[1224] | 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 | #ifndef LEMON_EDMONDS_KARP_H |
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| 20 | #define LEMON_EDMONDS_KARP_H |
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| 21 | |
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| 22 | /// \file |
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| 23 | /// \ingroup max_flow |
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| 24 | /// \brief Implementation of the Edmonds-Karp algorithm. |
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| 25 | |
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| 26 | #include <lemon/tolerance.h> |
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| 27 | #include <vector> |
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| 28 | |
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| 29 | namespace lemon { |
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| 30 | |
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| 31 | /// \brief Default traits class of EdmondsKarp class. |
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| 32 | /// |
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| 33 | /// Default traits class of EdmondsKarp class. |
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| 34 | /// \param GR Digraph type. |
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| 35 | /// \param CAP Type of capacity map. |
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| 36 | template <typename GR, typename CAP> |
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| 37 | struct EdmondsKarpDefaultTraits { |
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| 38 | |
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| 39 | /// \brief The digraph type the algorithm runs on. |
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| 40 | typedef GR Digraph; |
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| 41 | |
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| 42 | /// \brief The type of the map that stores the arc capacities. |
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| 43 | /// |
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| 44 | /// The type of the map that stores the arc capacities. |
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| 45 | /// It must meet the \ref concepts::ReadMap "ReadMap" concept. |
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| 46 | typedef CAP CapacityMap; |
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| 47 | |
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[1225] | 48 | /// \brief The type of the flow values. |
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[1224] | 49 | typedef typename CapacityMap::Value Value; |
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| 50 | |
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[1225] | 51 | /// \brief The type of the map that stores the flow values. |
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[1224] | 52 | /// |
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[1225] | 53 | /// The type of the map that stores the flow values. |
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[1224] | 54 | /// It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept. |
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[1225] | 55 | #ifdef DOXYGEN |
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| 56 | typedef GR::ArcMap<Value> FlowMap; |
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| 57 | #else |
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[1224] | 58 | typedef typename Digraph::template ArcMap<Value> FlowMap; |
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[1225] | 59 | #endif |
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[1224] | 60 | |
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| 61 | /// \brief Instantiates a FlowMap. |
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| 62 | /// |
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| 63 | /// This function instantiates a \ref FlowMap. |
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[1225] | 64 | /// \param digraph The digraph for which we would like to define |
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| 65 | /// the flow map. |
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[1224] | 66 | static FlowMap* createFlowMap(const Digraph& digraph) { |
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| 67 | return new FlowMap(digraph); |
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| 68 | } |
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| 69 | |
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| 70 | /// \brief The tolerance used by the algorithm |
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| 71 | /// |
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| 72 | /// The tolerance used by the algorithm to handle inexact computation. |
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| 73 | typedef lemon::Tolerance<Value> Tolerance; |
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| 74 | |
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| 75 | }; |
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| 76 | |
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| 77 | /// \ingroup max_flow |
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| 78 | /// |
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| 79 | /// \brief Edmonds-Karp algorithms class. |
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| 80 | /// |
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| 81 | /// This class provides an implementation of the \e Edmonds-Karp \e |
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[1225] | 82 | /// algorithm producing a \ref max_flow "flow of maximum value" in a |
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| 83 | /// digraph \ref clrs01algorithms, \ref amo93networkflows, |
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| 84 | /// \ref edmondskarp72theoretical. |
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| 85 | /// The Edmonds-Karp algorithm is slower than the Preflow |
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| 86 | /// algorithm, but it has an advantage of the step-by-step execution |
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[1224] | 87 | /// control with feasible flow solutions. The \e source node, the \e |
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| 88 | /// target node, the \e capacity of the arcs and the \e starting \e |
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| 89 | /// flow value of the arcs should be passed to the algorithm |
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| 90 | /// through the constructor. |
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| 91 | /// |
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| 92 | /// The time complexity of the algorithm is \f$ O(nm^2) \f$ in |
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[1225] | 93 | /// worst case. Always try the Preflow algorithm instead of this if |
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[1224] | 94 | /// you just want to compute the optimal flow. |
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| 95 | /// |
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[1225] | 96 | /// \tparam GR The type of the digraph the algorithm runs on. |
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| 97 | /// \tparam CAP The type of the capacity map. The default map |
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| 98 | /// type is \ref concepts::Digraph::ArcMap "GR::ArcMap<int>". |
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| 99 | /// \tparam TR The traits class that defines various types used by the |
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| 100 | /// algorithm. By default, it is \ref EdmondsKarpDefaultTraits |
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| 101 | /// "EdmondsKarpDefaultTraits<GR, CAP>". |
