1 | /* -*- mode: C++; indent-tabs-mode: nil; -*- |
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2 | * |
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3 | * This file is a part of LEMON, a generic C++ optimization library. |
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4 | * |
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5 | * Copyright (C) 2003-2010 |
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6 | * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport |
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7 | * (Egervary Research Group on Combinatorial Optimization, EGRES). |
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8 | * |
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9 | * Permission to use, modify and distribute this software is granted |
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10 | * provided that this copyright notice appears in all copies. For |
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11 | * precise terms see the accompanying LICENSE file. |
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12 | * |
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13 | * This software is provided "AS IS" with no warranty of any kind, |
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14 | * express or implied, and with no claim as to its suitability for any |
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15 | * purpose. |
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16 | * |
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17 | */ |
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18 | |
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19 | namespace lemon { |
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20 | /** |
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21 | [PAGE]sec_graph_structures[PAGE] Graph Structures |
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22 | |
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23 | The implementation of combinatorial algorithms heavily relies on |
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24 | efficient graph structures. Diverse applications require the |
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25 | usage of different physical graph storages. |
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26 | In \ref sec_basics, we have introduced a general digraph structure, |
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27 | \ref ListDigraph. Apart from this class, LEMON provides several |
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28 | other classes for handling directed and undirected graphs to meet the |
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29 | diverging requirements of the possible users. In order to save on running |
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30 | time or on memory usage, some structures may fail to support some graph |
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31 | features like node or arc/edge deletion. |
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32 | You are free to use the graph structure that fit your requirements the best, |
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33 | since most graph algorithms and auxiliary data structures can be used |
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34 | with any of them. |
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35 | |
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36 | |
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37 | [SEC]sec_graph_concepts[SEC] Graph Concepts |
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38 | |
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39 | In LEMON, there are various graph types, which are rather different, but |
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40 | they all conform to the corresponding \ref graph_concepts "graph concept", |
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41 | which defines the common part of the graph interfaces. |
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42 | The \ref concepts::Digraph "Digraph concept" describes the common interface |
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43 | of directed graphs (without any sensible implementation), while |
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44 | the \ref concepts::Graph "Graph concept" describes the undirected graphs. |
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45 | A generic graph algorithm should only exploit the features of the |
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46 | corresponding graph concept so that it could be applied to any graph |
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47 | structure. (Such an algorithm should compile with the |
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48 | \ref concepts::Digraph "Digraph" or \ref concepts::Graph "Graph" type, |
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49 | but it will not run properly, of course.) |
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50 | |
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51 | The graph %concepts define the member classes for the iterators and maps |
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52 | along with some useful basic functions for obtaining the identifiers of |
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53 | the items, the end nodes of the arcs (or edges) and their iterators, |
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54 | etc. |
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55 | An actual graph implementation may have various additional functionalities |
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56 | according to its purpose. |
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57 | |
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58 | Another advantage of this design is that you can write your own graph classes, |
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59 | if you would like to. |
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60 | As long as they provide the interface defined in one of the graph concepts, |
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61 | all the LEMON algorithms and classes will work with them properly. |
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62 | |
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63 | |
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64 | [SEC]sec_digraph_types[SEC] Digraph Structures |
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65 | |
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66 | The already used \ref ListDigraph class is the most versatile directed |
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67 | graph structure. As its name suggests, it is based on linked lists, |
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68 | therefore iterating through its nodes and arcs is fast and it is quite |
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69 | flexible. Apart from the general digraph functionalities, it |
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70 | provides operations for adding and removing nodes and arcs, changing |
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71 | the source or target node of an arc, and contracting and splitting nodes |
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72 | or arcs. |
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73 | |
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74 | \ref SmartDigraph is another general digraph implementation, which is |
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75 | significantly more efficient (both in terms of space and time), but it |
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76 | provides less functionality. For example, nodes and arcs cannot be |
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77 | removed from it. |
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78 | |
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79 | The \ref StaticDigraph structure is even more optimized for efficiency, |
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80 | but it is completely static. It requires less space in memory and |
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81 | provides faster item iteration than \ref ListDigraph and \ref |
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82 | SmartDigraph, especially using \ref concepts::Digraph::OutArcIt |
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83 | "OutArcIt" iterators, since its arcs are stored in an appropriate order. |
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84 | However, it only provides \ref StaticDigraph::build() "build()" and |
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85 | \ref \ref StaticDigraph::clear() "clear()" functions and does not |
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86 | support any other modification of the digraph. |
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87 | |
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88 | \ref FullDigraph is an efficient implementation of a directed full graph. |
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89 | This structure is also completely static, so you can neither add nor delete |
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90 | arcs or nodes, moreover, the class needs constant space in memory. |
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91 | |
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92 | |
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93 | [SEC]sec_undir_graphs[SEC] Undirected Graphs |
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94 | |
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95 | LEMON also provides undirected graph structures. For example, |
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96 | \ref ListGraph and \ref SmartGraph are the undirected versions of |
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97 | \ref ListDigraph and \ref SmartDigraph, respectively. |
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98 | They provide similar features to the digraph structures. |
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99 | |
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100 | The \ref concepts::Graph "undirected graphs" also fulfill the concept of |
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101 | \ref concepts::Digraph "directed graphs", in such a way that each |
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102 | undirected \e edge of a graph can also be regarded as two oppositely |
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103 | directed \e arcs. As a result, all directed graph algorithms automatically |
