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+/* -*- C++ -*-
+ *
+ * This file is a part of LEMON, a generic C++ optimization library
+ *
+ * Copyright (C) 2003-2008
+ * 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_UNION_FIND_H
+#define LEMON_UNION_FIND_H
+
+//!\ingroup auxdat
+//!\file
+//!\brief Union-Find data structures.
+//!
+
+#include <vector>
+#include <list>
+#include <utility>
+#include <algorithm>
+#include <functional>
+
+#include <lemon/bits/invalid.h>
+
+namespace lemon {
+
+  /// \ingroup auxdat
+  ///
+  /// \brief A \e Union-Find data structure implementation
+  ///
+  /// The class implements the \e Union-Find data structure. 
+  /// The union operation uses rank heuristic, while
+  /// the find operation uses path compression.
+  /// This is a very simple but efficient implementation, providing 
+  /// only four methods: join (union), find, insert and size.
+  /// For more features see the \ref UnionFindEnum class.
+  ///
+  /// It is primarily used in Kruskal algorithm for finding minimal
+  /// cost spanning tree in a graph.
+  /// \sa kruskal()
+  ///
+  /// \pre You need to add all the elements by the \ref insert()
+  /// method.  
+  template <typename _ItemIntMap>
+  class UnionFind {
+  public:
+
+    typedef _ItemIntMap ItemIntMap;
+    typedef typename ItemIntMap::Key Item;
+
+  private:
+    // If the items vector stores negative value for an item then
+    // that item is root item and it has -items[it] component size.
+    // Else the items[it] contains the index of the parent.
+    std::vector<int> items;
+    ItemIntMap& index;
+
+    bool rep(int idx) const {
+      return items[idx] < 0;
+    }
+
+    int repIndex(int idx) const {
+      int k = idx;
+      while (!rep(k)) {
+        k = items[k] ;
+      }
+      while (idx != k) {
+        int next = items[idx];
+        const_cast<int&>(items[idx]) = k;
+        idx = next;
+      }
+      return k;
+    }
+
+  public:
+
+    /// \brief Constructor
+    ///
+    /// Constructor of the UnionFind class. You should give an item to
+    /// integer map which will be used from the data structure. If you
+    /// modify directly this map that may cause segmentation fault,
+    /// invalid data structure, or infinite loop when you use again
+    /// the union-find.
+    UnionFind(ItemIntMap& m) : index(m) {}
+
+    /// \brief Returns the index of the element's component.
+    ///
+    /// The method returns the index of the element's component.
+    /// This is an integer between zero and the number of inserted elements.
+    ///
+    int find(const Item& a) {
+      return repIndex(index[a]);
+    }
+
+    /// \brief Clears the union-find data structure
+    ///
+    /// Erase each item from the data structure.
+    void clear() {
+      items.clear();
+    }
+
+    /// \brief Inserts a new element into the structure.
+    ///
+    /// This method inserts a new element into the data structure. 
+    ///
+    /// The method returns the index of the new component.
+    int insert(const Item& a) {
+      int n = items.size();
+      items.push_back(-1);
+      index.set(a,n);
+      return n;
+    }
+
+    /// \brief Joining the components of element \e a and element \e b.
+    ///
+    /// This is the \e union operation of the Union-Find structure. 
+    /// Joins the component of element \e a and component of
+    /// element \e b. If \e a and \e b are in the same component then
+    /// it returns false otherwise it returns true.
+    bool join(const Item& a, const Item& b) {
+      int ka = repIndex(index[a]);
+      int kb = repIndex(index[b]);
+
+      if ( ka == kb ) 
+	return false;
+
+      if (items[ka] < items[kb]) {
+	items[ka] += items[kb];
+	items[kb] = ka;
+      } else {
+	items[kb] += items[ka];
+	items[ka] = kb;
+      }
+      return true;
+    }
+
+    /// \brief Returns the size of the component of element \e a.
+    ///
+    /// Returns the size of the component of element \e a.
+    int size(const Item& a) {
+      int k = repIndex(index[a]);
+      return - items[k];
+    }
+
+  };
+
+  /// \ingroup auxdat
+  ///
+  /// \brief A \e Union-Find data structure implementation which
+  /// is able to enumerate the components.
+  ///
+  /// The class implements a \e Union-Find data structure
+  /// which is able to enumerate the components and the items in
+  /// a component. If you don't need this feature then perhaps it's
+  /// better to use the \ref UnionFind class which is more efficient.
+  ///
+  /// The union operation uses rank heuristic, while
+  /// the find operation uses path compression.
+  ///
+  /// \pre You need to add all the elements by the \ref insert()
+  /// method.
+  ///
+  template <typename _ItemIntMap>
+  class UnionFindEnum {
+  public:
+    
+    typedef _ItemIntMap ItemIntMap;
+    typedef typename ItemIntMap::Key Item;
+
+  private:
+    
+    ItemIntMap& index;
+
+    // If the parent stores negative value for an item then that item
+    // is root item and it has ~(items[it].parent) component id.  Else
+    // the items[it].parent contains the index of the parent.
+    //
+    // The \c next and \c prev provides the double-linked
+    // cyclic list of one component's items.
