const NodeIt& e) const { return idx==e.idx; } |
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584 | /// Comparison operator |
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585 | bool operator!=(const NodeIt& e) const { return idx!=e.idx; } |
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586 | /// Comparison operator |
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587 | bool operator<(const NodeIt& e) const { return idx<e.idx; } |
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588 | |
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589 | private: |
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590 | void validate() { if( size_t(idx) > p->length() ) idx=-1; } |
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591 | }; |
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592 | |
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593 | friend class Builder; |
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594 | |
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595 | /** |
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596 | * \brief Class to build paths |
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597 | * |
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598 | * \ingroup paths |
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599 | * This class is used to fill a path with edges. |
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600 | * |
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601 | * You can push new edges to the front and to the back of the path in |
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602 | * arbitrary order then you should commit these changes to the graph. |
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603 | * |
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604 | * Fundamentally, for most "Paths" (classes fulfilling the |
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605 | * PathConcept) while the builder is active (after the first modifying |
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606 | * operation and until the commit()) the original Path is in a |
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607 | * "transitional" state (operations ot it have undefined result). But |
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608 | * in the case of UndirPath the original path is unchanged until the |
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609 | * commit. However we don't recomend that you use this feature. |
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610 | */ |
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611 | class Builder { |
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612 | UndirPath &P; |
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613 | Container front, back; |
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614 | |
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615 | public: |
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616 | ///\param _P the path you want to fill in. |
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617 | /// |
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618 | Builder(UndirPath &_P) : P(_P) {} |
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619 | |
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620 | /// Sets the starting node of the path. |
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621 | |
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622 | /// Sets the starting node of the path. Edge added to the path |
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623 | /// afterwards have to be incident to this node. |
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624 | /// It should be called if and only if |
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625 | /// the path is empty and before any call to |
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626 | /// \ref pushFront() or \ref pushBack() |
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627 | void setStartNode(const GraphNode &) {} |
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628 | |
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629 | ///Push a new edge to the front of the path |
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630 | |
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631 | ///Push a new edge to the front of the path. |
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632 | ///\sa setStartNode |
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633 | void pushFront(const GraphEdge& e) { |
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634 | front.push_back(e); |
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635 | } |
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636 | |
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637 | ///Push a new edge to the back of the path |
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638 | |
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639 | ///Push a new edge to the back of the path. |
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640 | ///\sa setStartNode |
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641 | void pushBack(const GraphEdge& e) { |
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642 | back.push_back(e); |
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643 | } |
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644 | |
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645 | ///Commit the changes to the path. |
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646 | void commit() { |
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647 | if( !(front.empty() && back.empty()) ) { |
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648 | Container tmp; |
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649 | tmp.reserve(front.size()+back.size()+P.length()); |
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650 | tmp.insert(tmp.end(), front.rbegin(), front.rend()); |
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651 | tmp.insert(tmp.end(), P.edges.begin(), P.edges.end()); |
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652 | tmp.insert(tmp.end(), back.begin(), back.end()); |
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653 | P.edges.swap(tmp); |
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654 | front.clear(); |
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655 | back.clear(); |
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656 | } |
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657 | } |
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658 | |
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659 | |
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660 | ///Reserve storage for the builder in advance. |
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661 | |
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662 | ///If you know a reasonable upper bound of the number of the edges |
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663 | ///to add to the front, using this function you can speed up the building. |
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664 | |
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665 | void reserveFront(size_t r) {front.reserve(r);} |
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666 | |
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667 | ///Reserve storage for the builder in advance. |
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668 | |
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669 | ///If you know a reasonable upper bound of the number of the edges |
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670 | ///to add to the back, using this function you can speed up the building. |
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671 | |
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672 | void reserveBack(size_t r) {back.reserve(r);} |
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673 | |
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674 | private: |
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675 | bool empty() { |
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676 | return front.empty() && back.empty() && P.empty(); |
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677 | } |
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678 | |
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679 | GraphNode tail() const { |
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680 | if( ! front.empty() ) |
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681 | return P.gr->tail(front[front.size()-1]); |
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682 | else if( ! P.empty() ) |
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683 | return P.gr->tail(P.edges[0]); |
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684 | else if( ! back.empty() ) |
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685 | return P.gr->tail(back[0]); |
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686 | else |
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687 | return INVALID; |
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688 | } |
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689 | GraphNode head() const { |
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690 | if( ! back.empty() ) |
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691 | return P.gr->head(back[back.size()-1]); |
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692 | else if( ! P.empty() ) |
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693 | return P.gr->head(P.edges[P.length()-1]); |
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694 | else if( ! front.empty() ) |
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695 | return P.gr->head(front[0]); |
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696 | else |
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697 | return INVALID; |
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698 | } |
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699 | |
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700 | }; |
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701 | |
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702 | }; |
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703 | |
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704 | |
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705 | ///@} |
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706 | |
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707 | } // namespace lemon |
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708 | |
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709 | #endif // LEMON_PATH_H |
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