# HG changeset patch
# User alpar
# Date 1130169518 0
# Node ID 470aa67893f5fb311ff6fa5021dfc4d0c690d7ae
# Parent  dc821d2668c191c5bd59e4f99ad97404f925cd3e
Euler tour iterator.

diff -r dc821d2668c1 -r 470aa67893f5 lemon/euler.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lemon/euler.h	Mon Oct 24 15:58:38 2005 +0000
@@ -0,0 +1,141 @@
+/* -*- C++ -*-
+ * lemon/topology.h - Part of LEMON, a generic C++ optimization library
+ *
+ * Copyright (C) 2005 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.
+ *
+ */
+#include<lemon/invalid.h>
+#include <list>
+
+/// \ingroup gutils
+/// \file
+/// \brief Euler tour
+///
+///This file provides an Euler tour iterator and ways to check
+///if a graph is euler.
+
+
+namespace lemon {
+
+  ///Euler iterator in directed graphs.
+
+  /// \ingroup gutils
+  ///This iterator converts to the \c Edge type of the graph and using
+  ///the ++ operator it provides an Euler tour of the graph (if there exists).
+  ///
+  ///For example
+  ///if the given graph if Euler (i.e it has only one nontrivial component
+  ///and the in-degree is equal to the out-degree for all nodes),
+  ///the the following code will print the edge IDs according to an
+  ///Euler tour of \c g.
+  ///\code
+  ///  for(EulerIt<ListGraph> e(g),e!=INVALID;++e) {
+  ///    std::cout << g.id(e) << std::eol;
+  ///  }
+  ///\endcode
+  ///If \c g is not Euler then the resulted tour will not be full or closed.
+  ///\todo Test required
+  template<class Graph>
+  class EulerIt 
+  {
+    typedef typename Graph::Node Node;
+    typedef typename Graph::NodeIt NodeIt;
+    typedef typename Graph::Edge Edge;
+    typedef typename Graph::EdgeIt EdgeIt;
+    typedef typename Graph::OutEdgeIt OutEdgeIt;
+    typedef typename Graph::InEdgeIt InEdgeIt;
+    
+    const Graph &g;
+    typename Graph::NodeMap<OutEdgeIt> nedge;
+    std::list<Edge> euler;
+
+  public:
+    
+    ///Constructor
+
+    ///\param _g A directed graph.
+    ///\param start The starting point of the tour. If it is not given
+    ///       tho tour will start from the first node.
+    EulerIt(const Graph &_g,typename Graph::Node start=INVALID)
+      : g(_g), nedge(g)
+    {
+      if(start==INVALID) start=NodeIt(g);
+      for(NodeIt n(g);n!=INVALID;++n) nedge[n]=OutEdgeIt(g,n);
+      while(nedge[start]!=INVALID) {
+	euler.push_back(nedge[start]);
+	Node next=g.target(nedge[start]);
+	++nedge[start];
+	start=next;
+      }
+    }
+    
+    ///Edge Conversion
+    operator Edge() { return euler.empty()?INVALID:euler.front(); }
+    bool operator==(Invalid) { return euler.empty(); }
+    bool operator!=(Invalid) { return !euler.empty(); }
+    
+    ///Next edge of the tour
+    EulerIt &operator++() {
+      Node s=g.target(euler.front());
+      euler.pop_front();
+      //This produces a warning.Strange.
+      //std::list<Edge>::iterator next=euler.begin();
+      typename std::list<Edge>::iterator next=euler.begin();
+      while(nedge[s]!=INVALID) {
+	euler.insert(next,nedge[s]);
+	Node n=g.target(nedge[s]);
+	++nedge[s];
+	s=n;
+      }
+      return *this;
+    }
+    ///Postfix incrementation
+    
+    ///\warning This gives back an Edge, not an EulerIt!
+    ///\todo Is this what we want?
+    Edge operator++(int) 
+    {
+      Edge e=*this;
+      ++(*this);
+      return e;
+    }
+  };
+
+  ///Checks if the graph is Euler
+
+  /// \ingroup gutils
+  ///Checks if the graph is Euler. It works for both directed and
+  ///undirected graphs.
+  ///\todo What to do with the isolated points?
+  ///\todo Test required
+  template<class Graph>
+#ifdef DOXYGEN
+  bool
+#else
+  typename enable_if<typename Graph::UndirTag,bool>::type
+#endif
+  euler(const Graph &g) 
+  {
+    for(typename Graph::NodeIt n(g);n!=INVALID;++n)
+      if(countIncEdges(g,n)%2) return false;
+    return true;
+  }
+  template<class Graph>
+  typename disable_if<typename Graph::UndirTag,bool>::type
+  isEuler(const Graph &g) 
+  {
+    for(typename Graph::NodeIt n(g);n!=INVALID;++n)
+      if(countInEdges(g,n)!=countOutEdges(g,n)) return false;
+    return true;
+  }
+  
+}