+    struct ItemT {
+      int parent;
+      Item item;
+
+      int next, prev;
+    };
+
+    std::vector<ItemT> items;
+    int firstFreeItem;
+
+    struct ClassT {
+      int size;
+      int firstItem;
+      int next, prev;
+    };
+    
+    std::vector<ClassT> classes;
+    int firstClass, firstFreeClass;
+
+    int newClass() {
+      if (firstFreeClass == -1) {
+	int cdx = classes.size();
+	classes.push_back(ClassT());
+	return cdx;
+      } else {
+	int cdx = firstFreeClass;
+	firstFreeClass = classes[firstFreeClass].next;
+	return cdx;
+      }
+    }
+
+    int newItem() {
+      if (firstFreeItem == -1) {
+	int idx = items.size();
+	items.push_back(ItemT());
+	return idx;
+      } else {
+	int idx = firstFreeItem;
+	firstFreeItem = items[firstFreeItem].next;
+	return idx;
+      }
+    }
+
+
+    bool rep(int idx) const {
+      return items[idx].parent < 0;
+    }
+
+    int repIndex(int idx) const {
+      int k = idx;
+      while (!rep(k)) {
+        k = items[k].parent;
+      }
+      while (idx != k) {
+        int next = items[idx].parent;
+        const_cast<int&>(items[idx].parent) = k;
+        idx = next;
+      }
+      return k;
+    }
+
+    int classIndex(int idx) const {
+      return ~(items[repIndex(idx)].parent);
+    }
+
+    void singletonItem(int idx) {
+      items[idx].next = idx;
+      items[idx].prev = idx;
+    }
+
+    void laceItem(int idx, int rdx) {
+      items[idx].prev = rdx;
+      items[idx].next = items[rdx].next;
+      items[items[rdx].next].prev = idx;
+      items[rdx].next = idx;
+    }
+
+    void unlaceItem(int idx) {
+      items[items[idx].prev].next = items[idx].next;
+      items[items[idx].next].prev = items[idx].prev;
+      
+      items[idx].next = firstFreeItem;
+      firstFreeItem = idx;
+    }
+
+    void spliceItems(int ak, int bk) {
+      items[items[ak].prev].next = bk;
+      items[items[bk].prev].next = ak;
+      int tmp = items[ak].prev;
+      items[ak].prev = items[bk].prev;
+      items[bk].prev = tmp;
+        
+    }
+
+    void laceClass(int cls) {
+      if (firstClass != -1) {
+        classes[firstClass].prev = cls;
+      }
+      classes[cls].next = firstClass;
+      classes[cls].prev = -1;
+      firstClass = cls;
+    } 
+
+    void unlaceClass(int cls) {
+      if (classes[cls].prev != -1) {
+        classes[classes[cls].prev].next = classes[cls].next;
+      } else {
+        firstClass = classes[cls].next;
+      }
+      if (classes[cls].next != -1) {
+        classes[classes[cls].next].prev = classes[cls].prev;
+      }
+      
+      classes[cls].next = firstFreeClass;
+      firstFreeClass = cls;
+    } 
+
+  public:
+
+    UnionFindEnum(ItemIntMap& _index) 
+      : index(_index), items(), firstFreeItem(-1), 
+	firstClass(-1), firstFreeClass(-1) {}
+    
+    /// \brief Inserts the given element into a new component.
+    ///
+    /// This method creates a new component consisting only of the
+    /// given element.
+    ///
+    int insert(const Item& item) {
+      int idx = newItem();
+
+      index.set(item, idx);
+
+      singletonItem(idx);
+      items[idx].item = item;
+
+      int cdx = newClass();
+
+      items[idx].parent = ~cdx;
+
+      laceClass(cdx);
+      classes[cdx].size = 1;
+      classes[cdx].firstItem = idx;
+
+      firstClass = cdx;
+      
+      return cdx;
+    }
+
+    /// \brief Inserts the given element into the component of the others.
+    ///
+    /// This methods inserts the element \e a into the component of the
+    /// element \e comp. 
+    void insert(const Item& item, int cls) {
+      int rdx = classes[cls].firstItem;
+      int idx = newItem();
+
+      index.set(item, idx);
+
+      laceItem(idx, rdx);
+
+      items[idx].item = item;
+      items[idx].parent = rdx;
+
+      ++classes[~(items[rdx].parent)].size;
+    }
+
+    /// \brief Clears the union-find data structure
+    ///
+    /// Erase each item from the data structure.
+    void clear() {
+      items.clear();
+      firstClass = -1;
+      firstFreeItem = -1;
+    }
+
+    /// \brief Finds the component of the given element.
+    ///
+    /// The method returns the component id of the given element.
+    int find(const Item &item) const {
+      return ~(items[repIndex(index[item])].parent);
+    }
+
+    /// \brief Joining the component of element \e a and element \e b.
+    ///
+    /// This is the \e union operation of the Union-Find structure. 
+    /// Joins the component of element \e a and component of
+    /// element \e b. If \e a and \e b are in the same component then
+    /// returns -1 else returns the remaining class.
+    int join(const Item& a, const Item& b) {
+
+      int ak = repIndex(index[a]);
+      int bk = repIndex(index[b]);
+
+      if (ak == bk) {
+	return -1;
+      }
+
+      int acx = ~(items[ak].parent);
+      int bcx = ~(items[bk].parent);
+
+      int rcx;
+
+      if (classes[acx].size > classes[bcx].size) {
+	classes[acx].size += classes[bcx].size;
+	items[bk].parent = ak;
+        unlaceClass(bcx);
+	rcx = acx;
+      } else {
+	classes[bcx].size += classes[acx].size;
+	items[ak].parent = bk;
+        unlaceClass(acx);
+	rcx = bcx;
+      }
+      spliceItems(ak, bk);
+
+      return rcx;
+    }
+
+    /// \brief Returns the size of the class.
+    ///
+    /// Returns the size of the class.
+    int size(int cls) const {
+      return classes[cls].size;
+    }
+
+    /// \brief Splits up the component. 
+    ///
+    /// Splitting the component into singleton components (component
+    /// of size one).
+    void split(int cls) {
+      int fdx = classes[cls].firstItem;
+      int idx = items[fdx].next;
+      while (idx != fdx) {
+        int next = items[idx].next;
+
+	singletonItem(idx);
+
+	int cdx = newClass();        
+        items[idx].parent = ~cdx;
+
+	laceClass(cdx);
+	classes[cdx].size = 1;
+	classes[cdx].firstItem = idx;
+        
+        idx = next;
+      }
+
+      items[idx].prev = idx;
+      items[idx].next = idx;
+
+      classes[~(items[idx].parent)].size = 1;
+      
+    }
+
+    /// \brief Removes the given element from the structure.
+    ///
+    /// Removes the element from its component and if the component becomes
+    /// empty then removes that component from the component list.
+    ///
+    /// \warning It is an error to remove an element which is not in
+    /// the structure.
+    /// \warning This running time of this operation is proportional to the
+    /// number of the items in this class.
+    void erase(const Item& item) {
+      int idx = index[item];
+      int fdx = items[idx].next;
+
+      int cdx = classIndex(idx);
+      if (idx == fdx) {
+	unlaceClass(cdx);
+	items[idx].next = firstFreeItem;
+	firstFreeItem = idx;
+	return;
+      } else {
+	classes[cdx].firstItem = fdx;
+	--classes[cdx].size;
+	items[fdx].parent = ~cdx;
+
+	unlaceItem(idx);
+	idx = items[fdx].next;
+	while (idx != fdx) {
+	  items[idx].parent = fdx;
+	  idx = items[idx].next;
+	}
+          
+      }
+
+    }
+
+    /// \brief Gives back a representant item of the component.
+    ///
+    /// Gives back a representant item of the component.
+    Item item(int cls) const {
+      return items[classes[cls].firstItem].item;
+    }
+
+    /// \brief Removes the component of the given element from the structure.
+    ///
+    /// Removes the component of the given element from the structure.
+    ///
+    /// \warning It is an error to give an element which is not in the
+    /// structure.
