// -*- C++ -*-
// Copyright (C) 2005, 2006, 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
// .
// 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 basic_multiset_example.cpp
* A basic example showing how to use multisets.
*/
// This example shows how to use "multisets".
// In this example we build a very simple priority queue that also can
// be queried if an entry contains (i.e., it is slightly similar to an
// associative container as well as a priority queue). The priority
// queue adapts a "multiset".
// (Note that there are more efficient ways for implementing this than
// by adapting an associative container. This is just an example for
// "multisets".)
#include
#include
#include
using namespace std;
using namespace __gnu_pbds;
// A simple priority queue that also supports an "contains" query.
class contains_pq
{
public:
// Pushes an integer.
void
push(int i);
// Pops the largest integer and returns it.
int
pop();
// Returns true iff i is contained in the container.
bool
contains(int i) const
{ return m_tree.find(i) != m_tree.end(); }
// Returns true iff empty.
bool
empty() const
{ return m_tree.empty(); }
private:
// This is the container type we adapt - a "multiset".
// It maps each integer to the number of times it logically appears.
typedef
tree<
int,
size_t,
greater<
int> >
tree_t;
private:
tree_t m_tree;
};
void
contains_pq::
push(int i)
{
// To push i, we insert to the "multiset" that i appears 0 times
// (which is a no-op if i already is contained), then increment the
// number of times i is contained by 1.
++m_tree.insert(make_pair(i, 0)).first->second;
}
int
contains_pq::
pop()
{
assert(!empty());
// The element we need to pop must be the first one, since tree_t is
// an ordered container.
tree_t::iterator it = m_tree.begin();
const int i = it->first;
// Decrease the number of times the popped element appears in the
// container object. If it is 0 - we erase it.
if (--it->second == 0)
m_tree.erase(it);
return i;
}
int main()
{
contains_pq cpq;
// First we push some elements.
cpq.push(4);
cpq.push(3);
cpq.push(2);
cpq.push(1);
cpq.push(4);
// Note that logically, 4 appears 2 times, and each of 1, 2, and 3
// appear once.
assert(cpq.contains(4));
assert(cpq.contains(3));
assert(cpq.contains(2));
assert(cpq.contains(1));
// Now pop the topmost element - it should be 4.
assert(cpq.pop() == 4);
// Now logically, each of 1, 2, 3, and 4 appear once.
assert(cpq.contains(4));
// We pop the topmost element - it should be 4.
assert(cpq.pop() == 4);
// 4 should not be contained any more.
assert(!cpq.contains(4));
assert(cpq.contains(3));
assert(cpq.contains(2));
assert(cpq.contains(1));
assert(cpq.pop() == 3);
assert(cpq.pop() == 2);
assert(cpq.pop() == 1);
assert(cpq.empty());
return 0;
}