[1738] | 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 | Edge operator++(int) |
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| 105 | { |
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| 106 | Edge e=*this; |
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| 107 | ++(*this); |
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| 108 | return e; |
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| 109 | } |
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| 110 | }; |
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| 111 | |
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| 112 | ///Checks if the graph is Euler |
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| 113 | |
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| 114 | /// \ingroup gutils |
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| 115 | ///Checks if the graph is Euler. It works for both directed and |
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| 116 | ///undirected graphs. |
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| 117 | ///\todo What to do with the isolated points? |
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| 118 | ///\todo Test required |
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| 119 | template<class Graph> |
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| 120 | #ifdef DOXYGEN |
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| 121 | bool |
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| 122 | #else |
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| 123 | typename enable_if<typename Graph::UndirTag,bool>::type |
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| 124 | #endif |
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| 125 | euler(const Graph &g) |
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| 126 | { |
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| 127 | for(typename Graph::NodeIt n(g);n!=INVALID;++n) |
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| 128 | if(countIncEdges(g,n)%2) return false; |
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| 129 | return true; |
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| 130 | } |
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| 131 | template<class Graph> |
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| 132 | typename disable_if<typename Graph::UndirTag,bool>::type |
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[1761] | 133 | euler(const Graph &g) |
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[1738] | 134 | { |
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| 135 | for(typename Graph::NodeIt n(g);n!=INVALID;++n) |
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| 136 | if(countInEdges(g,n)!=countOutEdges(g,n)) return false; |
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| 137 | return true; |
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| 138 | } |
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| 139 | |
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| 140 | } |
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