random_shuffle()

Library:  Algorithms

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Algorithm that randomly shuffles elements of a collection

#include <algorithm>

namespace std {
  template <class RandomAccessIterator>
  void random_shuffle(RandomAccessIterator start,
                      RandomAccessIterator finish);

  template <class RandomAccessIterator,
            class RandomNumberGenerator>
  void random_shuffle(RandomAccessIterator start,
                      RandomAccessIterator finish,
                      RandomNumberGenerator& rand);
}

The random_shuffle() algorithm shuffles the elements in the range [start, finish) with uniform distribution. random_shuffle() can take a particular random number generating function object rand (where rand takes a positive argument n of type convertible from std::iterator_traits<RandomAccessIterator>::difference_type) and returns a randomly chosen value between 0 and n - 1.

In the random_shuffle() algorithm, (finish - start) - 1 swaps are done.

//
//  rndshufl.cpp
//

#include <algorithm>   // for random_shuffle
#include <iostream>    // for cout, endl
#include <iterator>    // for ostream_iterator
#include <string>      // for string



int main ()
{
    // Create a string of doubles (unusual? maybe, 
    // but why not...)
    typedef std::basic_string<double, 
                              std::char_traits<double>,
                              std::allocator<double> >
            Bizarre;

    // Initialize a Bizarre with an array of values.
    const Bizarre::value_type a[] = { 1, 2, 3, 4, 5, 
                                      6, 7, 8, 9, 10 };

    Bizarre b (a + 0, a + sizeof a / sizeof *a);

    typedef std::ostream_iterator<double, char, 
                                  std::char_traits<char> >
            Iter;

    // Suppress decimal point in output.
    std::cout.precision (0);

    // Print out elements in original (sorted) order.
    std::cout << "Elements before random_shuffle: \n     ";
    std::copy (b.begin (), b.end (), Iter (std::cout," "));

    // Mix them up with random_shuffle.
    std::random_shuffle (b.begin (), b.end ());

    // Print out the mixed up elements.
    std::cout << "\n\nElements after random_shuffle: \n     ";
    std::copy (b.begin (), b.end (), Iter (std::cout, " "));
    std::cout << std::endl;

    return 0;
}


Program Output:

Elements before random_shuffle: 
     1 2 3 4 5 6 7 8 9 10 

Elements after random_shuffle: 
     9 8 7 6 2 3 1 4 5 10 

ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 25.2.11