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[alg.reverse]
# 26 Algorithms library [[algorithms]](./#algorithms)
## 26.7 Mutating sequence operations [[alg.modifying.operations]](alg.modifying.operations#alg.reverse)
### 26.7.10 Reverse [alg.reverse]
[🔗](#lib:reverse)
`template<class BidirectionalIterator>
constexpr void reverse(BidirectionalIterator first, BidirectionalIterator last);
template<class ExecutionPolicy, class BidirectionalIterator>
void reverse(ExecutionPolicy&& exec,
BidirectionalIterator first, BidirectionalIterator last);
template<[bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12Concept bidirectional_­iterator[iterator.concept.bidir]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7Concept sentinel_­for[iterator.concept.sentinel]")<I> S>
requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6Concept permutable[alg.req.permutable]")<I>
constexpr I ranges::reverse(I first, S last);
template<[bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6Other range refinements[range.refinements]") R>
requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6Concept permutable[alg.req.permutable]")<iterator_t<R>>
constexpr borrowed_iterator_t<R> ranges::reverse(R&& r);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1Preamble[algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13Concept random_­access_­iterator[iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8Concept sized_­sentinel_­for[iterator.concept.sizedsentinel]")<I> S>
requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6Concept permutable[alg.req.permutable]")<I>
I ranges::reverse(Ep&& exec, I first, S last);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1Preamble[algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6Other range refinements[range.refinements]") R>
requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6Concept permutable[alg.req.permutable]")<iterator_t<R>>
borrowed_iterator_t<R> ranges::reverse(Ep&& exec, R&& r);
`
[1](#1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8064)
*Preconditions*: For the overloads in namespace std,BidirectionalIterator meets
the [*Cpp17ValueSwappable*](swappable.requirements#:Cpp17ValueSwappable "16.4.4.3Swappable requirements[swappable.requirements]") requirements ([[swappable.requirements]](swappable.requirements "16.4.4.3Swappable requirements"))[.](#1.sentence-1)
[2](#2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8070)
*Effects*: For each non-negative integer i < (last - first) / 2,
applies std::iter_swap, orranges::iter_swap for the overloads in namespace ranges,
to all pairs of iterators first + i, (last - i) - 1[.](#2.sentence-1)
[3](#3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8077)
*Returns*: last for the overloads in namespace ranges[.](#3.sentence-1)
[4](#4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8081)
*Complexity*: Exactly (last - first)/2 swaps[.](#4.sentence-1)
[🔗](#lib:reverse_copy)
`template<class BidirectionalIterator, class OutputIterator>
constexpr OutputIterator
reverse_copy(BidirectionalIterator first, BidirectionalIterator last,
OutputIterator result);
template<class ExecutionPolicy, class BidirectionalIterator, class ForwardIterator>
ForwardIterator
reverse_copy(ExecutionPolicy&& exec,
BidirectionalIterator first, BidirectionalIterator last,
ForwardIterator result);
template<[bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12Concept bidirectional_­iterator[iterator.concept.bidir]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7Concept sentinel_­for[iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4Concept weakly_­incrementable[iterator.concept.winc]") O>
requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3Concept indirectly_­copyable[alg.req.ind.copy]")<I, O>
constexpr ranges::reverse_copy_result<I, O>
ranges::reverse_copy(I first, S last, O result);
template<[bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6Other range refinements[range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4Concept weakly_­incrementable[iterator.concept.winc]") O>
requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3Concept indirectly_­copyable[alg.req.ind.copy]")<iterator_t<R>, O>
constexpr ranges::reverse_copy_result<borrowed_iterator_t<R>, O>
ranges::reverse_copy(R&& r, O result);
`
[5](#5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8109)
Let N be last - first[.](#5.sentence-1)
[6](#6)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8112)
*Preconditions*: The ranges [first, last) and [result, result + N)
do not overlap[.](#6.sentence-1)
[7](#7)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8117)
*Effects*: Copies the range [first, last) to the range [result, result + N)
such that for every non-negative integer i < N the following assignment takes place:*(result + N - 1 - i) = *(first + i)[.](#7.sentence-1)
[8](#8)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8124)
*Returns*:
- [(8.1)](#8.1)
result + N for the overloads in namespace std[.](#8.1.sentence-1)
- [(8.2)](#8.2)
{last, result + N} for the overloads in namespace ranges[.](#8.2.sentence-1)
[9](#9)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8133)
*Complexity*: Exactly N assignments[.](#9.sentence-1)
[🔗](#itemdecl:3)
`template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1Preamble[algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13Concept random_­access_­iterator[iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8Concept sized_­sentinel_­for[iterator.concept.sizedsentinel]")<I> S,
[random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13Concept random_­access_­iterator[iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8Concept sized_­sentinel_­for[iterator.concept.sizedsentinel]")<O> OutS>
requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3Concept indirectly_­copyable[alg.req.ind.copy]")<I, O>
ranges::reverse_copy_truncated_result<I, O>
ranges::reverse_copy(Ep&& exec, I first, S last, O result,
OutS result_last);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1Preamble[algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6Other range refinements[range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6Other range refinements[range.refinements]") OutR>
requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3Concept indirectly_­copyable[alg.req.ind.copy]")<iterator_t<R>, iterator_t<OutR>>
ranges::reverse_copy_truncated_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
ranges::reverse_copy(Ep&& exec, R&& r, OutR&& result_r);
`
[10](#10)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8152)
Let N be min(last - first, result_last - result),
and let *NEW_FIRST* be first + (last - first) - N[.](#10.sentence-1)
[11](#11)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8156)
*Preconditions*: The ranges [first, last) and [result, result + N)
do not overlap[.](#11.sentence-1)
[12](#12)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8161)
*Effects*: Copies the range [*NEW_FIRST*, last)
to the range [result, result + N)
such that for every non-negative integer i<N the following assignment takes place:*(result + N - 1 - i) = *(*NEW_FIRST* + i)[.](#12.sentence-1)
[13](#13)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8169)
*Returns*: {last, *NEW_FIRST*, result + N}[.](#13.sentence-1)
[14](#14)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8173)
*Complexity*: Exactly N assignments[.](#14.sentence-1)