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| 102 | /// In most cases, this parameter should not be set directly, |
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| 103 | /// consider to use the named template parameters instead. |
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[1224] | 104 | |
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| 105 | #ifdef DOXYGEN |
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| 106 | template <typename GR, typename CAP, typename TR> |
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| 107 | #else |
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| 108 | template <typename GR, |
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| 109 | typename CAP = typename GR::template ArcMap<int>, |
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| 110 | typename TR = EdmondsKarpDefaultTraits<GR, CAP> > |
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| 111 | #endif |
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| 112 | class EdmondsKarp { |
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| 113 | public: |
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| 114 | |
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[1225] | 115 | /// The \ref EdmondsKarpDefaultTraits "traits class" of the algorithm. |
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[1224] | 116 | typedef TR Traits; |
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[1225] | 117 | /// The type of the digraph the algorithm runs on. |
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[1224] | 118 | typedef typename Traits::Digraph Digraph; |
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[1225] | 119 | /// The type of the capacity map. |
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[1224] | 120 | typedef typename Traits::CapacityMap CapacityMap; |
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[1225] | 121 | /// The type of the flow values. |
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[1224] | 122 | typedef typename Traits::Value Value; |
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| 123 | |
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[1225] | 124 | /// The type of the flow map. |
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[1224] | 125 | typedef typename Traits::FlowMap FlowMap; |
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[1225] | 126 | /// The type of the tolerance. |
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[1224] | 127 | typedef typename Traits::Tolerance Tolerance; |
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| 128 | |
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| 129 | private: |
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| 130 | |
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| 131 | TEMPLATE_DIGRAPH_TYPEDEFS(Digraph); |
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| 132 | typedef typename Digraph::template NodeMap<Arc> PredMap; |
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| 133 | |
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| 134 | const Digraph& _graph; |
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| 135 | const CapacityMap* _capacity; |
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| 136 | |
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| 137 | Node _source, _target; |
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| 138 | |
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| 139 | FlowMap* _flow; |
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| 140 | bool _local_flow; |
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| 141 | |
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| 142 | PredMap* _pred; |
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| 143 | std::vector<Node> _queue; |
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| 144 | |
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| 145 | Tolerance _tolerance; |
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| 146 | Value _flow_value; |
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| 147 | |
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| 148 | void createStructures() { |
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| 149 | if (!_flow) { |
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| 150 | _flow = Traits::createFlowMap(_graph); |
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| 151 | _local_flow = true; |
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| 152 | } |
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| 153 | if (!_pred) { |
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| 154 | _pred = new PredMap(_graph); |
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| 155 | } |
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| 156 | _queue.resize(countNodes(_graph)); |
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| 157 | } |
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| 158 | |
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| 159 | void destroyStructures() { |
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| 160 | if (_local_flow) { |
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| 161 | delete _flow; |
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| 162 | } |
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| 163 | if (_pred) { |
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| 164 | delete _pred; |
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| 165 | } |
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| 166 | } |
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| 167 | |
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| 168 | public: |
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| 169 | |
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| 170 | ///\name Named template parameters |
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| 171 | |
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| 172 | ///@{ |
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| 173 | |
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| 174 | template <typename T> |
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[1226] | 175 | struct SetFlowMapTraits : public Traits { |
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[1224] | 176 | typedef T FlowMap; |
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| 177 | static FlowMap *createFlowMap(const Digraph&) { |
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[1225] | 178 | LEMON_ASSERT(false, "FlowMap is not initialized"); |
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[1224] | 179 | return 0; |
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| 180 | } |
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| 181 | }; |
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| 182 | |
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| 183 | /// \brief \ref named-templ-param "Named parameter" for setting |
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| 184 | /// FlowMap type |
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| 185 | /// |
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| 186 | /// \ref named-templ-param "Named parameter" for setting FlowMap |
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| 187 | /// type |
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| 188 | template <typename T> |
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[1226] | 189 | struct SetFlowMap |
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| 190 | : public EdmondsKarp<Digraph, CapacityMap, SetFlowMapTraits<T> > { |
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| 191 | typedef EdmondsKarp<Digraph, CapacityMap, SetFlowMapTraits<T> > Create; |
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[1224] | 192 | }; |
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| 193 | |
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| 194 | /// @} |
