Category: algorithms | Component type: function |
template <class RandomAccessIterator> void random_shuffle(RandomAccessIterator first, RandomAccessIterator last); template <class RandomAccessIterator, class RandomNumberGenerator> void random_shuffle(RandomAccessIterator first, RandomAccessIterator last, RandomNumberGenerator& rand)
const 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.
[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. Addison-Wesley, 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.
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