+    void eraseClass(int cls) {
+      int fdx = classes[cls].firstItem;
+      unlaceClass(cls);
+      items[items[fdx].prev].next = firstFreeItem;
+      firstFreeItem = fdx;
+    }
+
+    /// \brief Lemon style iterator for the representant items.
+    ///
+    /// ClassIt is a lemon style iterator for the components. It iterates
+    /// on the ids of the classes.
+    class ClassIt {
+    public:
+      /// \brief Constructor of the iterator
+      ///
+      /// Constructor of the iterator
+      ClassIt(const UnionFindEnum& ufe) : unionFind(&ufe) {
+        cdx = unionFind->firstClass;
+      }
+
+      /// \brief Constructor to get invalid iterator
+      ///
+      /// Constructor to get invalid iterator
+      ClassIt(Invalid) : unionFind(0), cdx(-1) {}
+      
+      /// \brief Increment operator
+      ///
+      /// It steps to the next representant item.
+      ClassIt& operator++() {
+        cdx = unionFind->classes[cdx].next;
+        return *this;
+      }
+      
+      /// \brief Conversion operator
+      ///
+      /// It converts the iterator to the current representant item.
+      operator int() const {
+        return cdx;
+      }
+
+      /// \brief Equality operator
+      ///
+      /// Equality operator
+      bool operator==(const ClassIt& i) { 
+        return i.cdx == cdx;
+      }
+
+      /// \brief Inequality operator
+      ///
+      /// Inequality operator
+      bool operator!=(const ClassIt& i) { 
+        return i.cdx != cdx;
+      }
+      
+    private:
+      const UnionFindEnum* unionFind;
+      int cdx;
+    };
+
+    /// \brief Lemon style iterator for the items of a component.
+    ///
+    /// ClassIt is a lemon style iterator for the components. It iterates
+    /// on the items of a class. By example if you want to iterate on
+    /// each items of each classes then you may write the next code.
+    ///\code
+    /// for (ClassIt cit(ufe); cit != INVALID; ++cit) {
+    ///   std::cout << "Class: ";
+    ///   for (ItemIt iit(ufe, cit); iit != INVALID; ++iit) {
+    ///     std::cout << toString(iit) << ' ' << std::endl;
+    ///   }
+    ///   std::cout << std::endl;
+    /// }
+    ///\endcode
+    class ItemIt {
+    public:
+      /// \brief Constructor of the iterator
+      ///
+      /// Constructor of the iterator. The iterator iterates
+      /// on the class of the \c item.
+      ItemIt(const UnionFindEnum& ufe, int cls) : unionFind(&ufe) {
+        fdx = idx = unionFind->classes[cls].firstItem;
+      }
+
+      /// \brief Constructor to get invalid iterator
+      ///
+      /// Constructor to get invalid iterator
+      ItemIt(Invalid) : unionFind(0), idx(-1) {}
+      
+      /// \brief Increment operator
+      ///
+      /// It steps to the next item in the class.
+      ItemIt& operator++() {
+        idx = unionFind->items[idx].next;
+        if (idx == fdx) idx = -1;
+        return *this;
+      }
+      
+      /// \brief Conversion operator
+      ///
+      /// It converts the iterator to the current item.
+      operator const Item&() const {
+        return unionFind->items[idx].item;
+      }
+
+      /// \brief Equality operator
+      ///
+      /// Equality operator
+      bool operator==(const ItemIt& i) { 
+        return i.idx == idx;
+      }
+
+      /// \brief Inequality operator
+      ///
+      /// Inequality operator
+      bool operator!=(const ItemIt& i) { 
+        return i.idx != idx;
+      }
+      
+    private:
+      const UnionFindEnum* unionFind;
+      int idx, fdx;
+    };
+
+  };
+
+  /// \ingroup auxdat
+  ///
+  /// \brief A \e Extend-Find data structure implementation which
+  /// is able to enumerate the components.
+  ///
+  /// The class implements an \e Extend-Find data structure which is
+  /// able to enumerate the components and the items in a
+  /// component. The data structure is a simplification of the
+  /// Union-Find structure, and it does not allow to merge two components.
+  ///
+  /// \pre You need to add all the elements by the \ref insert()
+  /// method.
+  template <typename _ItemIntMap>
+  class ExtendFindEnum {
+  public:
+    
+    typedef _ItemIntMap ItemIntMap;
+    typedef typename ItemIntMap::Key Item;
+
+  private:
+    
+    ItemIntMap& index;
+
+    struct ItemT {
+      int cls;
+      Item item;
+      int next, prev;
+    };
+
+    std::vector<ItemT> items;
+    int firstFreeItem;
+
+    struct ClassT {
+      int firstItem;
+      int next, prev;
+    };
+
+    std::vector<ClassT> classes;
+
+    int firstClass, firstFreeClass;
+
+    int newClass() {
+      if (firstFreeClass != -1) {
+	int cdx = firstFreeClass;
+	firstFreeClass = classes[cdx].next;
+	return cdx;
+      } else {
+	classes.push_back(ClassT());
+	return classes.size() - 1;
+      }
+    }
+
+    int newItem() {
+      if (firstFreeItem != -1) {
+	int idx = firstFreeItem;
+	firstFreeItem = items[idx].next;
+	return idx;
+      } else {
+	items.push_back(ItemT());
+	return items.size() - 1;
+      }
+    }
+
+  public:
+
+    /// \brief Constructor
+    ExtendFindEnum(ItemIntMap& _index) 
+      : index(_index), items(), firstFreeItem(-1), 
+	classes(), firstClass(-1), firstFreeClass(-1) {}
+    
+    /// \brief Inserts the given element into a new component.
+    ///
+    /// This method creates a new component consisting only of the
+    /// given element.
+    int insert(const Item& item) {
+      int cdx = newClass();
+      classes[cdx].prev = -1;
+      classes[cdx].next = firstClass;
+      if (firstClass != -1) {
+	classes[firstClass].prev = cdx;
+      }
+      firstClass = cdx;
+      
+      int idx = newItem();
+      items[idx].item = item;
+      items[idx].cls = cdx;
+      items[idx].prev = idx;
+      items[idx].next = idx;
+
+      classes[cdx].firstItem = idx;
+
+      index.set(item, idx);
+      
+      return cdx;
+    }
+
+    /// \brief Inserts the given element into the given component.
+    ///
+    /// This methods inserts the element \e item a into the \e cls class.
+    void insert(const Item& item, int cls) {
+      int idx = newItem();
+      int rdx = classes[cls].firstItem;
+      items[idx].item = item;
+      items[idx].cls = cls;
+
+      items[idx].prev = rdx;
+      items[idx].next = items[rdx].next;
+      items[items[rdx].next].prev = idx;
+      items[rdx].next = idx;
+
+      index.set(item, idx);
+    }
+
+    /// \brief Clears the union-find data structure
+    ///
+    /// Erase each item from the data structure.
