[alg.random.shuffle]

# 26 Algorithms library [[algorithms]](./#algorithms)

## 26.7 Mutating sequence operations [[alg.modifying.operations]](alg.modifying.operations#alg.random.shuffle)

### 26.7.13 Shuffle [alg.random.shuffle]

[🔗](#lib:shuffle)

`template<class RandomAccessIterator, class UniformRandomBitGenerator>
  void shuffle(RandomAccessIterator first,
               RandomAccessIterator last,
               UniformRandomBitGenerator&& g);

template<[random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, class Gen>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<I> &&
           [uniform_random_bit_generator](rand.req.urng#concept:uniform_random_bit_generator "29.5.3.3 Uniform random bit generator requirements [rand.req.urng]")<remove_reference_t<Gen>>
  I ranges::shuffle(I first, S last, Gen&& g);
template<[random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]") R, class Gen>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>> &&
           [uniform_random_bit_generator](rand.req.urng#concept:uniform_random_bit_generator "29.5.3.3 Uniform random bit generator requirements [rand.req.urng]")<remove_reference_t<Gen>>
  borrowed_iterator_t<R> ranges::shuffle(R&& r, Gen&& g);
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8491)

*Preconditions*: For the overload in namespace std:

- [(1.1)](#1.1)

  RandomAccessIterator meets
 the [*Cpp17ValueSwappable*](swappable.requirements#:Cpp17ValueSwappable "16.4.4.3 Swappable requirements [swappable.requirements]") requirements ([[swappable.requirements]](swappable.requirements "16.4.4.3 Swappable requirements"))[.](#1.1.sentence-1)

- [(1.2)](#1.2)

  The type remove_reference_t<UniformRandomBitGenerator> meets
 the uniform random bit generator ([[rand.req.urng]](rand.req.urng "29.5.3.3 Uniform random bit generator requirements")) requirements[.](#1.2.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8503)

*Effects*: Permutes the elements in the range [first, last)
such that each possible permutation of those elements
has equal probability of appearance[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8509)

*Returns*: last for the overloads in namespace ranges[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8513)

*Complexity*: Exactly (last - first) - 1 swaps[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8517)

*Remarks*: To the extent that the implementation of this function makes use
of random numbers, the object referenced by g shall serve as
the implementation's source of randomness[.](#5.sentence-1)