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

   1 // Copyright (C) 2020-2022 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-options "-std=gnu++2a" }
  19 // { dg-do run { target c++2a } }
  20 // { dg-require-cstdint "" }
  21
  22 #include <algorithm>
  23 #include <random>
  24 #include <testsuite_hooks.h>
  25 #include <testsuite_iterators.h>
  26
  27 using __gnu_test::test_container;
  28 using __gnu_test::test_range;
  29 using __gnu_test::random_access_iterator_wrapper;
  30
  31 namespace ranges = std::ranges;
  32
  33 void
  34 test01()
  35 {
  36   int x[50];
  37   std::iota(x, x+50, 0);
  38
  39   auto pred = std::greater{};
  40   auto proj = [] (int a) { return -a; };
  41   for (int i = 0; i < 50; i++)
  42     {
  43       test_range<int, random_access_iterator_wrapper> rx(x);
  44       std::ranlux48_base g(i);
  45       ranges::shuffle(rx, g);
  46
  47       auto result = ranges::nth_element(rx, rx.begin()+i, pred, proj);
  48       VERIFY( result == rx.end() );
  49       VERIFY( x[i] == i );
  50       for (int j = 0; j < i; j++)
  51         for (int k = i; k < 50; k++)
  52           VERIFY( !pred(proj(x[k]), proj(x[j])) );
  53
  54       result = ranges::nth_element(rx, rx.begin()+i, pred);
  55       VERIFY( result == rx.end() );
  56       VERIFY( x[i] == 49-i );
  57       for (int j = 0; j < i; j++)
  58         for (int k = i; k < 50; k++)
  59           VERIFY( !pred(x[k], x[j]) );
  60     }
  61 }
  62
  63 constexpr bool
  64 test02()
  65 {
  66   int x[] = {5,2,1,3,4};
  67   ranges::nth_element(x, x+3);
  68   return x[3] == 4;
  69 }
  70
  71 int
  72 main()
  73 {
  74   test01();
  75   static_assert(test02());
  76 }