+    void clear() {
+      items.clear();
+      classes.clear;
+      firstClass = firstFreeClass = firstFreeItem = -1;
+    }
+
+    /// \brief Gives back the class of the \e item.
+    ///
+    /// Gives back the class of the \e item.
+    int find(const Item &item) const {
+      return items[index[item]].cls;
+    }
+
+    /// \brief Gives back a representant item of the component.
+    ///
+    /// Gives back a representant item of the component.
+    Item item(int cls) const {
+      return items[classes[cls].firstItem].item;
+    }
+    
+    /// \brief Removes the given element from the structure.
+    ///
+    /// Removes the element from its component and if the component becomes
+    /// empty then removes that component from the component list.
+    ///
+    /// \warning It is an error to remove an element which is not in
+    /// the structure.
+    void erase(const Item &item) {
+      int idx = index[item];
+      int cdx = items[idx].cls;
+      
+      if (idx == items[idx].next) {
+	if (classes[cdx].prev != -1) {
+	  classes[classes[cdx].prev].next = classes[cdx].next; 
+	} else {
+	  firstClass = classes[cdx].next;
+	}
+	if (classes[cdx].next != -1) {
+	  classes[classes[cdx].next].prev = classes[cdx].prev; 
+	}
+	classes[cdx].next = firstFreeClass;
+	firstFreeClass = cdx;
+      } else {
+	classes[cdx].firstItem = items[idx].next;
+	items[items[idx].next].prev = items[idx].prev;
+	items[items[idx].prev].next = items[idx].next;
+      }
+      items[idx].next = firstFreeItem;
+      firstFreeItem = idx;
+	
+    }    
+
+    
+    /// \brief Removes the component of the given element from the structure.
+    ///
+    /// Removes the component of the given element from the structure.
+    ///
+    /// \warning It is an error to give an element which is not in the
+    /// structure.
+    void eraseClass(int cdx) {
+      int idx = classes[cdx].firstItem;
+      items[items[idx].prev].next = firstFreeItem;
+      firstFreeItem = idx;
+
+      if (classes[cdx].prev != -1) {
+	classes[classes[cdx].prev].next = classes[cdx].next; 
+      } else {
+	firstClass = classes[cdx].next;
+      }
+      if (classes[cdx].next != -1) {
+	classes[classes[cdx].next].prev = classes[cdx].prev; 
+      }
+      classes[cdx].next = firstFreeClass;
+      firstFreeClass = cdx;
+    }
+
+    /// \brief Lemon style iterator for the classes.
+    ///
+    /// ClassIt is a lemon style iterator for the components. It iterates
+    /// on the ids of classes.
+    class ClassIt {
+    public:
+      /// \brief Constructor of the iterator
+      ///
+      /// Constructor of the iterator
+      ClassIt(const ExtendFindEnum& ufe) : extendFind(&ufe) {
+        cdx = extendFind->firstClass;
+      }
+
+      /// \brief Constructor to get invalid iterator
+      ///
+      /// Constructor to get invalid iterator
+      ClassIt(Invalid) : extendFind(0), cdx(-1) {}
+      
+      /// \brief Increment operator
+      ///
+      /// It steps to the next representant item.
+      ClassIt& operator++() {
+        cdx = extendFind->classes[cdx].next;
+        return *this;
+      }
+      
+      /// \brief Conversion operator
+      ///
+      /// It converts the iterator to the current class id.
+      operator int() const {
+        return cdx;
+      }
+
+      /// \brief Equality operator
+      ///
+      /// Equality operator
+      bool operator==(const ClassIt& i) { 
+        return i.cdx == cdx;
+      }
+
+      /// \brief Inequality operator
+      ///
+      /// Inequality operator
+      bool operator!=(const ClassIt& i) { 
+        return i.cdx != cdx;
+      }
+      
+    private:
+      const ExtendFindEnum* extendFind;
+      int cdx;
+    };
+
+    /// \brief Lemon style iterator for the items of a component.
+    ///
+    /// ClassIt is a lemon style iterator for the components. It iterates
+    /// on the items of a class. By example if you want to iterate on
+    /// each items of each classes then you may write the next code.
+    ///\code
+    /// for (ClassIt cit(ufe); cit != INVALID; ++cit) {
+    ///   std::cout << "Class: ";
+    ///   for (ItemIt iit(ufe, cit); iit != INVALID; ++iit) {
+    ///     std::cout << toString(iit) << ' ' << std::endl;
+    ///   }
+    ///   std::cout << std::endl;
+    /// }
+    ///\endcode
+    class ItemIt {
+    public:
+      /// \brief Constructor of the iterator
+      ///
+      /// Constructor of the iterator. The iterator iterates
+      /// on the class of the \c item.
+      ItemIt(const ExtendFindEnum& ufe, int cls) : extendFind(&ufe) {
+        fdx = idx = extendFind->classes[cls].firstItem;
+      }
+
+      /// \brief Constructor to get invalid iterator
+      ///
+      /// Constructor to get invalid iterator
+      ItemIt(Invalid) : extendFind(0), idx(-1) {}
+      
+      /// \brief Increment operator
+      ///
+      /// It steps to the next item in the class.
+      ItemIt& operator++() {
+        idx = extendFind->items[idx].next;
+	if (fdx == idx) idx = -1;
+        return *this;
+      }
+      
+      /// \brief Conversion operator
+      ///
+      /// It converts the iterator to the current item.
+      operator const Item&() const {
+        return extendFind->items[idx].item;
+      }
+
+      /// \brief Equality operator
+      ///
+      /// Equality operator
+      bool operator==(const ItemIt& i) { 
+        return i.idx == idx;
+      }
+
+      /// \brief Inequality operator
+      ///
+      /// Inequality operator
+      bool operator!=(const ItemIt& i) { 
+        return i.idx != idx;
+      }
+      
+    private:
+      const ExtendFindEnum* extendFind;
+      int idx, fdx;
+    };
+
+  };
+
+  /// \ingroup auxdat
+  ///
+  /// \brief A \e Union-Find data structure implementation which
+  /// is able to store a priority for each item and retrieve the minimum of
+  /// each class.
+  ///
+  /// A \e Union-Find data structure implementation which is able to
+  /// store a priority for each item and retrieve the minimum of each
+  /// class. In addition, it supports the joining and splitting the
+  /// components. If you don't need this feature then you makes
+  /// better to use the \ref UnionFind class which is more efficient.
