/* -*- 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,    ///< \e

      PRE_HEAP = -1,  ///< \e

      POST_HEAP = -2  ///< \e

    };

  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