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104 | run on undirected graphs, as well. |
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105 | |
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106 | Undirected graphs provide an \c Edge type for the \e undirected \e edges |
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107 | and an \c Arc type for the \e directed \e arcs. The \c Arc type is |
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108 | convertible to \c Edge (or inherited from it), thus the corresponding |
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109 | edge can always be obtained from an arc. |
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110 | |
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111 | Only nodes and edges can be added to or removed from an undirected |
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112 | graph and the corresponding arcs are added or removed automatically |
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113 | (there are twice as many arcs as edges) |
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114 | |
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115 | For example, |
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116 | \code |
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117 | ListGraph g; |
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118 | |
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119 | ListGraph::Node a = g.addNode(); |
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120 | ListGraph::Node b = g.addNode(); |
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121 | ListGraph::Node c = g.addNode(); |
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122 | |
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123 | ListGraph::Edge e = g.addEdge(a,b); |
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124 | g.addEdge(b,c); |
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125 | g.addEdge(c,a); |
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126 | \endcode |
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127 | |
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128 | Each edge has an inherent orientation, thus it can be defined whether an |
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129 | arc is forward or backward oriented in an undirected graph with respect |
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130 | to this default oriantation of the represented edge. |
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131 | The direction of an arc can be obtained and set using the functions |
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132 | \ref concepts::Graph::direction() "direction()" and |
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133 | \ref concepts::Graph::direct() "direct()", respectively. |
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134 | |
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135 | For example, |
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136 | \code |
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137 | ListGraph::Arc a1 = g.direct(e, true); // a1 is the forward arc |
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138 | ListGraph::Arc a2 = g.direct(e, false); // a2 is the backward arc |
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139 | |
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140 | if (a2 == g.oppositeArc(a1)) |
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141 | std::cout << "a2 is the opposite of a1" << std::endl; |
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142 | \endcode |
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143 | |
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144 | The end nodes of an edge can be obtained using the functions |
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145 | \ref concepts::Graph::source() "u()" and |
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146 | \ref concepts::Graph::target() "v()", while the |
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147 | \ref concepts::Graph::source() "source()" and |
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148 | \ref concepts::Graph::target() "target()" can be used for arcs. |
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149 | |
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150 | \code |
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151 | std::cout << "Edge " << g.id(e) << " connects node " |
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152 | << g.id(g.u(e)) << " and node " << g.id(g.v(e)) << std::endl; |
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153 | |
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154 | std::cout << "Arc " << g.id(a2) << " goes from node " |
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155 | << g.id(g.source(a2)) << " to node " << g.id(g.target(a2)) << std::endl; |
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156 | \endcode |
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157 | |
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158 | |
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159 | Similarly to the digraphs, the undirected graphs also provide iterators |
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160 | \ref concepts::Graph::NodeIt "NodeIt", \ref concepts::Graph::ArcIt "ArcIt", |
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161 | \ref concepts::Graph::OutArcIt "OutArcIt" and \ref concepts::Graph::InArcIt |
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162 | "InArcIt", which can be used the same way. |
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163 | However, they also have iterator classes for edges. |
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164 | \ref concepts::Graph::EdgeIt "EdgeIt" traverses all edges in the graph and |
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165 | \ref concepts::Graph::IncEdgeIt "IncEdgeIt" lists the incident edges of a |
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166 | certain node. |
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167 | |
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168 | For example, the degree of each node can be computed and stored in a node map |
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169 | like this: |
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170 | |
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171 | \code |
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172 | ListGraph::NodeMap<int> deg(g, 0); |
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173 | for (ListGraph::NodeIt n(g); n != INVALID; ++n) { |
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174 | for (ListGraph::IncEdgeIt e(g, n); e != INVALID; ++e) { |
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175 | deg[n]++; |
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176 | } |
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177 | } |
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178 | \endcode |
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179 | |
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180 | In an undirected graph, both \ref concepts::Graph::OutArcIt "OutArcIt" |
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181 | and \ref concepts::Graph::InArcIt "InArcIt" iterates on the same \e edges |
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182 | but with opposite direction. They are convertible to both \c Arc and |
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183 | \c Edge types. \ref concepts::Graph::IncEdgeIt "IncEdgeIt" also iterates |
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184 | on these edges, but it is not convertible to \c Arc, only to \c Edge. |
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185 | |
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186 | Apart from the node and arc maps, an undirected graph also defines |
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187 | a template member class for constructing edge maps. These maps can be |
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188 | used in conjunction with both edges and arcs. |
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189 | |
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190 | For example, |
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191 | \code |
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192 | ListGraph::EdgeMap cost(g); |
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193 | cost[e] = 10; |
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194 | std::cout << cost[e] << std::endl; |
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195 | std::cout << cost[a1] << ", " << cost[a2] << std::endl; |
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196 | |
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197 | ListGraph::ArcMap arc_cost(g); |
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198 | arc_cost[a1] = cost[a1]; |
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199 | arc_cost[a2] = 2 * cost[a2]; |
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200 | // std::cout << arc_cost[e] << std::endl; // this is not valid |
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201 | std::cout << arc_cost[a1] << ", " << arc_cost[a2] << std::endl; |
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202 | \endcode |
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203 | |
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204 | [SEC]sec_special_graphs[SEC] Special Graph Structures |
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205 | |
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206 | In addition to the general undirected classes \ref ListGraph and |
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207 | \ref SmartGraph, LEMON also provides special purpose graph types for |
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208 | handling \ref FullGraph "full graphs", \ref GridGraph "grid graphs" and |
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209 | \ref HypercubeGraph "hypercube graphs". |
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210 | They all static structures, i.e. they do not allow distinct item additions |
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211 | or deletions, the graph has to be built at once. |
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212 | |
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213 | [TRAILER] |
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214 | */ |
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215 | } |
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