+  ///
+  /// The union-find data strcuture based on a (2, 16)-tree with a
+  /// tournament minimum selection on the internal nodes. The insert
+  /// operation takes O(1), the find, set, decrease and increase takes
+  /// O(log(n)), where n is the number of nodes in the current
+  /// component.  The complexity of join and split is O(log(n)*k),
+  /// where n is the sum of the number of the nodes and k is the
+  /// number of joined components or the number of the components
+  /// after the split.
+  ///
+  /// \pre You need to add all the elements by the \ref insert()
+  /// method.
+  ///
+  template <typename _Value, typename _ItemIntMap, 
+            typename _Comp = std::less<_Value> >
+  class HeapUnionFind {
+  public:
+    
+    typedef _Value Value;
+    typedef typename _ItemIntMap::Key Item;
+
+    typedef _ItemIntMap ItemIntMap;
+
+    typedef _Comp Comp;
+
+  private:
+
+    static const int cmax = 16;
+
+    ItemIntMap& index;
+
+    struct ClassNode {
+      int parent;
+      int depth;
+
+      int left, right;
+      int next, prev;
+    };
+
+    int first_class;
+    int first_free_class;
+    std::vector<ClassNode> classes;
+
+    int newClass() {
+      if (first_free_class < 0) {
+        int id = classes.size();
+        classes.push_back(ClassNode());
+        return id;
+      } else {
+        int id = first_free_class;
+        first_free_class = classes[id].next;
+        return id;
+      }
+    }
+
+    void deleteClass(int id) {
+      classes[id].next = first_free_class;
+      first_free_class = id;
+    }
+
+    struct ItemNode {
+      int parent;
+      Item item;
+      Value prio;
+      int next, prev;
+      int left, right;
+      int size;
+    };
+
+    int first_free_node;
+    std::vector<ItemNode> nodes;
+
+    int newNode() {
+      if (first_free_node < 0) {
+        int id = nodes.size();
+        nodes.push_back(ItemNode());
+        return id;
+      } else {
+        int id = first_free_node;
+        first_free_node = nodes[id].next;
+        return id;
+      }
+    }
+
+    void deleteNode(int id) {
+      nodes[id].next = first_free_node;
+      first_free_node = id;
+    }
+
+    Comp comp;
+
+    int findClass(int id) const {
+      int kd = id;
+      while (kd >= 0) {
+        kd = nodes[kd].parent;
+      }
+      return ~kd;
+    }
+
+    int leftNode(int id) const {
+      int kd = ~(classes[id].parent);
+      for (int i = 0; i < classes[id].depth; ++i) {
+        kd = nodes[kd].left;
+      }
+      return kd;
+    }
+
+    int nextNode(int id) const {
+      int depth = 0;
+      while (id >= 0 && nodes[id].next == -1) {
+        id = nodes[id].parent;
+        ++depth;
+      }
+      if (id < 0) {
+        return -1;
+      }
+      id = nodes[id].next;
+      while (depth--) {
+        id = nodes[id].left;      
+      }
+      return id;
+    }
+
+
+    void setPrio(int id) {
+      int jd = nodes[id].left;
+      nodes[id].prio = nodes[jd].prio;
+      nodes[id].item = nodes[jd].item;
+      jd = nodes[jd].next;
+      while (jd != -1) {
+        if (comp(nodes[jd].prio, nodes[id].prio)) {
+          nodes[id].prio = nodes[jd].prio;
+          nodes[id].item = nodes[jd].item;
+        }
+        jd = nodes[jd].next;
+      }
+    }
+
+    void push(int id, int jd) {
+      nodes[id].size = 1;
+      nodes[id].left = nodes[id].right = jd;
+      nodes[jd].next = nodes[jd].prev = -1;
+      nodes[jd].parent = id;
+    }
+
+    void pushAfter(int id, int jd) {
+      int kd = nodes[id].parent;
+      if (nodes[id].next != -1) {
+        nodes[nodes[id].next].prev = jd;
+        if (kd >= 0) {
+          nodes[kd].size += 1;
+        }
+      } else {
+        if (kd >= 0) {
+          nodes[kd].right = jd;
+          nodes[kd].size += 1;
+        }
+      }
+      nodes[jd].next = nodes[id].next;
+      nodes[jd].prev = id;
+      nodes[id].next = jd;
+      nodes[jd].parent = kd;
+    }
+
+    void pushRight(int id, int jd) {
+      nodes[id].size += 1;
+      nodes[jd].prev = nodes[id].right;
+      nodes[jd].next = -1;
+      nodes[nodes[id].right].next = jd;
+      nodes[id].right = jd;
+      nodes[jd].parent = id;
+    }
+
+    void popRight(int id) {
+      nodes[id].size -= 1;
+      int jd = nodes[id].right;
+      nodes[nodes[jd].prev].next = -1;
+      nodes[id].right = nodes[jd].prev;
+    }
+
+    void splice(int id, int jd) {
+      nodes[id].size += nodes[jd].size;
+      nodes[nodes[id].right].next = nodes[jd].left;
+      nodes[nodes[jd].left].prev = nodes[id].right;
+      int kd = nodes[jd].left;
+      while (kd != -1) {
+        nodes[kd].parent = id;
+        kd = nodes[kd].next;
+      }
+      nodes[id].right = nodes[jd].right;
+    }
+
+    void split(int id, int jd) {
+      int kd = nodes[id].parent;
+      nodes[kd].right = nodes[id].prev;
+      nodes[nodes[id].prev].next = -1;
+      
+      nodes[jd].left = id;
+      nodes[id].prev = -1;
+      int num = 0;
+      while (id != -1) {
+        nodes[id].parent = jd;
+        nodes[jd].right = id;
+        id = nodes[id].next;
+        ++num;
+      }      
+      nodes[kd].size -= num;
+      nodes[jd].size = num;
+    }
+
+    void pushLeft(int id, int jd) {
+      nodes[id].size += 1;
+      nodes[jd].next = nodes[id].left;
+      nodes[jd].prev = -1;
+      nodes[nodes[id].left].prev = jd;
+      nodes[id].left = jd;
+      nodes[jd].parent = id;
