| // -*- C++ -*- |
| |
| // Copyright (C) 2005, 2006 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 2, 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 COPYING. If not, write to |
| // the Free Software Foundation, 59 Temple Place - Suite 330, Boston, |
| // MA 02111-1307, USA. |
| |
| // As a special exception, you may use this file as part of a free |
| // software library without restriction. Specifically, if other files |
| // instantiate templates or use macros or inline functions from this |
| // file, or you compile this file and link it with other files to |
| // produce an executable, this file does not by itself cause the |
| // resulting executable to be covered by the GNU General Public |
| // License. This exception does not however invalidate any other |
| // reasons why the executable file might be covered by the GNU General |
| // Public License. |
| |
| // 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 <iostream> |
| #include <cassert> |
| #include <ext/pb_ds/assoc_container.hpp> |
| |
| using namespace std; |
| using namespace pb_ds; |
| |
| // 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; |
| } |
| |