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_PUSH_MACROS
  26 #include <__undef_macros>
  27
  28 _LIBCPP_BEGIN_NAMESPACE_STD
  29
  30 template <class _AlgPolicy, class _Compare, class _BidirectionalIterator, class _Sentinel>
  31 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_BidirectionalIterator, bool>
  32 __prev_permutation(_BidirectionalIterator __first, _Sentinel __last, _Compare&& __comp) {
  33   using _Result = pair<_BidirectionalIterator, bool>;
  34
  35   _BidirectionalIterator __last_iter = _IterOps<_AlgPolicy>::next(__first, __last);
  36   _BidirectionalIterator __i         = __last_iter;
  37   if (__first == __last || __first == --__i)
  38     return _Result(std::move(__last_iter), false);
  39
  40   while (true) {
  41     _BidirectionalIterator __ip1 = __i;
  42     if (__comp(*__ip1, *--__i)) {
  43       _BidirectionalIterator __j = __last_iter;
  44       while (!__comp(*--__j, *__i))
  45         ;
  46       _IterOps<_AlgPolicy>::iter_swap(__i, __j);
  47       std::__reverse<_AlgPolicy>(__ip1, __last_iter);
  48       return _Result(std::move(__last_iter), true);
  49     }
  50     if (__i == __first) {
  51       std::__reverse<_AlgPolicy>(__first, __last_iter);
  52       return _Result(std::move(__last_iter), false);
  53     }
  54   }
  55 }
  56
  57 template <class _BidirectionalIterator, class _Compare>
  58 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
  59 prev_permutation(_BidirectionalIterator __first, _BidirectionalIterator __last, _Compare __comp) {
  60   return std::__prev_permutation<_ClassicAlgPolicy>(
  61              std::move(__first), std::move(__last), static_cast<__comp_ref_type<_Compare> >(__comp))
  62       .second;
  63 }
  64
  65 template <class _BidirectionalIterator>
  66 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
  67 prev_permutation(_BidirectionalIterator __first, _BidirectionalIterator __last) {
  68   return std::prev_permutation(__first, __last, __less<>());
  69 }
  70
  71 _LIBCPP_END_NAMESPACE_STD
  72
  73 _LIBCPP_POP_MACROS
  74
  75 #endif // _LIBCPP___ALGORITHM_PREV_PERMUTATION_H