+    }
+
+    void popLeft(int id) {
+      nodes[id].size -= 1;
+      int jd = nodes[id].left;
+      nodes[nodes[jd].next].prev = -1;
+      nodes[id].left = nodes[jd].next;
+    }
+
+    void repairLeft(int id) {
+      int jd = ~(classes[id].parent);
+      while (nodes[jd].left != -1) {
+	int kd = nodes[jd].left;
+	if (nodes[jd].size == 1) {
+	  if (nodes[jd].parent < 0) {
+	    classes[id].parent = ~kd;
+	    classes[id].depth -= 1;
+	    nodes[kd].parent = ~id;
+	    deleteNode(jd);
+	    jd = kd;
+	  } else {
+	    int pd = nodes[jd].parent;
+	    if (nodes[nodes[jd].next].size < cmax) {
+	      pushLeft(nodes[jd].next, nodes[jd].left);
+	      if (less(nodes[jd].left, nodes[jd].next)) {
+		nodes[nodes[jd].next].prio = nodes[nodes[jd].left].prio;
+		nodes[nodes[jd].next].item = nodes[nodes[jd].left].item;
+	      } 
+	      popLeft(pd);
+	      deleteNode(jd);
+	      jd = pd;
+	    } else {
+	      int ld = nodes[nodes[jd].next].left;
+	      popLeft(nodes[jd].next);
+	      pushRight(jd, ld);
+	      if (less(ld, nodes[jd].left)) {
+		nodes[jd].item = nodes[ld].item;
+		nodes[jd].prio = nodes[jd].prio;
+	      }
+	      if (nodes[nodes[jd].next].item == nodes[ld].item) {
+		setPrio(nodes[jd].next);
+	      }
+	      jd = nodes[jd].left;
+	    }
+	  }
+	} else {
+	  jd = nodes[jd].left;
+	}
+      }
+    }    
+
+    void repairRight(int id) {
+      int jd = ~(classes[id].parent);
+      while (nodes[jd].right != -1) {
+	int kd = nodes[jd].right;
+	if (nodes[jd].size == 1) {
+	  if (nodes[jd].parent < 0) {
+	    classes[id].parent = ~kd;
+	    classes[id].depth -= 1;
+	    nodes[kd].parent = ~id;
+	    deleteNode(jd);
+	    jd = kd;
+	  } else {
+	    int pd = nodes[jd].parent;
+	    if (nodes[nodes[jd].prev].size < cmax) {
+	      pushRight(nodes[jd].prev, nodes[jd].right);
+	      if (less(nodes[jd].right, nodes[jd].prev)) {
+		nodes[nodes[jd].prev].prio = nodes[nodes[jd].right].prio;
+		nodes[nodes[jd].prev].item = nodes[nodes[jd].right].item;
+	      } 
+	      popRight(pd);
+	      deleteNode(jd);
+	      jd = pd;
+	    } else {
+	      int ld = nodes[nodes[jd].prev].right;
+	      popRight(nodes[jd].prev);
+	      pushLeft(jd, ld);
+	      if (less(ld, nodes[jd].right)) {
+		nodes[jd].item = nodes[ld].item;
+		nodes[jd].prio = nodes[jd].prio;
+	      }
+	      if (nodes[nodes[jd].prev].item == nodes[ld].item) {
+		setPrio(nodes[jd].prev);
+	      }
+	      jd = nodes[jd].right;
+	    }
+	  }
+	} else {
+	  jd = nodes[jd].right;
+	}
+      }
+    }
+
+
+    bool less(int id, int jd) const {
+      return comp(nodes[id].prio, nodes[jd].prio);
+    }
+
+    bool equal(int id, int jd) const {
+      return !less(id, jd) && !less(jd, id);
+    }
+
+
+  public:
+
+    /// \brief Returns true when the given class is alive.
+    ///
+    /// Returns true when the given class is alive, ie. the class is
+    /// not nested into other class.
+    bool alive(int cls) const {
+      return classes[cls].parent < 0;
+    }
+
+    /// \brief Returns true when the given class is trivial.
+    ///
+    /// Returns true when the given class is trivial, ie. the class
+    /// contains just one item directly.
+    bool trivial(int cls) const {
+      return classes[cls].left == -1;
+    }
+
+    /// \brief Constructs the union-find.
+    ///
+    /// Constructs the union-find.  
+    /// \brief _index The index map of the union-find. The data
+    /// structure uses internally for store references.
+    HeapUnionFind(ItemIntMap& _index) 
+      : index(_index), first_class(-1), 
+	first_free_class(-1), first_free_node(-1) {}
+
+    /// \brief Insert a new node into a new component.
+    ///
+    /// Insert a new node into a new component.
+    /// \param item The item of the new node.
+    /// \param prio The priority of the new node.
+    /// \return The class id of the one-item-heap.
+    int insert(const Item& item, const Value& prio) {
+      int id = newNode();
+      nodes[id].item = item;
+      nodes[id].prio = prio;
+      nodes[id].size = 0;
+
+      nodes[id].prev = -1;
+      nodes[id].next = -1;
+
+      nodes[id].left = -1;
+      nodes[id].right = -1;
+
+      nodes[id].item = item;
+      index[item] = id;
+      
+      int class_id = newClass();
+      classes[class_id].parent = ~id;
+      classes[class_id].depth = 0;
+
+      classes[class_id].left = -1;
+      classes[class_id].right = -1;
+      
+      if (first_class != -1) {
+        classes[first_class].prev = class_id;
+      }
+      classes[class_id].next = first_class;
+      classes[class_id].prev = -1;
+      first_class = class_id;
+
+      nodes[id].parent = ~class_id;
+      
+      return class_id;
+    }
+
+    /// \brief The class of the item.
+    ///
+    /// \return The alive class id of the item, which is not nested into
+    /// other classes.
+    ///
+    /// The time complexity is O(log(n)).
+    int find(const Item& item) const {
+      return findClass(index[item]);
+    }
+    
+    /// \brief Joins the classes.
+    ///
+    /// The current function joins the given classes. The parameter is
+    /// an STL range which should be contains valid class ids. The
+    /// time complexity is O(log(n)*k) where n is the overall number
+    /// of the joined nodes and k is the number of classes.
+    /// \return The class of the joined classes.
+    /// \pre The range should contain at least two class ids.
