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// -*- C++ -*-

// Copyright (C) 2005, 2006, 2007, 2009 Free Software Foundation, Inc.

//

// This file is part of the GNU ISO C++ Library.  This library 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 3, or (at your option) any later

// version.

// This library 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 library; see the file COPYING3.  If not see

// <http://www.gnu.org/licenses/>.

// Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.

// Permission to use, copy, modify, sell, and distribute this software

// is hereby granted without fee, provided that the above copyright

// notice appears in all copies, and that both that copyright notice

// and this permission notice appear in supporting documentation. None

// of the above authors, nor IBM Haifa Research Laboratories, make any

// representation about the suitability of this software for any

// purpose. It is provided "as is" without express or implied

// warranty.

/**

 * @file priority_queue_xref_example.cpp

 * A basic example showing how to cross-reference priority queues and other

 *    containers for erase.

 */

/**

 * This example shows how to cross-reference priority queues

 * and other containers. I.e., using an associative container to

 * map keys to entries in a priority queue, and using the priority

 * queue to map entries to the associative container. The combination

 * can be used for fast operations involving both priorities and

 * arbitrary keys.

 *

 * The most useful examples of this technique are usually from the

 * field of graph algorithms (where erasing or modifying an arbitrary

 * entry of a priority queue is sometimes necessary), but a full-blown

 * example would be too long. Instead, this example shows a very simple

 * version of Dijkstra's

 */

#include <iostream>

#include <cassert>

#include <ext/pb_ds/priority_queue.hpp>

#include <ext/pb_ds/assoc_container.hpp>

using namespace std;

using namespace __gnu_pbds;

// A priority queue of integers, which supports fast pushes,

// duplicated-int avoidance, and arbitrary-int erases.

class mapped_priority_queue

{

public:

  // Pushes an int into the container. If the key is already in, this

  // is a no-op.

  void

  push(const int& r_str);

  // Returns a const reference to the largest int in the container.

  int

  top() const

  {

    assert(!empty());

    return m_pq.top();

  }

  // Erases the largest int in the container.

  void

  pop();

  // Erases an arbitrary int. If the int is not in the container, this

  // is a no-op, and the return value is false.

  bool

  erase(const int& r_str);

  bool

  empty() const

  { return m_pq.empty(); }

  size_t

  size() const

  { return m_pq.size(); }

private:

  // A priority queue of strings.

  typedef __gnu_pbds::priority_queue< int> pq_t;

  // A hash-table mapping strings to point_iterators inside the

  // priority queue.

  typedef cc_hash_table< int, pq_t::point_iterator> map_t;

  pq_t m_pq;

  map_t m_map;

};

void

mapped_priority_queue::

push(const int& r_str)

{

  // First check if the int is already in the container. If so, just return.

  if (m_map.find(r_str) != m_map.end())

    return;

  // Push the int into the priority queue, and store a point_iterator to it.

  pq_t::point_iterator pq_it = m_pq.push(r_str);

  try

    {

      // Now make the map associate the int to the point_iterator.

      m_map[r_str] = pq_it;

    }

  catch(...)

    {

      // If the above failed, we need to remove the int from the

      // priority queue as well.

      m_pq.erase(pq_it);

      throw;

    }

}

void

mapped_priority_queue::

pop()

{

  assert(!empty());

  // Erase the int from the map.

  m_map.erase(m_pq.top());

  // ...then from the priority queue.

  m_pq.pop();

}

bool

mapped_priority_queue::

erase(const int& r_str)

{

  map_t::point_iterator map_it = m_map.find(r_str);

  // If the int is not in the map, this is a no-op.

  if (map_it == m_map.end())

    return false;

  // Otherwise, we erase it from the priority queue.

  m_pq.erase(map_it->second);

  // ...then from the map.

  m_map.erase(r_str);

  return true;

}

int main()

{

  // Push some values into the container object.

  mapped_priority_queue m;

  m.push(1);

  m.push(2);

  // The following four operations are no-ops: 2 and 1 are already in

  // the container.

  m.push(2);

  m.push(2);

  m.push(2);

  m.push(1);

  m.push(10);

  m.push(11);

  m.push(12);

  // The size should be 5, since m contains the set {1, 2, 10, 11, 12}.

  assert(m.size() == 5);

  // The largest value should be 12.

  assert(m.top() == 12);

  // Now erase some values.

  // Erasing 1 actually erases a value.

  assert(m.erase(1));

  // ...but erasing 1 again is a no-op.

  assert(!m.erase(1));

  // The size should be 5, since m contains the set {2, 10, 11, 12}.

  assert(m.size() == 4);

  // Now print the values in the container.

  while (!m.empty())

    {

      cout << m.top() << endl;

      m.pop();

    }

  return 0;

}