alpar@357: /* -*- C++ -*-
alpar@357:  *
alpar@357:  * This file is a part of LEMON, a generic C++ optimization library
alpar@357:  *
alpar@357:  * Copyright (C) 2003-2008
alpar@357:  * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
alpar@357:  * (Egervary Research Group on Combinatorial Optimization, EGRES).
alpar@357:  *
alpar@357:  * Permission to use, modify and distribute this software is granted
alpar@357:  * provided that this copyright notice appears in all copies. For
alpar@357:  * precise terms see the accompanying LICENSE file.
alpar@357:  *
alpar@357:  * This software is provided "AS IS" with no warranty of any kind,
alpar@357:  * express or implied, and with no claim as to its suitability for any
alpar@357:  * purpose.
alpar@357:  *
alpar@357:  */
alpar@357: 
alpar@357: #ifndef LEMON_SUURBALLE_H
alpar@357: #define LEMON_SUURBALLE_H
alpar@357: 
alpar@357: ///\ingroup shortest_path
alpar@357: ///\file
alpar@357: ///\brief An algorithm for finding arc-disjoint paths between two
alpar@357: /// nodes having minimum total length.
alpar@357: 
alpar@357: #include <vector>
alpar@357: #include <lemon/bin_heap.h>
alpar@357: #include <lemon/path.h>
alpar@357: 
alpar@357: namespace lemon {
alpar@357: 
alpar@357:   /// \addtogroup shortest_path
alpar@357:   /// @{
alpar@357: 
kpeter@358:   /// \brief Algorithm for finding arc-disjoint paths between two nodes
kpeter@358:   /// having minimum total length.
alpar@357:   ///
alpar@357:   /// \ref lemon::Suurballe "Suurballe" implements an algorithm for
alpar@357:   /// finding arc-disjoint paths having minimum total length (cost)
kpeter@358:   /// from a given source node to a given target node in a digraph.
alpar@357:   ///
alpar@357:   /// In fact, this implementation is the specialization of the
alpar@357:   /// \ref CapacityScaling "successive shortest path" algorithm.
alpar@357:   ///
kpeter@358:   /// \tparam Digraph The digraph type the algorithm runs on.
kpeter@358:   /// The default value is \c ListDigraph.
alpar@357:   /// \tparam LengthMap The type of the length (cost) map.
kpeter@358:   /// The default value is <tt>Digraph::ArcMap<int></tt>.
alpar@357:   ///
alpar@357:   /// \warning Length values should be \e non-negative \e integers.
alpar@357:   ///
alpar@357:   /// \note For finding node-disjoint paths this algorithm can be used
alpar@357:   /// with \ref SplitDigraphAdaptor.
kpeter@358: #ifdef DOXYGEN
kpeter@358:   template <typename Digraph, typename LengthMap>
kpeter@358: #else
kpeter@358:   template < typename Digraph = ListDigraph,
alpar@357:              typename LengthMap = typename Digraph::template ArcMap<int> >
kpeter@358: #endif
alpar@357:   class Suurballe
alpar@357:   {
alpar@357:     TEMPLATE_DIGRAPH_TYPEDEFS(Digraph);
alpar@357: 
alpar@357:     typedef typename LengthMap::Value Length;
alpar@357:     typedef ConstMap<Arc, int> ConstArcMap;
alpar@357:     typedef typename Digraph::template NodeMap<Arc> PredMap;
alpar@357: 
alpar@357:   public:
alpar@357: 
alpar@357:     /// The type of the flow map.
alpar@357:     typedef typename Digraph::template ArcMap<int> FlowMap;
alpar@357:     /// The type of the potential map.
alpar@357:     typedef typename Digraph::template NodeMap<Length> PotentialMap;
alpar@357:     /// The type of the path structures.
alpar@357:     typedef SimplePath<Digraph> Path;
alpar@357: 
alpar@357:   private:
alpar@357:   
kpeter@358:     /// \brief Special implementation of the Dijkstra algorithm
alpar@357:     /// for finding shortest paths in the residual network.
alpar@357:     ///
alpar@357:     /// \ref ResidualDijkstra is a special implementation of the
alpar@357:     /// \ref Dijkstra algorithm for finding shortest paths in the
alpar@357:     /// residual network of the digraph with respect to the reduced arc
alpar@357:     /// lengths and modifying the node potentials according to the
alpar@357:     /// distance of the nodes.
