1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef _LIBCPP___ALGORITHM_PARTIAL_SORT_H
10 #define _LIBCPP___ALGORITHM_PARTIAL_SORT_H
11 
12 #include <__algorithm/comp.h>
13 #include <__algorithm/comp_ref_type.h>
14 #include <__algorithm/iterator_operations.h>
15 #include <__algorithm/make_heap.h>
16 #include <__algorithm/sift_down.h>
17 #include <__algorithm/sort_heap.h>
18 #include <__config>
19 #include <__debug>
20 #include <__debug_utils/randomize_range.h>
21 #include <__iterator/iterator_traits.h>
22 #include <__utility/move.h>
23 #include <type_traits>
24 
25 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
26 #  pragma GCC system_header
27 #endif
28 
29 _LIBCPP_BEGIN_NAMESPACE_STD
30 
31 template <class _AlgPolicy, class _Compare, class _RandomAccessIterator, class _Sentinel>
32 _LIBCPP_CONSTEXPR_AFTER_CXX17
33 _RandomAccessIterator __partial_sort_impl(
34     _RandomAccessIterator __first, _RandomAccessIterator __middle, _Sentinel __last, _Compare&& __comp) {
35   if (__first == __middle) {
36     return _IterOps<_AlgPolicy>::next(__middle, __last);
37   }
38 
39   std::__make_heap<_AlgPolicy>(__first, __middle, __comp);
40 
41   typename iterator_traits<_RandomAccessIterator>::difference_type __len = __middle - __first;
42   _RandomAccessIterator __i = __middle;
43   for (; __i != __last; ++__i)
44   {
45       if (__comp(*__i, *__first))
46       {
47           _IterOps<_AlgPolicy>::iter_swap(__i, __first);
48           std::__sift_down<_AlgPolicy>(__first, __comp, __len, __first);
49       }
50 
51   }
52   std::__sort_heap<_AlgPolicy>(std::move(__first), std::move(__middle), __comp);
53 
54   return __i;
55 }
56 
57 template <class _AlgPolicy, class _Compare, class _RandomAccessIterator, class _Sentinel>
58 _LIBCPP_CONSTEXPR_AFTER_CXX17
59 _RandomAccessIterator __partial_sort(_RandomAccessIterator __first, _RandomAccessIterator __middle, _Sentinel __last,
60                                      _Compare& __comp) {
61   if (__first == __middle)
62       return _IterOps<_AlgPolicy>::next(__middle, __last);
63 
64   std::__debug_randomize_range<_AlgPolicy>(__first, __last);
65 
66   using _Comp_ref = typename __comp_ref_type<_Compare>::type;
67   auto __last_iter = std::__partial_sort_impl<_AlgPolicy>(__first, __middle, __last, static_cast<_Comp_ref>(__comp));
68 
69   std::__debug_randomize_range<_AlgPolicy>(__middle, __last);
70 
71   return __last_iter;
72 }
73 
74 template <class _RandomAccessIterator, class _Compare>
75 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
76 void
77 partial_sort(_RandomAccessIterator __first, _RandomAccessIterator __middle, _RandomAccessIterator __last,
78              _Compare __comp)
79 {
80   static_assert(std::is_copy_constructible<_RandomAccessIterator>::value, "Iterators must be copy constructible.");
81   static_assert(std::is_copy_assignable<_RandomAccessIterator>::value, "Iterators must be copy assignable.");
82 
83   (void)std::__partial_sort<_ClassicAlgPolicy>(std::move(__first), std::move(__middle), std::move(__last), __comp);
84 }
85 
86 template <class _RandomAccessIterator>
87 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
88 void
89 partial_sort(_RandomAccessIterator __first, _RandomAccessIterator __middle, _RandomAccessIterator __last)
90 {
91     _VSTD::partial_sort(__first, __middle, __last,
92                         __less<typename iterator_traits<_RandomAccessIterator>::value_type>());
93 }
94 
95 _LIBCPP_END_NAMESPACE_STD
96 
97 #endif // _LIBCPP___ALGORITHM_PARTIAL_SORT_H
98