/* -*- mode: C++; indent-tabs-mode: nil; -*-

  *

  * This file is a part of LEMON, a generic C++ optimization library.

  *

  * Copyright (C) 2003-2010

  * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport

  * (Egervary Research Group on Combinatorial Optimization, EGRES).

  *

  * Permission to use, modify and distribute this software is granted

  * provided that this copyright notice appears in all copies. For

  * precise terms see the accompanying LICENSE file.

  *

  * This software is provided "AS IS" with no warranty of any kind,

  * express or implied, and with no claim as to its suitability for any

  * purpose.

  *

  */

 #ifndef LEMON_EULER_H

 #define LEMON_EULER_H

 #include<lemon/core.h>

 #include<lemon/adaptors.h>

 #include<lemon/connectivity.h>

 #include <list>

 /// \ingroup graph_properties

 /// \file

 /// \brief Euler tour iterators and a function for checking the \e Eulerian

 /// property.

 ///

 ///This file provides Euler tour iterators and a function to check

 ///if a (di)graph is \e Eulerian.

 namespace lemon {

   ///Euler tour iterator for digraphs.

   /// \ingroup graph_prop

   ///This iterator provides an Euler tour (Eulerian circuit) of a \e directed

   ///graph (if there exists) and it converts to the \c Arc type of the digraph.

   ///

   ///For example, if the given digraph has an Euler tour (i.e it has only one

   ///non-trivial component and the in-degree is equal to the out-degree

   ///for all nodes), then the following code will put the arcs of \c g

   ///to the vector \c et according to an Euler tour of \c g.

   ///\code

   ///  std::vector<ListDigraph::Arc> et;

   ///  for(DiEulerIt<ListDigraph> e(g); e!=INVALID; ++e)

   ///    et.push_back(e);

   ///\endcode

   ///If \c g has no Euler tour, then the resulted walk will not be closed

   ///or not contain all arcs.

   ///\sa EulerIt

   template<typename GR>

   class DiEulerIt

   {

     typedef typename GR::Node Node;

     typedef typename GR::NodeIt NodeIt;

     typedef typename GR::Arc Arc;

     typedef typename GR::ArcIt ArcIt;

     typedef typename GR::OutArcIt OutArcIt;

     typedef typename GR::InArcIt InArcIt;

     const GR &g;

     typename GR::template NodeMap<OutArcIt> narc;

     std::list<Arc> euler;

   public:

     ///Constructor

     ///Constructor.

     ///\param gr A digraph.

     ///\param start The starting point of the tour. If it is not given,

     ///the tour will start from the first node that has an outgoing arc.

     DiEulerIt(const GR &gr, typename GR::Node start = INVALID)

       : g(gr), narc(g)

     {

       if (start==INVALID) {

         NodeIt n(g);

         while (n!=INVALID && OutArcIt(g,n)==INVALID) ++n;

         start=n;

       }

       if (start!=INVALID) {

         for (NodeIt n(g); n!=INVALID; ++n) narc[n]=OutArcIt(g,n);

         while (narc[start]!=INVALID) {

           euler.push_back(narc[start]);

           Node next=g.target(narc[start]);

           ++narc[start];

           start=next;

         }

       }

     }

     ///Arc conversion

     operator Arc() { return euler.empty()?INVALID:euler.front(); }

     ///Compare with \c INVALID

     bool operator==(Invalid) { return euler.empty(); }

     ///Compare with \c INVALID

     bool operator!=(Invalid) { return !euler.empty(); }

     ///Next arc of the tour

     ///Next arc of the tour

     ///

     DiEulerIt &operator++() {

       Node s=g.target(euler.front());

       euler.pop_front();

       typename std::list<Arc>::iterator next=euler.begin();

       while(narc[s]!=INVALID) {

         euler.insert(next,narc[s]);

         Node n=g.target(narc[s]);

         ++narc[s];

         s=n;

       }

       return *this;

     }

     ///Postfix incrementation

     /// Postfix incrementation.

     ///

     ///\warning This incrementation

     ///returns an \c Arc, not a \ref DiEulerIt, as one may

     ///expect.

     Arc operator++(int)

     {

       Arc e=*this;

       ++(*this);

       return e;

     }

   };

   ///Euler tour iterator for graphs.

   /// \ingroup graph_properties

   ///This iterator provides an Euler tour (Eulerian circuit) of an

   ///\e undirected graph (if there exists) and it converts to the \c Arc

   ///and \c Edge types of the graph.

   ///

   ///For example, if the given graph has an Euler tour (i.e it has only one

   ///non-trivial component and the degree of each node is even),

   ///the following code will print the arc IDs according to an

   ///Euler tour of \c g.