alpar@357:     class ResidualDijkstra
alpar@357:     {
alpar@357:       typedef typename Digraph::template NodeMap<int> HeapCrossRef;
alpar@357:       typedef BinHeap<Length, HeapCrossRef> Heap;
alpar@357: 
alpar@357:     private:
alpar@357: 
kpeter@358:       // The digraph the algorithm runs on
alpar@357:       const Digraph &_graph;
alpar@357: 
alpar@357:       // The main maps
alpar@357:       const FlowMap &_flow;
alpar@357:       const LengthMap &_length;
alpar@357:       PotentialMap &_potential;
alpar@357: 
alpar@357:       // The distance map
alpar@357:       PotentialMap _dist;
alpar@357:       // The pred arc map
alpar@357:       PredMap &_pred;
alpar@357:       // The processed (i.e. permanently labeled) nodes
alpar@357:       std::vector<Node> _proc_nodes;
alpar@357:       
alpar@357:       Node _s;
alpar@357:       Node _t;
alpar@357: 
alpar@357:     public:
alpar@357: 
alpar@357:       /// Constructor.
alpar@357:       ResidualDijkstra( const Digraph &digraph,
alpar@357:                         const FlowMap &flow,
alpar@357:                         const LengthMap &length,
alpar@357:                         PotentialMap &potential,
alpar@357:                         PredMap &pred,
alpar@357:                         Node s, Node t ) :
alpar@357:         _graph(digraph), _flow(flow), _length(length), _potential(potential),
alpar@357:         _dist(digraph), _pred(pred), _s(s), _t(t) {}
alpar@357: 
kpeter@358:       /// \brief Run the algorithm. It returns \c true if a path is found
alpar@357:       /// from the source node to the target node.
alpar@357:       bool run() {
alpar@357:         HeapCrossRef heap_cross_ref(_graph, Heap::PRE_HEAP);
alpar@357:         Heap heap(heap_cross_ref);
alpar@357:         heap.push(_s, 0);
alpar@357:         _pred[_s] = INVALID;
alpar@357:         _proc_nodes.clear();
alpar@357: 
kpeter@358:         // Process nodes
alpar@357:         while (!heap.empty() && heap.top() != _t) {
alpar@357:           Node u = heap.top(), v;
alpar@357:           Length d = heap.prio() + _potential[u], nd;
alpar@357:           _dist[u] = heap.prio();
alpar@357:           heap.pop();
alpar@357:           _proc_nodes.push_back(u);
alpar@357: 
kpeter@358:           // Traverse outgoing arcs
alpar@357:           for (OutArcIt e(_graph, u); e != INVALID; ++e) {
alpar@357:             if (_flow[e] == 0) {
alpar@357:               v = _graph.target(e);
alpar@357:               switch(heap.state(v)) {
alpar@357:               case Heap::PRE_HEAP:
alpar@357:                 heap.push(v, d + _length[e] - _potential[v]);
alpar@357:                 _pred[v] = e;
alpar@357:                 break;
alpar@357:               case Heap::IN_HEAP:
alpar@357:                 nd = d + _length[e] - _potential[v];
alpar@357:                 if (nd < heap[v]) {
alpar@357:                   heap.decrease(v, nd);
alpar@357:                   _pred[v] = e;
alpar@357:                 }
alpar@357:                 break;
alpar@357:               case Heap::POST_HEAP:
alpar@357:                 break;
alpar@357:               }
alpar@357:             }
alpar@357:           }
alpar@357: 
kpeter@358:           // Traverse incoming arcs
alpar@357:           for (InArcIt e(_graph, u); e != INVALID; ++e) {
alpar@357:             if (_flow[e] == 1) {
alpar@357:               v = _graph.source(e);
alpar@357:               switch(heap.state(v)) {
alpar@357:               case Heap::PRE_HEAP:
alpar@357:                 heap.push(v, d - _length[e] - _potential[v]);
alpar@357:                 _pred[v] = e;
alpar@357:                 break;
alpar@357:               case Heap::IN_HEAP:
alpar@357:                 nd = d - _length[e] - _potential[v];
alpar@357:                 if (nd < heap[v]) {
alpar@357:                   heap.decrease(v, nd);
alpar@357:                   _pred[v] = e;
alpar@357:                 }
alpar@357:                 break;
alpar@357:               case Heap::POST_HEAP:
alpar@357:                 break;
alpar@357:               }
alpar@357:             }
alpar@357:           }
alpar@357:         }
alpar@357:         if (heap.empty()) return false;
alpar@357: 