+    template <typename Iterator>
+    int join(Iterator begin, Iterator end) {
+      std::vector<int> cs;
+      for (Iterator it = begin; it != end; ++it) {
+        cs.push_back(*it);
+      }
+
+      int class_id = newClass();
+      { // creation union-find
+
+        if (first_class != -1) {
+          classes[first_class].prev = class_id;
+        }
+        classes[class_id].next = first_class;
+        classes[class_id].prev = -1;
+        first_class = class_id;
+
+        classes[class_id].depth = classes[cs[0]].depth;
+        classes[class_id].parent = classes[cs[0]].parent;
+        nodes[~(classes[class_id].parent)].parent = ~class_id;
+
+        int l = cs[0];
+
+        classes[class_id].left = l;
+        classes[class_id].right = l;
+
+        if (classes[l].next != -1) {
+          classes[classes[l].next].prev = classes[l].prev;
+        }
+        classes[classes[l].prev].next = classes[l].next;
+        
+        classes[l].prev = -1;
+        classes[l].next = -1;
+
+        classes[l].depth = leftNode(l);
+        classes[l].parent = class_id;
+        
+      }
+
+      { // merging of heap
+        int l = class_id;
+        for (int ci = 1; ci < int(cs.size()); ++ci) {
+          int r = cs[ci];
+          int rln = leftNode(r);
+          if (classes[l].depth > classes[r].depth) {
+            int id = ~(classes[l].parent);
+            for (int i = classes[r].depth + 1; i < classes[l].depth; ++i) {
+              id = nodes[id].right;
+            }
+            while (id >= 0 && nodes[id].size == cmax) {
+              int new_id = newNode();
+              int right_id = nodes[id].right;
+
+              popRight(id);
+              if (nodes[id].item == nodes[right_id].item) {
+                setPrio(id);
+              }
+              push(new_id, right_id);
+              pushRight(new_id, ~(classes[r].parent));
+              setPrio(new_id);
+
+              id = nodes[id].parent;
+              classes[r].parent = ~new_id;
+            }
+            if (id < 0) {
+              int new_parent = newNode();
+              nodes[new_parent].next = -1;
+              nodes[new_parent].prev = -1;
+              nodes[new_parent].parent = ~l;
+
+              push(new_parent, ~(classes[l].parent));
+              pushRight(new_parent, ~(classes[r].parent));
+              setPrio(new_parent);
+
+              classes[l].parent = ~new_parent;
+              classes[l].depth += 1;
+            } else {
+              pushRight(id, ~(classes[r].parent));
+              while (id >= 0 && less(~(classes[r].parent), id)) {
+                nodes[id].prio = nodes[~(classes[r].parent)].prio;
+                nodes[id].item = nodes[~(classes[r].parent)].item;
+                id = nodes[id].parent;
+              }
+            }
+          } else if (classes[r].depth > classes[l].depth) {
+            int id = ~(classes[r].parent);
+            for (int i = classes[l].depth + 1; i < classes[r].depth; ++i) {
+              id = nodes[id].left;
+            }
+            while (id >= 0 && nodes[id].size == cmax) {
+              int new_id = newNode();
+              int left_id = nodes[id].left;
+
+              popLeft(id);
+              if (nodes[id].prio == nodes[left_id].prio) {
+                setPrio(id);
+              }
+              push(new_id, left_id);
+              pushLeft(new_id, ~(classes[l].parent));
+              setPrio(new_id);
+
+              id = nodes[id].parent;
+              classes[l].parent = ~new_id;
+
+            }
+            if (id < 0) {
+              int new_parent = newNode();
+              nodes[new_parent].next = -1;
+              nodes[new_parent].prev = -1;
+              nodes[new_parent].parent = ~l;
+
+              push(new_parent, ~(classes[r].parent));
+              pushLeft(new_parent, ~(classes[l].parent));
+              setPrio(new_parent);
+              
+              classes[r].parent = ~new_parent;
+              classes[r].depth += 1;
+            } else {
+              pushLeft(id, ~(classes[l].parent));
+              while (id >= 0 && less(~(classes[l].parent), id)) {
+                nodes[id].prio = nodes[~(classes[l].parent)].prio;
+                nodes[id].item = nodes[~(classes[l].parent)].item;
+                id = nodes[id].parent;
+              }
+            }
+            nodes[~(classes[r].parent)].parent = ~l;
+            classes[l].parent = classes[r].parent;
+            classes[l].depth = classes[r].depth;
+          } else {
+            if (classes[l].depth != 0 && 
+                nodes[~(classes[l].parent)].size + 
+                nodes[~(classes[r].parent)].size <= cmax) {
+              splice(~(classes[l].parent), ~(classes[r].parent));
+              deleteNode(~(classes[r].parent));
+              if (less(~(classes[r].parent), ~(classes[l].parent))) {
+                nodes[~(classes[l].parent)].prio = 
+                  nodes[~(classes[r].parent)].prio;
+                nodes[~(classes[l].parent)].item = 
+                  nodes[~(classes[r].parent)].item;
+              }
+            } else {
+              int new_parent = newNode();
+              nodes[new_parent].next = nodes[new_parent].prev = -1;
+              push(new_parent, ~(classes[l].parent));
+              pushRight(new_parent, ~(classes[r].parent));
+              setPrio(new_parent);
+            
+              classes[l].parent = ~new_parent;
+              classes[l].depth += 1;
+              nodes[new_parent].parent = ~l;
+            }
+          }
+          if (classes[r].next != -1) {
+            classes[classes[r].next].prev = classes[r].prev;
+          }
+          classes[classes[r].prev].next = classes[r].next;
+
+          classes[r].prev = classes[l].right;
+          classes[classes[l].right].next = r;
+          classes[l].right = r;
+          classes[r].parent = l;
+
+          classes[r].next = -1;
+          classes[r].depth = rln;
+        }
+      }
+      return class_id;
+    }
+
+    /// \brief Split the class to subclasses.
+    ///
+    /// The current function splits the given class. The join, which
+    /// made the current class, stored a reference to the
+    /// subclasses. The \c splitClass() member restores the classes
+    /// and creates the heaps. The parameter is an STL output iterator
+    /// which will be filled with the subclass ids. The time
+    /// complexity is O(log(n)*k) where n is the overall number of
+    /// nodes in the splitted classes and k is the number of the
+    /// classes.
+    template <typename Iterator>
+    void split(int cls, Iterator out) {
+      std::vector<int> cs;
+      { // splitting union-find
+        int id = cls;
+        int l = classes[id].left;
+
+        classes[l].parent = classes[id].parent;
+        classes[l].depth = classes[id].depth;
+
+        nodes[~(classes[l].parent)].parent = ~l;
+
+        *out++ = l;
+
+        while (l != -1) {
+          cs.push_back(l);
+          l = classes[l].next;
+        }
+
+        classes[classes[id].right].next = first_class;
+        classes[first_class].prev = classes[id].right;
+        first_class = classes[id].left;
+        
+        if (classes[id].next != -1) {
+          classes[classes[id].next].prev = classes[id].prev;
+        }
+        classes[classes[id].prev].next = classes[id].next;
+        
+        deleteClass(id);
+      }
+
+      {
+        for (int i = 1; i < int(cs.size()); ++i) {
+          int l = classes[cs[i]].depth;
+          while (nodes[nodes[l].parent].left == l) {
+            l = nodes[l].parent;
+          }
+          int r = l;    
+          while (nodes[l].parent >= 0) {
+            l = nodes[l].parent;
+            int new_node = newNode();
+
+            nodes[new_node].prev = -1;
+            nodes[new_node].next = -1;
+
+            split(r, new_node);
+            pushAfter(l, new_node);
+            setPrio(l);
+            setPrio(new_node);
+            r = new_node;
+          }
+          classes[cs[i]].parent = ~r;
+          classes[cs[i]].depth = classes[~(nodes[l].parent)].depth;
+          nodes[r].parent = ~cs[i];
+
+          nodes[l].next = -1;
+          nodes[r].prev = -1;
+
+          repairRight(~(nodes[l].parent));
+          repairLeft(cs[i]);
+          
+          *out++ = cs[i];
+        }
+      }
+    }
+
+    /// \brief Gives back the priority of the current item.