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| 195 | |
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| 196 | protected: |
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| 197 | |
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| 198 | EdmondsKarp() {} |
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| 199 | |
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| 200 | public: |
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| 201 | |
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| 202 | /// \brief The constructor of the class. |
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| 203 | /// |
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| 204 | /// The constructor of the class. |
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| 205 | /// \param digraph The digraph the algorithm runs on. |
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| 206 | /// \param capacity The capacity of the arcs. |
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| 207 | /// \param source The source node. |
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| 208 | /// \param target The target node. |
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| 209 | EdmondsKarp(const Digraph& digraph, const CapacityMap& capacity, |
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| 210 | Node source, Node target) |
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| 211 | : _graph(digraph), _capacity(&capacity), _source(source), _target(target), |
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| 212 | _flow(0), _local_flow(false), _pred(0), _tolerance(), _flow_value() |
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| 213 | { |
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[1225] | 214 | LEMON_ASSERT(_source != _target, |
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| 215 | "Flow source and target are the same nodes."); |
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[1224] | 216 | } |
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| 217 | |
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| 218 | /// \brief Destructor. |
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| 219 | /// |
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| 220 | /// Destructor. |
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| 221 | ~EdmondsKarp() { |
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| 222 | destroyStructures(); |
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| 223 | } |
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| 224 | |
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| 225 | /// \brief Sets the capacity map. |
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| 226 | /// |
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| 227 | /// Sets the capacity map. |
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[1225] | 228 | /// \return <tt>(*this)</tt> |
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[1224] | 229 | EdmondsKarp& capacityMap(const CapacityMap& map) { |
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| 230 | _capacity = ↦ |
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| 231 | return *this; |
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| 232 | } |
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| 233 | |
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| 234 | /// \brief Sets the flow map. |
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| 235 | /// |
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| 236 | /// Sets the flow map. |
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[1225] | 237 | /// If you don't use this function before calling \ref run() or |
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| 238 | /// \ref init(), an instance will be allocated automatically. |
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| 239 | /// The destructor deallocates this automatically allocated map, |
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| 240 | /// of course. |
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| 241 | /// \return <tt>(*this)</tt> |
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[1224] | 242 | EdmondsKarp& flowMap(FlowMap& map) { |
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| 243 | if (_local_flow) { |
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| 244 | delete _flow; |
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| 245 | _local_flow = false; |
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| 246 | } |
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| 247 | _flow = ↦ |
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| 248 | return *this; |
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| 249 | } |
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| 250 | |
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| 251 | /// \brief Sets the source node. |
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| 252 | /// |
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| 253 | /// Sets the source node. |
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[1225] | 254 | /// \return <tt>(*this)</tt> |
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[1224] | 255 | EdmondsKarp& source(const Node& node) { |
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| 256 | _source = node; |
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| 257 | return *this; |
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| 258 | } |
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| 259 | |
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| 260 | /// \brief Sets the target node. |
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| 261 | /// |
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| 262 | /// Sets the target node. |
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[1225] | 263 | /// \return <tt>(*this)</tt> |
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[1224] | 264 | EdmondsKarp& target(const Node& node) { |
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| 265 | _target = node; |
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| 266 | return *this; |
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| 267 | } |
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| 268 | |
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| 269 | /// \brief Sets the tolerance used by algorithm. |
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| 270 | /// |
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| 271 | /// Sets the tolerance used by algorithm. |
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[1225] | 272 | /// \return <tt>(*this)</tt> |
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[1224] | 273 | EdmondsKarp& tolerance(const Tolerance& tolerance) { |
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| 274 | _tolerance = tolerance; |
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| 275 | return *this; |
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| 276 | } |
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| 277 | |
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[1225] | 278 | /// \brief Returns a const reference to the tolerance. |
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[1224] | 279 | /// |
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[1225] | 280 | /// Returns a const reference to the tolerance object used by |
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| 281 | /// the algorithm. |
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[1224] | 282 | const Tolerance& tolerance() const { |
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| 283 | return _tolerance; |
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| 284 | } |
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| 285 | |
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| 286 | /// \name Execution control |
