1 | /* -*- C++ -*- |
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2 | * lemon/topology.h - Part of LEMON, a generic C++ optimization library |
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3 | * |
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4 | * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport |
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5 | * (Egervary Research Group on Combinatorial Optimization, 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 | #include<lemon/invalid.h> |
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17 | #include <list> |
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18 | |
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19 | /// \ingroup gutils |
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20 | /// \file |
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21 | /// \brief Euler tour |
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22 | /// |
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23 | ///This file provides an Euler tour iterator and ways to check |
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24 | ///if a graph is euler. |
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25 | |
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26 | |
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27 | namespace lemon { |
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28 | |
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29 | ///Euler iterator in directed graphs. |
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30 | |
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31 | /// \ingroup gutils |
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32 | ///This iterator converts to the \c Edge type of the graph and using |
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33 | ///the ++ operator it provides an Euler tour of the graph (if there exists). |
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34 | /// |
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35 | ///For example |
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36 | ///if the given graph if Euler (i.e it has only one nontrivial component |
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37 | ///and the in-degree is equal to the out-degree for all nodes), |
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38 | ///the the following code will print the edge IDs according to an |
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39 | ///Euler tour of \c g. |
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40 | ///\code |
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41 | /// for(EulerIt<ListGraph> e(g),e!=INVALID;++e) { |
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42 | /// std::cout << g.id(e) << std::eol; |
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43 | /// } |
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44 | ///\endcode |
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45 | ///If \c g is not Euler then the resulted tour will not be full or closed. |
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46 | ///\todo Test required |
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47 | template<class Graph> |
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48 | class EulerIt |
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49 | { |
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50 | typedef typename Graph::Node Node; |
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51 | typedef typename Graph::NodeIt NodeIt; |
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52 | typedef typename Graph::Edge Edge; |
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53 | typedef typename Graph::EdgeIt EdgeIt; |
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54 | typedef typename Graph::OutEdgeIt OutEdgeIt; |
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55 | typedef typename Graph::InEdgeIt InEdgeIt; |
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56 | |
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57 | const Graph &g; |
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58 | typename Graph::NodeMap<OutEdgeIt> nedge; |
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59 | std::list<Edge> euler; |
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60 | |
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61 | public: |
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62 | |
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63 | ///Constructor |
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64 | |
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65 | ///\param _g A directed graph. |
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66 | ///\param start The starting point of the tour. If it is not given |
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67 | /// tho tour will start from the first node. |
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68 | EulerIt(const Graph &_g,typename Graph::Node start=INVALID) |
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69 | : g(_g), nedge(g) |
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70 | { |
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71 | if(start==INVALID) start=NodeIt(g); |
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72 | for(NodeIt n(g);n!=INVALID;++n) nedge[n]=OutEdgeIt(g,n); |
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73 | while(nedge[start]!=INVALID) { |
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74 | euler.push_back(nedge[start]); |
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75 | Node next=g.target(nedge[start]); |
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76 | ++nedge[start]; |
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77 | start=next; |
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78 | } |
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79 | } |
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80 | |
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81 | ///Edge Conversion |
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82 | operator Edge() { return euler.empty()?INVALID:euler.front(); } |
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83 | bool operator==(Invalid) { return euler.empty(); } |
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84 | bool operator!=(Invalid) { return !euler.empty(); } |
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85 | |
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86 | ///Next edge of the tour |
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87 | EulerIt &operator++() { |
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88 | Node s=g.target(euler.front()); |
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89 | euler.pop_front(); |
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90 | //This produces a warning.Strange. |
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91 | //std::list<Edge>::iterator next=euler.begin(); |
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92 | typename std::list<Edge>::iterator next=euler.begin(); |
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93 | while(nedge[s]!=INVALID) { |
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94 | euler.insert(next,nedge[s]); |
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95 | Node n=g.target(nedge[s]); |
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96 | ++nedge[s]; |
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97 | s=n; |
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98 | } |
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99 | return *this; |
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100 | } |
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101 | ///Postfix incrementation |
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102 | |
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103 | ///\warning This gives back an Edge, not an EulerIt! |
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104 | ///\todo Is this what we want? |
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105 | Edge operator++(int) |
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106 | { |
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107 | Edge e=*this; |
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108 | ++(*this); |
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109 | return e; |
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110 | } |
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111 | }; |
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112 | |
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113 | ///Checks if the graph is Euler |
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114 | |
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115 | /// \ingroup gutils |
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116 | ///Checks if the graph is Euler. It works for both directed and |
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117 | ///undirected graphs. |
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118 | ///\todo What to do with the isolated points? |
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119 | ///\todo Test required |
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120 | template<class Graph> |
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121 | #ifdef DOXYGEN |
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122 | bool |
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123 | #else |
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124 | typename enable_if<typename Graph::UndirTag,bool>::type |
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125 | #endif |
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126 | euler(const Graph &g) |
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127 | { |
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128 | for(typename Graph::NodeIt n(g);n!=INVALID;++n) |
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129 | if(countIncEdges(g,n)%2) return false; |
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130 | return true; |
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131 | } |
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132 | template<class Graph> |
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133 | typename disable_if<typename Graph::UndirTag,bool>::type |
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134 | isEuler(const Graph &g) |
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135 | { |
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136 | for(typename Graph::NodeIt n(g);n!=INVALID;++n) |
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137 | if(countInEdges(g,n)!=countOutEdges(g,n)) return false; |
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138 | return true; |
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139 | } |
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140 | |
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141 | } |
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