27 Algorithms library [algorithms]

27.7 Mutating sequence operations [alg.modifying.operations]

27.7.13 Shuffle [alg.random.shuffle]

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

template<random_access_iterator I, sentinel_for<I> S, class Gen>
  requires permutable<I> &&
           uniform_random_bit_generator<remove_reference_t<Gen>>
  I ranges::shuffle(I first, S last, Gen&& g);
template<random_access_range R, class Gen>
  requires permutable<iterator_t<R>> &&
           uniform_random_bit_generator<remove_reference_t<Gen>>
  borrowed_iterator_t<R> ranges::shuffle(R&& r, Gen&& g);

Preconditions: For the overload in namespace std:

(1.1)
RandomAccessIterator meets the Cpp17ValueSwappable requirements ([swappable.requirements]).
(1.2)
The type remove_reference_t<UniformRandomBitGenerator> meets the uniform random bit generator ([rand.req.urng]) requirements.

Effects: Permutes the elements in the range [first, last) such that each possible permutation of those elements has equal probability of appearance.

Returns: last for the overloads in namespace ranges.

Complexity: Exactly (last - first) - 1 swaps.

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.