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random_shuffle
PrototypeRandom_shuffle is an overloaded name; there are actually two random_shuffle functions.template <class RandomAccessIterator> void random_shuffle(RandomAccessIterator first, RandomAccessIterator last); template <class RandomAccessIterator, class RandomNumberGenerator> void random_shuffle(RandomAccessIterator first, RandomAccessIterator last, RandomNumberGenerator& rand) DescriptionRandom_shuffle randomly rearranges the elements in the range [first, last): that is, it randomly picks one of the N! possible orderings, where N is last  first. [1] There are two different versions of random_shuffle. The first version uses an internal random number generator, and the second uses a Random Number Generator, a special kind of function object, that is explicitly passed as an argument.DefinitionDefined in the standard header algorithm, and in the nonstandard backwardcompatibility header algo.h.Requirements on typesFor the first version:
Preconditions
ComplexityLinear in last  first. If last != first, exactly (last  first)  1 swaps are performed.Exampleconst int N = 8; int A[] = {1, 2, 3, 4, 5, 6, 7, 8}; random_shuffle(A, A + N); copy(A, A + N, ostream_iterator<int>(cout, " ")); // The printed result might be 7 1 6 3 2 5 4 8, // or any of 40,319 other possibilities. Notes[1] This algorithm is described in section 3.4.2 of Knuth (D. E. Knuth, The Art of Computer Programming. Volume 2: Seminumerical Algorithms, second edition. AddisonWesley, 1981). Knuth credits Moses and Oakford (1963) and Durstenfeld (1964). Note that there are N! ways of arranging a sequence of N elements. Random_shuffle yields uniformly distributed results; that is, the probability of any particular ordering is 1/N!. The reason this comment is important is that there are a number of algorithms that seem at first sight to implement random shuffling of a sequence, but that do not in fact produce a uniform distribution over the N! possible orderings. That is, it's easy to get random shuffle wrong. See alsorandom_sample, random_sample_n, next_permutation, prev_permutation, Random Number GeneratorCopyright © 1999 Silicon Graphics, Inc. All Rights Reserved. TrademarkInformation