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[1225] | 287 | /// The simplest way to execute the algorithm is to use \ref run().\n |
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| 288 | /// If you need better control on the initial solution or the execution, |
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| 289 | /// you have to call one of the \ref init() functions first, then |
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| 290 | /// \ref start() or multiple times the \ref augment() function. |
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[1224] | 291 | |
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| 292 | ///@{ |
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| 293 | |
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[1225] | 294 | /// \brief Initializes the algorithm. |
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| 295 | /// |
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| 296 | /// Initializes the internal data structures and sets the initial |
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| 297 | /// flow to zero on each arc. |
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[1224] | 298 | void init() { |
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| 299 | createStructures(); |
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| 300 | for (ArcIt it(_graph); it != INVALID; ++it) { |
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| 301 | _flow->set(it, 0); |
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| 302 | } |
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| 303 | _flow_value = 0; |
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| 304 | } |
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| 305 | |
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[1225] | 306 | /// \brief Initializes the algorithm using the given flow map. |
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| 307 | /// |
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| 308 | /// Initializes the internal data structures and sets the initial |
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| 309 | /// flow to the given \c flowMap. The \c flowMap should |
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| 310 | /// contain a feasible flow, i.e. at each node excluding the source |
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| 311 | /// and the target, the incoming flow should be equal to the |
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[1224] | 312 | /// outgoing flow. |
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| 313 | template <typename FlowMap> |
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[1227] | 314 | void init(const FlowMap& flowMap) { |
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[1224] | 315 | createStructures(); |
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| 316 | for (ArcIt e(_graph); e != INVALID; ++e) { |
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| 317 | _flow->set(e, flowMap[e]); |
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| 318 | } |
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| 319 | _flow_value = 0; |
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| 320 | for (OutArcIt jt(_graph, _source); jt != INVALID; ++jt) { |
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| 321 | _flow_value += (*_flow)[jt]; |
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| 322 | } |
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| 323 | for (InArcIt jt(_graph, _source); jt != INVALID; ++jt) { |
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| 324 | _flow_value -= (*_flow)[jt]; |
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| 325 | } |
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| 326 | } |
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| 327 | |
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[1225] | 328 | /// \brief Initializes the algorithm using the given flow map. |
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| 329 | /// |
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| 330 | /// Initializes the internal data structures and sets the initial |
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| 331 | /// flow to the given \c flowMap. The \c flowMap should |
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| 332 | /// contain a feasible flow, i.e. at each node excluding the source |
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| 333 | /// and the target, the incoming flow should be equal to the |
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| 334 | /// outgoing flow. |
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| 335 | /// \return \c false when the given \c flowMap does not contain a |
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[1224] | 336 | /// feasible flow. |
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| 337 | template <typename FlowMap> |
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[1227] | 338 | bool checkedInit(const FlowMap& flowMap) { |
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[1224] | 339 | createStructures(); |
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| 340 | for (ArcIt e(_graph); e != INVALID; ++e) { |
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| 341 | _flow->set(e, flowMap[e]); |
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| 342 | } |
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| 343 | for (NodeIt it(_graph); it != INVALID; ++it) { |
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| 344 | if (it == _source || it == _target) continue; |
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| 345 | Value outFlow = 0; |
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| 346 | for (OutArcIt jt(_graph, it); jt != INVALID; ++jt) { |
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| 347 | outFlow += (*_flow)[jt]; |
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| 348 | } |
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| 349 | Value inFlow = 0; |
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| 350 | for (InArcIt jt(_graph, it); jt != INVALID; ++jt) { |
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| 351 | inFlow += (*_flow)[jt]; |
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| 352 | } |
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| 353 | if (_tolerance.different(outFlow, inFlow)) { |
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| 354 | return false; |
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| 355 | } |
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| 356 | } |
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| 357 | for (ArcIt it(_graph); it != INVALID; ++it) { |
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| 358 | if (_tolerance.less((*_flow)[it], 0)) return false; |
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| 359 | if (_tolerance.less((*_capacity)[it], (*_flow)[it])) return false; |
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| 360 | } |
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| 361 | _flow_value = 0; |
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| 362 | for (OutArcIt jt(_graph, _source); jt != INVALID; ++jt) { |
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| 363 | _flow_value += (*_flow)[jt]; |
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| 364 | } |
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| 365 | for (InArcIt jt(_graph, _source); jt != INVALID; ++jt) { |
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| 366 | _flow_value -= (*_flow)[jt]; |
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| 367 | } |
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| 368 | return true; |
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| 369 | } |
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| 370 | |
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[1225] | 371 | /// \brief Augments the solution along a shortest path. |