kpeter@358:         // Update potentials of processed nodes
alpar@357:         Length t_dist = heap.prio();
alpar@357:         for (int i = 0; i < int(_proc_nodes.size()); ++i)
alpar@357:           _potential[_proc_nodes[i]] += _dist[_proc_nodes[i]] - t_dist;
alpar@357:         return true;
alpar@357:       }
alpar@357: 
alpar@357:     }; //class ResidualDijkstra
alpar@357: 
alpar@357:   private:
alpar@357: 
kpeter@358:     // The digraph the algorithm runs on
alpar@357:     const Digraph &_graph;
alpar@357:     // The length map
alpar@357:     const LengthMap &_length;
alpar@357:     
alpar@357:     // Arc map of the current flow
alpar@357:     FlowMap *_flow;
alpar@357:     bool _local_flow;
alpar@357:     // Node map of the current potentials
alpar@357:     PotentialMap *_potential;
alpar@357:     bool _local_potential;
alpar@357: 
alpar@357:     // The source node
alpar@357:     Node _source;
alpar@357:     // The target node
alpar@357:     Node _target;
alpar@357: 
alpar@357:     // Container to store the found paths
alpar@357:     std::vector< SimplePath<Digraph> > paths;
alpar@357:     int _path_num;
alpar@357: 
alpar@357:     // The pred arc map
alpar@357:     PredMap _pred;
alpar@357:     // Implementation of the Dijkstra algorithm for finding augmenting
alpar@357:     // shortest paths in the residual network
alpar@357:     ResidualDijkstra *_dijkstra;
alpar@357: 
alpar@357:   public:
alpar@357: 
alpar@357:     /// \brief Constructor.
alpar@357:     ///
alpar@357:     /// Constructor.
alpar@357:     ///
kpeter@358:     /// \param digraph The digraph the algorithm runs on.
alpar@357:     /// \param length The length (cost) values of the arcs.
alpar@357:     /// \param s The source node.
alpar@357:     /// \param t The target node.
alpar@357:     Suurballe( const Digraph &digraph,
alpar@357:                const LengthMap &length,
alpar@357:                Node s, Node t ) :
alpar@357:       _graph(digraph), _length(length), _flow(0), _local_flow(false),
alpar@357:       _potential(0), _local_potential(false), _source(s), _target(t),
alpar@357:       _pred(digraph) {}
alpar@357: 
alpar@357:     /// Destructor.
alpar@357:     ~Suurballe() {
alpar@357:       if (_local_flow) delete _flow;
alpar@357:       if (_local_potential) delete _potential;
alpar@357:       delete _dijkstra;
alpar@357:     }
alpar@357: 
kpeter@358:     /// \brief Set the flow map.
alpar@357:     ///
kpeter@358:     /// This function sets the flow map.
alpar@357:     ///
alpar@357:     /// The found flow contains only 0 and 1 values. It is the union of
alpar@357:     /// the found arc-disjoint paths.
alpar@357:     ///
alpar@357:     /// \return \c (*this)
alpar@357:     Suurballe& flowMap(FlowMap &map) {
alpar@357:       if (_local_flow) {
alpar@357:         delete _flow;
alpar@357:         _local_flow = false;
alpar@357:       }
alpar@357:       _flow = &map;
alpar@357:       return *this;
alpar@357:     }
alpar@357: 
kpeter@358:     /// \brief Set the potential map.
alpar@357:     ///
kpeter@358:     /// This function sets the potential map.
alpar@357:     ///
alpar@357:     /// The potentials provide the dual solution of the underlying 
alpar@357:     /// minimum cost flow problem.
alpar@357:     ///
alpar@357:     /// \return \c (*this)
alpar@357:     Suurballe& potentialMap(PotentialMap &map) {
alpar@357:       if (_local_potential) {
alpar@357:         delete _potential;
alpar@357:         _local_potential = false;
alpar@357:       }
alpar@357:       _potential = &map;
alpar@357:       return *this;
alpar@357:     }
alpar@357: 
alpar@357:     /// \name Execution control
alpar@357:     /// The simplest way to execute the algorithm is to call the run()
alpar@357:     /// function.
alpar@357:     /// \n
alpar@357:     /// If you only need the flow that is the union of the found
alpar@357:     /// arc-disjoint paths, you may call init() and findFlow().
alpar@357: 
alpar@357:     /// @{
alpar@357: 
kpeter@358:     /// \brief Run the algorithm.
alpar@357:     ///
kpeter@358:     /// This function runs the algorithm.
alpar@357:     ///
alpar@357:     /// \param k The number of paths to be found.
