priority_queue.h

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// rak - Rakshasa's toolbox
// Copyright (C) 2005-2006, Jari Sundell
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
// 
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
// 
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//
// In addition, as a special exception, the copyright holders give
// permission to link the code of portions of this program with the
// OpenSSL library under certain conditions as described in each
// individual source file, and distribute linked combinations
// including the two.
//
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// Contact:  Jari Sundell <[e-mail]>
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// priority_queue is a priority queue implemented using a binary
// heap. It can contain multiple instances of a value.

#ifndef RAK_PRIORITY_QUEUE_H
#define RAK_PRIORITY_QUEUE_H

#include <algorithm>
#include <functional>
#include <vector>

namespace rak {

template <typename Value, typename Compare, typename Equal>
class priority_queue : public std::vector<Value> {
public:
  typedef std::vector<Value>                  base_type;
  typedef typename base_type::reference       reference;
  typedef typename base_type::const_reference const_reference;
  typedef typename base_type::iterator        iterator;
  typedef typename base_type::const_iterator  const_iterator;
  typedef typename base_type::value_type      value_type;

  using base_type::begin;
  using base_type::end;
  using base_type::size;
  using base_type::empty;

  priority_queue(Compare l = Compare(), Equal e = Equal())
    : m_compare(l), m_equal(e) {}

  const_reference top() const {
    return base_type::front();
  }

  void pop() {
    std::pop_heap(begin(), end(), m_compare);
    base_type::pop_back();
  }

  void push(const value_type& value) {
    base_type::push_back(value);
    std::push_heap(begin(), end(), m_compare);
  }

  template <typename Key>
  iterator find(const Key& key) {
    return std::find_if(begin(), end(), std::bind2nd(m_equal, key));
  }

  template <typename Key>
  bool erase(const Key& key) {
    iterator itr = find(key);

    if (itr == end())
      return false;

    erase(itr);
    return true;
  }

  // Removes 'itr' from the queue. This assumes 'itr' has been
  // modified such that it has a higher priority than any other
  // element in the queue.
  void erase(iterator itr) {
//     std::push_heap(begin(), ++itr, m_compare);
//     pop();
    base_type::erase(itr);
    std::make_heap(begin(), end(), m_compare);
  }

private:
  Compare             m_compare;
  Equal               m_equal;
};

// Iterate while the top node has higher priority, as 'Compare'
// returns false.
template <typename Queue, typename Compare>
class queue_pop_iterator
  : public std::iterator<std::forward_iterator_tag, void, void, void, void> {
public:
  typedef Queue container_type;

  queue_pop_iterator() : m_queue(NULL) {}
  queue_pop_iterator(Queue* q, Compare c) : m_queue(q), m_compare(c) {}

  queue_pop_iterator& operator ++ ()                     { m_queue->pop(); return *this; }
  queue_pop_iterator& operator ++ (int)                  { m_queue->pop(); return *this; }

  typename container_type::const_reference operator * () { return m_queue->top(); }

  bool operator != (const queue_pop_iterator& itr)       { return !m_queue->empty() && !m_compare(m_queue->top()); }
  bool operator == (const queue_pop_iterator& itr)       { return m_queue->empty() || m_compare(m_queue->top()); }

private:
  Queue*  m_queue;
  Compare m_compare;
};

template <typename Queue, typename Compare>
inline queue_pop_iterator<Queue, Compare>
queue_popper(Queue& queue, Compare comp) {
  return queue_pop_iterator<Queue, Compare>(&queue, comp);
}

}

#endif