// -*- 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; }