+    ///
+    /// \return Gives back the priority of the current item.
+    const Value& operator[](const Item& item) const {
+      return nodes[index[item]].prio;
+    }
+
+    /// \brief Sets the priority of the current item.
+    ///
+    /// Sets the priority of the current item.
+    void set(const Item& item, const Value& prio) {
+      if (comp(prio, nodes[index[item]].prio)) {
+        decrease(item, prio);
+      } else if (!comp(prio, nodes[index[item]].prio)) {
+        increase(item, prio);
+      }
+    }
+      
+    /// \brief Increase the priority of the current item.
+    ///
+    /// Increase the priority of the current item.
+    void increase(const Item& item, const Value& prio) {
+      int id = index[item];
+      int kd = nodes[id].parent;
+      nodes[id].prio = prio;
+      while (kd >= 0 && nodes[kd].item == item) {
+        setPrio(kd);
+        kd = nodes[kd].parent;
+      }
+    }
+
+    /// \brief Increase the priority of the current item.
+    ///
+    /// Increase the priority of the current item.
+    void decrease(const Item& item, const Value& prio) {
+      int id = index[item];
+      int kd = nodes[id].parent;
+      nodes[id].prio = prio;
+      while (kd >= 0 && less(id, kd)) {
+        nodes[kd].prio = prio;
+        nodes[kd].item = item;
+        kd = nodes[kd].parent;
+      }
+    }
+    
+    /// \brief Gives back the minimum priority of the class.
+    ///
+    /// \return Gives back the minimum priority of the class.
+    const Value& classPrio(int cls) const {
+      return nodes[~(classes[cls].parent)].prio;
+    }
+
+    /// \brief Gives back the minimum priority item of the class.
+    ///
+    /// \return Gives back the minimum priority item of the class.
+    const Item& classTop(int cls) const {
+      return nodes[~(classes[cls].parent)].item;
+    }
+
+    /// \brief Gives back a representant item of the class.
+    /// 
+    /// The representant is indpendent from the priorities of the
+    /// items. 
+    /// \return Gives back a representant item of the class.
+    const Item& classRep(int id) const {
+      int parent = classes[id].parent;
+      return nodes[parent >= 0 ? classes[id].depth : leftNode(id)].item;
+    }
+
+    /// \brief Lemon style iterator for the items of a class.
+    ///
+    /// ClassIt is a lemon style iterator for the components. It iterates
+    /// on the items of a class. By example if you want to iterate on
+    /// each items of each classes then you may write the next code.
+    ///\code
+    /// for (ClassIt cit(huf); cit != INVALID; ++cit) {
+    ///   std::cout << "Class: ";
+    ///   for (ItemIt iit(huf, cit); iit != INVALID; ++iit) {
+    ///     std::cout << toString(iit) << ' ' << std::endl;
+    ///   }
+    ///   std::cout << std::endl;
+    /// }
+    ///\endcode
+    class ItemIt {
+    private:
+
+      const HeapUnionFind* _huf;
+      int _id, _lid;
+      
+    public:
+
+      /// \brief Default constructor 
+      ///
+      /// Default constructor 
+      ItemIt() {}
+
+      ItemIt(const HeapUnionFind& huf, int cls) : _huf(&huf) {
+        int id = cls;
+        int parent = _huf->classes[id].parent;
+        if (parent >= 0) {
+          _id = _huf->classes[id].depth;
+          if (_huf->classes[id].next != -1) {
+            _lid = _huf->classes[_huf->classes[id].next].depth;
+          } else {
+            _lid = -1;
+          }
+        } else {
+          _id = _huf->leftNode(id);
+          _lid = -1;
+        } 
+      }
+      
+      /// \brief Increment operator
+      ///
+      /// It steps to the next item in the class.
+      ItemIt& operator++() {
+        _id = _huf->nextNode(_id);
+        return *this;
+      }
+
+      /// \brief Conversion operator
+      ///
+      /// It converts the iterator to the current item.
+      operator const Item&() const {
+        return _huf->nodes[_id].item;
+      }
+      
+      /// \brief Equality operator
+      ///
+      /// Equality operator
+      bool operator==(const ItemIt& i) { 
+        return i._id == _id;
+      }
+
+      /// \brief Inequality operator
+      ///
+      /// Inequality operator
+      bool operator!=(const ItemIt& i) { 
+        return i._id != _id;
+      }
+
+      /// \brief Equality operator
+      ///
+      /// Equality operator
+      bool operator==(Invalid) { 
+        return _id == _lid;
+      }
+
+      /// \brief Inequality operator
+      ///
+      /// Inequality operator
+      bool operator!=(Invalid) { 
+        return _id != _lid;
+      }
+      
+    };
+
+    /// \brief Class iterator
+    ///
+    /// The iterator stores 
+    class ClassIt {
+    private:
+
+      const HeapUnionFind* _huf;
+      int _id;
+
+    public:
+
+      ClassIt(const HeapUnionFind& huf) 
+        : _huf(&huf), _id(huf.first_class) {}
+
+      ClassIt(const HeapUnionFind& huf, int cls) 
+        : _huf(&huf), _id(huf.classes[cls].left) {}
+
+      ClassIt(Invalid) : _huf(0), _id(-1) {}
+      
+      const ClassIt& operator++() {
+        _id = _huf->classes[_id].next;
+	return *this;
+      }
+
+      /// \brief Equality operator
+      ///
+      /// Equality operator
+      bool operator==(const ClassIt& i) { 
+        return i._id == _id;
+      }
+
+      /// \brief Inequality operator
+      ///
+      /// Inequality operator
+      bool operator!=(const ClassIt& i) { 
+        return i._id != _id;
+      }      
+      
+      operator int() const {
+	return _id;
+      }
+            
+    };
+
+  };
+
+  //! @}
+
+} //namespace lemon
+
+#endif //LEMON_UNION_FIND_H