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[1224] | 372 | /// |
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[1225] | 373 | /// Augments the solution along a shortest path. This function searches a |
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| 374 | /// shortest path between the source and the target |
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| 375 | /// in the residual digraph by the Bfs algoritm. |
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[1224] | 376 | /// Then it increases the flow on this path with the minimal residual |
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[1225] | 377 | /// capacity on the path. If there is no such path, it gives back |
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[1224] | 378 | /// false. |
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[1225] | 379 | /// \return \c false when the augmenting did not success, i.e. the |
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[1224] | 380 | /// current flow is a feasible and optimal solution. |
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| 381 | bool augment() { |
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| 382 | for (NodeIt n(_graph); n != INVALID; ++n) { |
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| 383 | _pred->set(n, INVALID); |
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| 384 | } |
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| 385 | |
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| 386 | int first = 0, last = 1; |
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| 387 | |
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| 388 | _queue[0] = _source; |
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| 389 | _pred->set(_source, OutArcIt(_graph, _source)); |
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| 390 | |
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| 391 | while (first != last && (*_pred)[_target] == INVALID) { |
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| 392 | Node n = _queue[first++]; |
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| 393 | |
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| 394 | for (OutArcIt e(_graph, n); e != INVALID; ++e) { |
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| 395 | Value rem = (*_capacity)[e] - (*_flow)[e]; |
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| 396 | Node t = _graph.target(e); |
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| 397 | if (_tolerance.positive(rem) && (*_pred)[t] == INVALID) { |
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| 398 | _pred->set(t, e); |
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| 399 | _queue[last++] = t; |
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| 400 | } |
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| 401 | } |
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| 402 | for (InArcIt e(_graph, n); e != INVALID; ++e) { |
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| 403 | Value rem = (*_flow)[e]; |
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| 404 | Node t = _graph.source(e); |
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| 405 | if (_tolerance.positive(rem) && (*_pred)[t] == INVALID) { |
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| 406 | _pred->set(t, e); |
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| 407 | _queue[last++] = t; |
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| 408 | } |
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| 409 | } |
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| 410 | } |
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| 411 | |
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| 412 | if ((*_pred)[_target] != INVALID) { |
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| 413 | Node n = _target; |
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| 414 | Arc e = (*_pred)[n]; |
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| 415 | |
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| 416 | Value prem = (*_capacity)[e] - (*_flow)[e]; |
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| 417 | n = _graph.source(e); |
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| 418 | while (n != _source) { |
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| 419 | e = (*_pred)[n]; |
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| 420 | if (_graph.target(e) == n) { |
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| 421 | Value rem = (*_capacity)[e] - (*_flow)[e]; |
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| 422 | if (rem < prem) prem = rem; |
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| 423 | n = _graph.source(e); |
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| 424 | } else { |
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| 425 | Value rem = (*_flow)[e]; |
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| 426 | if (rem < prem) prem = rem; |
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| 427 | n = _graph.target(e); |
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| 428 | } |
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| 429 | } |
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| 430 | |
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| 431 | n = _target; |
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| 432 | e = (*_pred)[n]; |
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| 433 | |
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| 434 | _flow->set(e, (*_flow)[e] + prem); |
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| 435 | n = _graph.source(e); |
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| 436 | while (n != _source) { |
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| 437 | e = (*_pred)[n]; |
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| 438 | if (_graph.target(e) == n) { |
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| 439 | _flow->set(e, (*_flow)[e] + prem); |
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| 440 | n = _graph.source(e); |
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| 441 | } else { |
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| 442 | _flow->set(e, (*_flow)[e] - prem); |
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| 443 | n = _graph.target(e); |
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| 444 | } |
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| 445 | } |
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| 446 | |
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| 447 | _flow_value += prem; |
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| 448 | return true; |
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| 449 | } else { |
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| 450 | return false; |
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| 451 | } |
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| 452 | } |
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| 453 | |
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| 454 | /// \brief Executes the algorithm |
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| 455 | /// |
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[1225] | 456 | /// Executes the algorithm by performing augmenting phases until the |
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| 457 | /// optimal solution is reached. |
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| 458 | /// \pre One of the \ref init() functions must be called before |
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| 459 | /// using this function. |
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[1224] | 460 | void start() { |
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| 461 | while (augment()) {} |
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| 462 | } |
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| 463 | |
