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

   1 // Copyright (C) 2020-2025 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 // { dg-do run { target c++20 } }
  19 // { dg-require-cstdint "" }
  20
  21 #include <algorithm>
  22 #include <random>
  23 #include <testsuite_hooks.h>
  24 #include <testsuite_iterators.h>
  25
  26 using __gnu_test::test_container;
  27 using __gnu_test::test_range;
  28 using __gnu_test::random_access_iterator_wrapper;
  29
  30 namespace ranges = std::ranges;
  31
  32 void
  33 test01()
  34 {
  35   int x[50];
  36   std::iota(x, x+50, 0);
  37
  38   auto pred = std::greater{};
  39   auto proj = [] (int a) { return -a; };
  40   for (int i = 0; i < 50; i++)
  41     {
  42       test_range<int, random_access_iterator_wrapper> rx(x);
  43       std::ranlux48_base g(i);
  44       ranges::shuffle(rx, g);
  45
  46       auto result = ranges::nth_element(rx, rx.begin()+i, pred, proj);
  47       VERIFY( result == rx.end() );
  48       VERIFY( x[i] == i );
  49       for (int j = 0; j < i; j++)
  50         for (int k = i; k < 50; k++)
  51           VERIFY( !pred(proj(x[k]), proj(x[j])) );
  52
  53       result = ranges::nth_element(rx, rx.begin()+i, pred);
  54       VERIFY( result == rx.end() );
  55       VERIFY( x[i] == 49-i );
  56       for (int j = 0; j < i; j++)
  57         for (int k = i; k < 50; k++)
  58           VERIFY( !pred(x[k], x[j]) );
  59     }
  60 }
  61
  62 constexpr bool
  63 test02()
  64 {
  65   int x[] = {5,2,1,3,4};
  66   ranges::nth_element(x, x+3);
  67   return x[3] == 4;
  68 }
  69
  70 int
  71 main()
  72 {
  73   test01();
  74   static_assert(test02());
  75 }