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_PREV_PERMUTATION_H
10 #define _LIBCPP___ALGORITHM_PREV_PERMUTATION_H
11 
12 #include <__algorithm/comp.h>
13 #include <__algorithm/comp_ref_type.h>
14 #include <__algorithm/iterator_operations.h>
15 #include <__algorithm/reverse.h>
16 #include <__config>
17 #include <__iterator/iterator_traits.h>
18 #include <__utility/move.h>
19 #include <__utility/pair.h>
20 
21 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
22 #  pragma GCC system_header
23 #endif
24 
25 _LIBCPP_BEGIN_NAMESPACE_STD
26 
27 template <class _AlgPolicy, class _Compare, class _BidirectionalIterator, class _Sentinel>
28 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
29 pair<_BidirectionalIterator, bool>
30 __prev_permutation(_BidirectionalIterator __first, _Sentinel __last, _Compare&& __comp)
31 {
32     using _Result = pair<_BidirectionalIterator, bool>;
33 
34     _BidirectionalIterator __last_iter = _IterOps<_AlgPolicy>::next(__first, __last);
35     _BidirectionalIterator __i = __last_iter;
36     if (__first == __last || __first == --__i)
37         return _Result(std::move(__last_iter), false);
38 
39     while (true)
40     {
41         _BidirectionalIterator __ip1 = __i;
42         if (__comp(*__ip1, *--__i))
43         {
44             _BidirectionalIterator __j = __last_iter;
45             while (!__comp(*--__j, *__i))
46                 ;
47             _IterOps<_AlgPolicy>::iter_swap(__i, __j);
48             std::__reverse<_AlgPolicy>(__ip1, __last_iter);
49             return _Result(std::move(__last_iter), true);
50         }
51         if (__i == __first)
52         {
53             std::__reverse<_AlgPolicy>(__first, __last_iter);
54             return _Result(std::move(__last_iter), false);
55         }
56     }
57 }
58 
59 template <class _BidirectionalIterator, class _Compare>
60 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
61 bool
62 prev_permutation(_BidirectionalIterator __first, _BidirectionalIterator __last, _Compare __comp)
63 {
64   return std::__prev_permutation<_ClassicAlgPolicy>(
65       std::move(__first), std::move(__last), static_cast<__comp_ref_type<_Compare> >(__comp)).second;
66 }
67 
68 template <class _BidirectionalIterator>
69 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
70 bool
71 prev_permutation(_BidirectionalIterator __first, _BidirectionalIterator __last)
72 {
73     return _VSTD::prev_permutation(__first, __last, __less<>());
74 }
75 
76 _LIBCPP_END_NAMESPACE_STD
77 
78 #endif // _LIBCPP___ALGORITHM_PREV_PERMUTATION_H
79