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| 464 | /// \brief Runs the algorithm. |
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| 465 | /// |
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[1225] | 466 | /// Runs the Edmonds-Karp algorithm. |
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| 467 | /// \note ek.run() is just a shortcut of the following code. |
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[1224] | 468 | ///\code |
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| 469 | /// ek.init(); |
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| 470 | /// ek.start(); |
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| 471 | ///\endcode |
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| 472 | void run() { |
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| 473 | init(); |
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| 474 | start(); |
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| 475 | } |
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| 476 | |
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| 477 | /// @} |
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| 478 | |
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| 479 | /// \name Query Functions |
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| 480 | /// The result of the Edmonds-Karp algorithm can be obtained using these |
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| 481 | /// functions.\n |
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[1225] | 482 | /// Either \ref run() or \ref start() should be called before using them. |
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[1224] | 483 | |
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| 484 | ///@{ |
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| 485 | |
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| 486 | /// \brief Returns the value of the maximum flow. |
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| 487 | /// |
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[1225] | 488 | /// Returns the value of the maximum flow found by the algorithm. |
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| 489 | /// |
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| 490 | /// \pre Either \ref run() or \ref init() must be called before |
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| 491 | /// using this function. |
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[1224] | 492 | Value flowValue() const { |
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| 493 | return _flow_value; |
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| 494 | } |
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| 495 | |
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[1225] | 496 | /// \brief Returns the flow value on the given arc. |
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[1224] | 497 | /// |
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[1225] | 498 | /// Returns the flow value on the given arc. |
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| 499 | /// |
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| 500 | /// \pre Either \ref run() or \ref init() must be called before |
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| 501 | /// using this function. |
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[1224] | 502 | Value flow(const Arc& arc) const { |
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| 503 | return (*_flow)[arc]; |
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| 504 | } |
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| 505 | |
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[1225] | 506 | /// \brief Returns a const reference to the flow map. |
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[1224] | 507 | /// |
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[1225] | 508 | /// Returns a const reference to the arc map storing the found flow. |
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| 509 | /// |
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| 510 | /// \pre Either \ref run() or \ref init() must be called before |
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| 511 | /// using this function. |
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| 512 | const FlowMap& flowMap() const { |
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| 513 | return *_flow; |
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| 514 | } |
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[1224] | 515 | |
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[1225] | 516 | /// \brief Returns \c true when the node is on the source side of the |
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| 517 | /// minimum cut. |
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| 518 | /// |
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| 519 | /// Returns true when the node is on the source side of the found |
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| 520 | /// minimum cut. |
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| 521 | /// |
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| 522 | /// \pre Either \ref run() or \ref init() must be called before |
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| 523 | /// using this function. |
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[1224] | 524 | bool minCut(const Node& node) const { |
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| 525 | return ((*_pred)[node] != INVALID) or node == _source; |
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| 526 | } |
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| 527 | |
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[1225] | 528 | /// \brief Gives back a minimum value cut. |
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[1224] | 529 | /// |
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[1225] | 530 | /// Sets \c cutMap to the characteristic vector of a minimum value |
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| 531 | /// cut. \c cutMap should be a \ref concepts::WriteMap "writable" |
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| 532 | /// node map with \c bool (or convertible) value type. |
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| 533 | /// |
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| 534 | /// \note This function calls \ref minCut() for each node, so it runs in |
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| 535 | /// O(n) time. |
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| 536 | /// |
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| 537 | /// \pre Either \ref run() or \ref init() must be called before |
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| 538 | /// using this function. |
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[1224] | 539 | template <typename CutMap> |
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| 540 | void minCutMap(CutMap& cutMap) const { |
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| 541 | for (NodeIt n(_graph); n != INVALID; ++n) { |
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| 542 | cutMap.set(n, (*_pred)[n] != INVALID); |
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| 543 | } |
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| 544 | cutMap.set(_source, true); |
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| 545 | } |
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| 546 | |
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| 547 | /// @} |
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| 548 | |
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| 549 | }; |
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| 550 | |
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| 551 | } |
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| 552 | |
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| 553 | #endif |
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