libstdc++-v3/testsuite/ext/pb_ds/example/basic_multiset.cc

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2005-2020 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the terms
   7 // of the GNU General Public License as published by the Free Software
   8 // Foundation; either version 3, or (at your option) any later
   9 // version.
  10
  11 // This library is distributed in the hope that it will be useful, but
  12 // WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 // General Public License for more details.
  15
  16 // You should have received a copy of the GNU General Public License
  17 // along with this library; see the file COPYING3.  If not see
  18 // <http://www.gnu.org/licenses/>.
  19
  20
  21 // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
  22
  23 // Permission to use, copy, modify, sell, and distribute this software
  24 // is hereby granted without fee, provided that the above copyright
  25 // notice appears in all copies, and that both that copyright notice
  26 // and this permission notice appear in supporting documentation. None
  27 // of the above authors, nor IBM Haifa Research Laboratories, make any
  28 // representation about the suitability of this software for any
  29 // purpose. It is provided "as is" without express or implied
  30 // warranty.
  31
  32 /**
  33  * @file basic_multiset_example.cpp
  34  * A basic example showing how to use multisets.
  35  */
  36
  37
  38 // This example shows how to use "multisets".
  39
  40 // In this example we build a very simple priority queue that also can
  41 // be queried if an entry contains (i.e., it is slightly similar to an
  42 // associative container as well as a priority queue). The priority
  43 // queue adapts a "multiset".
  44
  45 // (Note that there are more efficient ways for implementing this than
  46 // by adapting an associative container. This is just an example for
  47 // "multisets".)
  48
  49 #include <iostream>
  50 #include <cassert>
  51 #include <ext/pb_ds/assoc_container.hpp>
  52
  53 using namespace std;
  54 using namespace __gnu_pbds;
  55
  56 // A simple priority queue that also supports an "contains" query.
  57 class contains_pq
  58 {
  59 public:
  60   // Pushes an integer.
  61   void
  62   push(int i);
  63
  64   // Pops the largest integer and returns it.
  65   int
  66   pop();
  67
  68   // Returns true iff i is contained in the container.
  69   bool
  70   contains(int i) const
  71   { return m_tree.find(i) != m_tree.end(); }
  72
  73   // Returns true iff empty.
  74   bool
  75   empty() const
  76   { return m_tree.empty(); }
  77
  78 private:
  79   // This is the container type we adapt - a "multiset".
  80   // It maps each integer to the number of times it logically appears.
  81   typedef
  82   tree<
  83   int,
  84   size_t,
  85   greater<
  86   int> >
  87   tree_t;
  88
  89 private:
  90   tree_t m_tree;
  91 };
  92
  93 void
  94 contains_pq::
  95 push(int i)
  96 {
  97   // To push i, we insert to the "multiset" that i appears 0 times
  98   // (which is a no-op if i already is contained), then increment the
  99   // number of times i is contained by 1.
 100   ++m_tree.insert(make_pair(i, 0)).first->second;
 101 }
 102
 103 int
 104 contains_pq::
 105 pop()
 106 {
 107   assert(!empty());
 108
 109   // The element we need to pop must be the first one, since tree_t is
 110   // an ordered container.
 111   tree_t::iterator it = m_tree.begin();
 112
 113   const int i = it->first;
 114
 115   // Decrease the number of times the popped element appears in the
 116   // container object. If it is 0 - we erase it.
 117   if (--it->second == 0)
 118     m_tree.erase(it);
 119
 120   return i;
 121 }
 122
 123 int main()
 124 {
 125   contains_pq cpq;
 126
 127   // First we push some elements.
 128   cpq.push(4);
 129   cpq.push(3);
 130   cpq.push(2);
 131   cpq.push(1);
 132   cpq.push(4);
 133
 134   // Note that logically, 4 appears 2 times, and each of 1, 2, and 3
 135   // appear once.
 136   assert(cpq.contains(4));
 137   assert(cpq.contains(3));
 138   assert(cpq.contains(2));
 139   assert(cpq.contains(1));
 140
 141   // Now pop the topmost element - it should be 4.
 142   assert(cpq.pop() == 4);
 143
 144   // Now logically, each of 1, 2, 3, and 4 appear once.
 145   assert(cpq.contains(4));
 146
 147   // We pop the topmost element - it should be 4.
 148   assert(cpq.pop() == 4);
 149
 150   // 4 should not be contained any more.
 151   assert(!cpq.contains(4));
 152
 153   assert(cpq.contains(3));
 154   assert(cpq.contains(2));
 155   assert(cpq.contains(1));
 156
 157   assert(cpq.pop() == 3);
 158   assert(cpq.pop() == 2);
 159   assert(cpq.pop() == 1);
 160
 161   assert(cpq.empty());
 162
 163   return 0;
 164 }
 165