alpar@357:     ///
kpeter@358:     /// \return \c k if there are at least \c k arc-disjoint paths from
kpeter@358:     /// \c s to \c t in the digraph. Otherwise it returns the number of
alpar@357:     /// arc-disjoint paths found.
alpar@357:     ///
alpar@357:     /// \note Apart from the return value, <tt>s.run(k)</tt> is just a
alpar@357:     /// shortcut of the following code.
alpar@357:     /// \code
alpar@357:     ///   s.init();
alpar@357:     ///   s.findFlow(k);
alpar@357:     ///   s.findPaths();
alpar@357:     /// \endcode
alpar@357:     int run(int k = 2) {
alpar@357:       init();
alpar@357:       findFlow(k);
alpar@357:       findPaths();
alpar@357:       return _path_num;
alpar@357:     }
alpar@357: 
kpeter@358:     /// \brief Initialize the algorithm.
alpar@357:     ///
kpeter@358:     /// This function initializes the algorithm.
alpar@357:     void init() {
kpeter@358:       // Initialize maps
alpar@357:       if (!_flow) {
alpar@357:         _flow = new FlowMap(_graph);
alpar@357:         _local_flow = true;
alpar@357:       }
alpar@357:       if (!_potential) {
alpar@357:         _potential = new PotentialMap(_graph);
alpar@357:         _local_potential = true;
alpar@357:       }
alpar@357:       for (ArcIt e(_graph); e != INVALID; ++e) (*_flow)[e] = 0;
alpar@357:       for (NodeIt n(_graph); n != INVALID; ++n) (*_potential)[n] = 0;
alpar@357: 
alpar@357:       _dijkstra = new ResidualDijkstra( _graph, *_flow, _length, 
alpar@357:                                         *_potential, _pred,
alpar@357:                                         _source, _target );
alpar@357:     }
alpar@357: 
kpeter@358:     /// \brief Execute the successive shortest path algorithm to find
alpar@357:     /// an optimal flow.
alpar@357:     ///
kpeter@358:     /// This function executes the successive shortest path algorithm to
kpeter@358:     /// find a minimum cost flow, which is the union of \c k or less
alpar@357:     /// arc-disjoint paths.
alpar@357:     ///
kpeter@358:     /// \return \c k if there are at least \c k arc-disjoint paths from
kpeter@358:     /// \c s to \c t in the digraph. Otherwise it returns the number of
alpar@357:     /// arc-disjoint paths found.
alpar@357:     ///
alpar@357:     /// \pre \ref init() must be called before using this function.
alpar@357:     int findFlow(int k = 2) {
kpeter@358:       // Find shortest paths
alpar@357:       _path_num = 0;
alpar@357:       while (_path_num < k) {
kpeter@358:         // Run Dijkstra
alpar@357:         if (!_dijkstra->run()) break;
alpar@357:         ++_path_num;
alpar@357: 
kpeter@358:         // Set the flow along the found shortest path
alpar@357:         Node u = _target;
alpar@357:         Arc e;
alpar@357:         while ((e = _pred[u]) != INVALID) {
alpar@357:           if (u == _graph.target(e)) {
alpar@357:             (*_flow)[e] = 1;
alpar@357:             u = _graph.source(e);
alpar@357:           } else {
alpar@357:             (*_flow)[e] = 0;
alpar@357:             u = _graph.target(e);
alpar@357:           }
alpar@357:         }
alpar@357:       }
alpar@357:       return _path_num;
alpar@357:     }
alpar@357:     
kpeter@358:     /// \brief Compute the paths from the flow.
alpar@357:     ///
kpeter@358:     /// This function computes the paths from the flow.
alpar@357:     ///
alpar@357:     /// \pre \ref init() and \ref findFlow() must be called before using
alpar@357:     /// this function.
alpar@357:     void findPaths() {
kpeter@358:       // Create the residual flow map (the union of the paths not found
kpeter@358:       // so far)
alpar@357:       FlowMap res_flow(_graph);
kpeter@358:       for(ArcIt a(_graph); a != INVALID; ++a) res_flow[a] = (*_flow)[a];
alpar@357: 
alpar@357:       paths.clear();
alpar@357:       paths.resize(_path_num);
alpar@357:       for (int i = 0; i < _path_num; ++i) {
alpar@357:         Node n = _source;
alpar@357:         while (n != _target) {
alpar@357:           OutArcIt e(_graph, n);
alpar@357:           for ( ; res_flow[e] == 0; ++e) ;
alpar@357:           n = _graph.target(e);
alpar@357:           paths[i].addBack(e);
alpar@357:           res_flow[e] = 0;
alpar@357:         }
alpar@357:       }
alpar@357:     }
alpar@357: 
alpar@357:     /// @}
alpar@357: 
alpar@357:     /// \name Query Functions
kpeter@358:     /// The results of the algorithm can be obtained using these
alpar@357:     /// functions.
