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

  *

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

  *

  * Copyright (C) 2003-2009

  * 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_BIN_HEAP_H

 #define LEMON_BIN_HEAP_H

 ///\ingroup auxdat

 ///\file

 ///\brief Binary Heap implementation.

 #include <vector>

 #include <utility>

 #include <functional>

 namespace lemon {

   ///\ingroup auxdat

   ///

   ///\brief A Binary Heap implementation.

   ///

   ///This class implements the \e binary \e heap data structure. 

   /// 

   ///A \e heap is a data structure for storing items with specified values

   ///called \e priorities in such a way that finding the item with minimum

   ///priority is efficient. \c Comp specifies the ordering of the priorities.

   ///In a heap one can change the priority of an item, add or erase an

   ///item, etc.

   ///

   ///\tparam PR Type of the priority of the items.

   ///\tparam IM A read and writable item map with int values, used internally

   ///to handle the cross references.

   ///\tparam Comp A functor class for the ordering of the priorities.

   ///The default is \c std::less<PR>.

   ///

   ///\sa FibHeap

   ///\sa Dijkstra

   template <typename PR, typename IM, typename Comp = std::less<PR> >

   class BinHeap {

   public:

     ///\e

     typedef IM ItemIntMap;

     ///\e

     typedef PR Prio;

     ///\e

     typedef typename ItemIntMap::Key Item;

     ///\e

     typedef std::pair<Item,Prio> Pair;

     ///\e

     typedef Comp Compare;

     /// \brief Type to represent the items states.

     ///

     /// Each Item element have a state associated to it. It may be "in heap",

     /// "pre heap" or "post heap". The latter two are indifferent from the

     /// heap's point of view, but may be useful to the user.

     ///

     /// The item-int map must be initialized in such way that it assigns

     /// \c PRE_HEAP (<tt>-1</tt>) to any element to be put in the heap.

     enum State {

       IN_HEAP = 0,    ///< = 0.

       PRE_HEAP = -1,  ///< = -1.

       POST_HEAP = -2  ///< = -2.

     };

   private:

     std::vector<Pair> _data;

     Compare _comp;

     ItemIntMap &_iim;

   public:

     /// \brief The constructor.

     ///

     /// The constructor.

     /// \param map should be given to the constructor, since it is used

     /// internally to handle the cross references. The value of the map

     /// must be \c PRE_HEAP (<tt>-1</tt>) for every item.

     explicit BinHeap(ItemIntMap &map) : _iim(map) {}

     /// \brief The constructor.

     ///

     /// The constructor.

     /// \param map should be given to the constructor, since it is used

     /// internally to handle the cross references. The value of the map

     /// should be PRE_HEAP (-1) for each element.

     ///

     /// \param comp The comparator function object.

     BinHeap(ItemIntMap &map, const Compare &comp)

       : _iim(map), _comp(comp) {}

     /// The number of items stored in the heap.

     ///

     /// \brief Returns the number of items stored in the heap.

     int size() const { return _data.size(); }

     /// \brief Checks if the heap stores no items.

     ///

     /// Returns \c true if and only if the heap stores no items.

     bool empty() const { return _data.empty(); }

     /// \brief Make empty this heap.

     ///

     /// Make empty this heap. It does not change the cross reference map.

     /// If you want to reuse what is not surely empty you should first clear

     /// the heap and after that you should set the cross reference map for

     /// each item to \c PRE_HEAP.

     void clear() {

       _data.clear();

     }

   private:

     static int parent(int i) { return (i-1)/2; }

     static int second_child(int i) { return 2*i+2; }

     bool less(const Pair &p1, const Pair &p2) const {

       return _comp(p1.second, p2.second);

     }

     int bubble_up(int hole, Pair p) {

       int par = parent(hole);

       while( hole>0 && less(p,_data[par]) ) {

         move(_data[par],hole);

         hole = par;

         par = parent(hole);

       }

       move(p, hole);

       return hole;

     }

     int bubble_down(int hole, Pair p, int length) {

       int child = second_child(hole);

       while(child < length) {

         if( less(_data[child-1], _data[child]) ) {

           --child;

         }

         if( !less(_data[child], p) )

           goto ok;

         move(_data[child], hole);

         hole = child;

         child = second_child(hole);

       }

       child--;

       if( child<length && less(_data[child], p) ) {

         move(_data[child], hole);

         hole=child;

       }

     ok:

       move(p, hole);

       return hole;

     }

     void move(const Pair &p, int i) {

       _data[i] = p;

       _iim.set(p.first, i);

     }

   public:

     /// \brief Insert a pair of item and priority into the heap.

     ///

     /// Adds \c p.first to the heap with priority \c p.second.

     /// \param p The pair to insert.

     void push(const Pair &p) {

       int n = _data.size();

       _data.resize(n+1);

       bubble_up(n, p);

     }

     /// \brief Insert an item into the heap with the given heap.

     ///

     /// Adds \c i to the heap with priority \c p.