   ///\code

   ///  for(EulerIt<ListGraph> e(g); e!=INVALID; ++e) {

   ///    std::cout << g.id(Edge(e)) << std::eol;

   ///  }

   ///\endcode

   ///Although this iterator is for undirected graphs, it still returns

   ///arcs in order to indicate the direction of the tour.

   ///(But arcs convert to edges, of course.)

   ///

   ///If \c g has no Euler tour, then the resulted walk will not be closed

   ///or not contain all edges.

   template<typename GR>

   class EulerIt

   {

     typedef typename GR::Node Node;

     typedef typename GR::NodeIt NodeIt;

     typedef typename GR::Arc Arc;

     typedef typename GR::Edge Edge;

     typedef typename GR::ArcIt ArcIt;

     typedef typename GR::OutArcIt OutArcIt;

     typedef typename GR::InArcIt InArcIt;

     const GR &g;

     typename GR::template NodeMap<OutArcIt> narc;

     typename GR::template EdgeMap<bool> visited;

     std::list<Arc> euler;

   public:

     ///Constructor

     ///Constructor.

     ///\param gr A graph.

     ///\param start The starting point of the tour. If it is not given,

     ///the tour will start from the first node that has an incident edge.

     EulerIt(const GR &gr, typename GR::Node start = INVALID)

       : g(gr), narc(g), visited(g, false)

     {

       if (start==INVALID) {

         NodeIt n(g);

         while (n!=INVALID && OutArcIt(g,n)==INVALID) ++n;

         start=n;

       }

       if (start!=INVALID) {

         for (NodeIt n(g); n!=INVALID; ++n) narc[n]=OutArcIt(g,n);

         while(narc[start]!=INVALID) {

           euler.push_back(narc[start]);

           visited[narc[start]]=true;

           Node next=g.target(narc[start]);

           ++narc[start];

           start=next;

           while(narc[start]!=INVALID && visited[narc[start]]) ++narc[start];

         }

       }

     }

     ///Arc conversion

     operator Arc() const { return euler.empty()?INVALID:euler.front(); }

     ///Edge conversion

     operator Edge() const { return euler.empty()?INVALID:euler.front(); }

     ///Compare with \c INVALID

     bool operator==(Invalid) const { return euler.empty(); }

     ///Compare with \c INVALID

     bool operator!=(Invalid) const { return !euler.empty(); }

     ///Next arc of the tour

     ///Next arc of the tour

     ///

     EulerIt &operator++() {

       Node s=g.target(euler.front());

       euler.pop_front();

       typename std::list<Arc>::iterator next=euler.begin();

       while(narc[s]!=INVALID) {

         while(narc[s]!=INVALID && visited[narc[s]]) ++narc[s];

         if(narc[s]==INVALID) break;

         else {

           euler.insert(next,narc[s]);

           visited[narc[s]]=true;

           Node n=g.target(narc[s]);

           ++narc[s];

           s=n;

         }

       }

       return *this;

     }

     ///Postfix incrementation

     /// Postfix incrementation.

     ///

     ///\warning This incrementation returns an \c Arc (which converts to

     ///an \c Edge), not an \ref EulerIt, as one may expect.

     Arc operator++(int)

     {

       Arc e=*this;

       ++(*this);

       return e;

     }

   };

   ///Check if the given graph is Eulerian

   /// \ingroup graph_properties

   ///This function checks if the given graph is Eulerian.

   ///It works for both directed and undirected graphs.

   ///

   ///By definition, a digraph is called \e Eulerian if

   ///and only if it is connected and the number of incoming and outgoing

   ///arcs are the same for each node.

   ///Similarly, an undirected graph is called \e Eulerian if

   ///and only if it is connected and the number of incident edges is even

   ///for each node.

   ///

   ///\note There are (di)graphs that are not Eulerian, but still have an

   /// Euler tour, since they may contain isolated nodes.

   ///

   ///\sa DiEulerIt, EulerIt

   template<typename GR>

 #ifdef DOXYGEN

   bool

 #else

   typename enable_if<UndirectedTagIndicator<GR>,bool>::type

   eulerian(const GR &g)

   {

     for(typename GR::NodeIt n(g);n!=INVALID;++n)

       if(countIncEdges(g,n)%2) return false;

     return connected(g);

   }

   template<class GR>

   typename disable_if<UndirectedTagIndicator<GR>,bool>::type

 #endif

   eulerian(const GR &g)

   {

     for(typename GR::NodeIt n(g);n!=INVALID;++n)

       if(countInArcs(g,n)!=countOutArcs(g,n)) return false;

     return connected(undirector(g));

   }

 }

 #endif