alpar@357:     /// \n The algorithm should be executed before using them.
alpar@357: 
alpar@357:     /// @{
alpar@357: 
kpeter@358:     /// \brief Return a const reference to the arc map storing the
alpar@357:     /// found flow.
alpar@357:     ///
kpeter@358:     /// This function returns a const reference to the arc map storing
kpeter@358:     /// the flow that is the union of the found arc-disjoint paths.
alpar@357:     ///
kpeter@358:     /// \pre \ref run() or \ref findFlow() must be called before using
kpeter@358:     /// this function.
alpar@357:     const FlowMap& flowMap() const {
alpar@357:       return *_flow;
alpar@357:     }
alpar@357: 
kpeter@358:     /// \brief Return a const reference to the node map storing the
alpar@357:     /// found potentials (the dual solution).
alpar@357:     ///
kpeter@358:     /// This function returns a const reference to the node map storing
kpeter@358:     /// the found potentials that provide the dual solution of the
kpeter@358:     /// underlying minimum cost flow problem.
alpar@357:     ///
kpeter@358:     /// \pre \ref run() or \ref findFlow() must be called before using
kpeter@358:     /// this function.
alpar@357:     const PotentialMap& potentialMap() const {
alpar@357:       return *_potential;
alpar@357:     }
alpar@357: 
kpeter@358:     /// \brief Return the flow on the given arc.
alpar@357:     ///
kpeter@358:     /// This function returns the flow on the given arc.
alpar@357:     /// It is \c 1 if the arc is involved in one of the found paths,
alpar@357:     /// otherwise it is \c 0.
alpar@357:     ///
kpeter@358:     /// \pre \ref run() or \ref findFlow() must be called before using
kpeter@358:     /// this function.
alpar@357:     int flow(const Arc& arc) const {
alpar@357:       return (*_flow)[arc];
alpar@357:     }
alpar@357: 
kpeter@358:     /// \brief Return the potential of the given node.
alpar@357:     ///
kpeter@358:     /// This function returns the potential of the given node.
alpar@357:     ///
kpeter@358:     /// \pre \ref run() or \ref findFlow() must be called before using
kpeter@358:     /// this function.
alpar@357:     Length potential(const Node& node) const {
alpar@357:       return (*_potential)[node];
alpar@357:     }
alpar@357: 
kpeter@358:     /// \brief Return the total length (cost) of the found paths (flow).
alpar@357:     ///
kpeter@358:     /// This function returns the total length (cost) of the found paths
kpeter@358:     /// (flow). The complexity of the function is \f$ O(e) \f$.
alpar@357:     ///
kpeter@358:     /// \pre \ref run() or \ref findFlow() must be called before using
kpeter@358:     /// this function.
alpar@357:     Length totalLength() const {
alpar@357:       Length c = 0;
alpar@357:       for (ArcIt e(_graph); e != INVALID; ++e)
alpar@357:         c += (*_flow)[e] * _length[e];
alpar@357:       return c;
alpar@357:     }
alpar@357: 
kpeter@358:     /// \brief Return the number of the found paths.
alpar@357:     ///
kpeter@358:     /// This function returns the number of the found paths.
alpar@357:     ///
kpeter@358:     /// \pre \ref run() or \ref findFlow() must be called before using
kpeter@358:     /// this function.
alpar@357:     int pathNum() const {
alpar@357:       return _path_num;
alpar@357:     }
alpar@357: 
kpeter@358:     /// \brief Return a const reference to the specified path.
alpar@357:     ///
kpeter@358:     /// This function returns a const reference to the specified path.
alpar@357:     ///
alpar@357:     /// \param i The function returns the \c i-th path.
alpar@357:     /// \c i must be between \c 0 and <tt>%pathNum()-1</tt>.
alpar@357:     ///
kpeter@358:     /// \pre \ref run() or \ref findPaths() must be called before using
kpeter@358:     /// this function.
alpar@357:     Path path(int i) const {
alpar@357:       return paths[i];
alpar@357:     }
alpar@357: 
alpar@357:     /// @}
alpar@357: 
alpar@357:   }; //class Suurballe
alpar@357: 
alpar@357:   ///@}
alpar@357: 
alpar@357: } //namespace lemon
alpar@357: 
alpar@357: #endif //LEMON_SUURBALLE_H