     /// \param i The item to insert.

     /// \param p The priority of the item.

     void push(const Item &i, const Prio &p) { push(Pair(i,p)); }

     /// \brief Returns the item with minimum priority relative to \c Compare.

     ///

     /// This method returns the item with minimum priority relative to \c

     /// Compare.

     /// \pre The heap must be nonempty.

     Item top() const {

       return _data[0].first;

     }

     /// \brief Returns the minimum priority relative to \c Compare.

     ///

     /// It returns the minimum priority relative to \c Compare.

     /// \pre The heap must be nonempty.

     Prio prio() const {

       return _data[0].second;

     }

     /// \brief Deletes the item with minimum priority relative to \c Compare.

     ///

     /// This method deletes the item with minimum priority relative to \c

     /// Compare from the heap.

     /// \pre The heap must be non-empty.

     void pop() {

       int n = _data.size()-1;

       _iim.set(_data[0].first, POST_HEAP);

       if (n > 0) {

         bubble_down(0, _data[n], n);

       }

       _data.pop_back();

     }

     /// \brief Deletes \c i from the heap.

     ///

     /// This method deletes item \c i from the heap.

     /// \param i The item to erase.

     /// \pre The item should be in the heap.

     void erase(const Item &i) {

       int h = _iim[i];

       int n = _data.size()-1;

       _iim.set(_data[h].first, POST_HEAP);

       if( h < n ) {

         if ( bubble_up(h, _data[n]) == h) {

           bubble_down(h, _data[n], n);

         }

       }

       _data.pop_back();

     }

     /// \brief Returns the priority of \c i.

     ///

     /// This function returns the priority of item \c i.

     /// \param i The item.

     /// \pre \c i must be in the heap.

     Prio operator[](const Item &i) const {

       int idx = _iim[i];

       return _data[idx].second;

     }

     /// \brief \c i gets to the heap with priority \c p independently

     /// if \c i was already there.

     ///

     /// This method calls \ref push(\c i, \c p) if \c i is not stored

     /// in the heap and sets the priority of \c i to \c p otherwise.

     /// \param i The item.

     /// \param p The priority.

     void set(const Item &i, const Prio &p) {

       int idx = _iim[i];

       if( idx < 0 ) {

         push(i,p);

       }

       else if( _comp(p, _data[idx].second) ) {

         bubble_up(idx, Pair(i,p));

       }

       else {

         bubble_down(idx, Pair(i,p), _data.size());

       }

     }

     /// \brief Decreases the priority of \c i to \c p.

     ///

     /// This method decreases the priority of item \c i to \c p.

     /// \param i The item.

     /// \param p The priority.

     /// \pre \c i must be stored in the heap with priority at least \c

     /// p relative to \c Compare.

     void decrease(const Item &i, const Prio &p) {

       int idx = _iim[i];

       bubble_up(idx, Pair(i,p));

     }

     /// \brief Increases the priority of \c i to \c p.

     ///

     /// This method sets the priority of item \c i to \c p.

     /// \param i The item.

     /// \param p The priority.

     /// \pre \c i must be stored in the heap with priority at most \c

     /// p relative to \c Compare.

     void increase(const Item &i, const Prio &p) {

       int idx = _iim[i];

       bubble_down(idx, Pair(i,p), _data.size());

     }

     /// \brief Returns if \c item is in, has already been in, or has

     /// never been in the heap.

     ///

     /// This method returns PRE_HEAP if \c item has never been in the

     /// heap, IN_HEAP if it is in the heap at the moment, and POST_HEAP

     /// otherwise. In the latter case it is possible that \c item will

     /// get back to the heap again.

     /// \param i The item.

     State state(const Item &i) const {

       int s = _iim[i];

       if( s>=0 )

         s=0;

       return State(s);

     }

     /// \brief Sets the state of the \c item in the heap.

     ///

     /// Sets the state of the \c item in the heap. It can be used to

     /// manually clear the heap when it is important to achive the

     /// better time complexity.

     /// \param i The item.

     /// \param st The state. It should not be \c IN_HEAP.

     void state(const Item& i, State st) {

       switch (st) {

       case POST_HEAP:

       case PRE_HEAP:

         if (state(i) == IN_HEAP) {

           erase(i);

         }

         _iim[i] = st;

         break;

       case IN_HEAP:

         break;

       }

     }

     /// \brief Replaces an item in the heap.

     ///

     /// The \c i item is replaced with \c j item. The \c i item should

     /// be in the heap, while the \c j should be out of the heap. The

     /// \c i item will out of the heap and \c j will be in the heap

     /// with the same prioriority as prevoiusly the \c i item.

     void replace(const Item& i, const Item& j) {

       int idx = _iim[i];

       _iim.set(i, _iim[j]);

       _iim.set(j, idx);

       _data[idx].first = j;

     }

   }; // class BinHeap

 } // namespace lemon

 #endif // LEMON_BIN_HEAP_H