libcxx/include/__algorithm/prev_permutation.h

   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