libstdc++-v3/testsuite/25_algorithms/nth_element/3.cc

   1 // Copyright (C) 2001-2020 Free Software Foundation, Inc.
   2 //
   3 // This file is part of the GNU ISO C++ Library.  This library is free
   4 // software; you can redistribute it and/or modify it under the
   5 // terms of the GNU General Public License as published by the
   6 // Free Software Foundation; either version 3, or (at your option)
   7 // any later version.
   8
   9 // This library is distributed in the hope that it will be useful,
  10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 // GNU General Public License for more details.
  13
  14 // You should have received a copy of the GNU General Public License along
  15 // with this library; see the file COPYING3.  If not see
  16 // <http://www.gnu.org/licenses/>.
  17
  18 // 25.3.1 algorithms, sort()
  19
  20 #include <algorithm>
  21 #include <testsuite_hooks.h>
  22
  23 const int A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20};
  24 const int B[] = {10, 20, 1, 11, 2, 12, 3, 13, 4, 14, 5, 15, 6, 16, 7, 17, 8, 18, 9, 19};
  25 const int C[] = {20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1};
  26 const int N = sizeof(A) / sizeof(int);
  27 const int logN = 3; // ln(N) rounded up
  28 const int P = 7;
  29
  30 // comparison predicate for stable_sort: order by rightmost digit
  31 struct CompLast
  32 {
  33   bool
  34   operator()(const int x, const int y)
  35   { return x % 10 < y % 10; }
  36 };
  37
  38 // This functor has the equivalent functionality of std::geater<>,
  39 // but there is no dependency on <functional> and it also tracks the
  40 // number of invocations since creation.
  41 class Gt
  42 {
  43 public:
  44   static int count() { return itsCount; }
  45   static void reset() { itsCount = 0; }
  46
  47   bool
  48   operator()(const int& x, const int& y)
  49   {
  50     ++itsCount;
  51     return x > y;
  52   }
  53
  54 private:
  55     static int itsCount;
  56 };
  57
  58 int Gt::itsCount = 0;
  59
  60 // 25.3.2 nth_element()
  61 void
  62 test05()
  63 {
  64     using std::nth_element;
  65
  66     int s1[N];
  67     std::copy(B, B + N, s1);
  68     VERIFY(std::equal(s1, s1 + N, B));
  69
  70     int* pn = s1 + (N / 2) - 1;
  71     nth_element(s1, pn, s1 + N);
  72     for (const int* i = pn; i < s1 + N; ++i) VERIFY(!(*i < *pn));
  73
  74     CompLast pred;
  75     nth_element(s1, pn, s1 + N, pred);
  76     for (const int* i = pn; i < s1 + N; ++i) VERIFY(!pred(*i, *pn));
  77 }
  78
  79 int
  80 main()
  81 {
  82   test05();
  83   return 0;
  84 }