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/reverse.h>
15 #include <__config>
16 #include <__iterator/iterator_traits.h>
17 #include <__utility/swap.h>
18 
19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
20 #pragma GCC system_header
21 #endif
22 
23 _LIBCPP_BEGIN_NAMESPACE_STD
24 
25 template <class _Compare, class _BidirectionalIterator>
26 _LIBCPP_CONSTEXPR_AFTER_CXX17 bool
27 __prev_permutation(_BidirectionalIterator __first, _BidirectionalIterator __last, _Compare __comp)
28 {
29     _BidirectionalIterator __i = __last;
30     if (__first == __last || __first == --__i)
31         return false;
32     while (true)
33     {
34         _BidirectionalIterator __ip1 = __i;
35         if (__comp(*__ip1, *--__i))
36         {
37             _BidirectionalIterator __j = __last;
38             while (!__comp(*--__j, *__i))
39                 ;
40             swap(*__i, *__j);
41             _VSTD::reverse(__ip1, __last);
42             return true;
43         }
44         if (__i == __first)
45         {
46             _VSTD::reverse(__first, __last);
47             return false;
48         }
49     }
50 }
51 
52 template <class _BidirectionalIterator, class _Compare>
53 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
54 bool
55 prev_permutation(_BidirectionalIterator __first, _BidirectionalIterator __last, _Compare __comp)
56 {
57     typedef typename __comp_ref_type<_Compare>::type _Comp_ref;
58     return _VSTD::__prev_permutation<_Comp_ref>(__first, __last, __comp);
59 }
60 
61 template <class _BidirectionalIterator>
62 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
63 bool
64 prev_permutation(_BidirectionalIterator __first, _BidirectionalIterator __last)
65 {
66     return _VSTD::prev_permutation(__first, __last,
67                                   __less<typename iterator_traits<_BidirectionalIterator>::value_type>());
68 }
69 
70 _LIBCPP_END_NAMESPACE_STD
71 
72 #endif // _LIBCPP___ALGORITHM_PREV_PERMUTATION_H
73