random_shuffle

     Algorithm

Randomly shuffles elements of a collection.

Contents

• Synopsis
• Description
• Complexity
• Example
• Warning

#include <algorithm>

template <class RandomAccessIterator>
 void random_shuffle (RandomAccessIterator first,
                      RandomAccessIterator last);
template <class RandomAccessIterator,
          class RandomNumberGenerator>
 void random_shuffle (RandomAccessIterator first,
                      RandomAccessIterator last,
                      RandomNumberGenerator& rand);

The random_shuffle algorithm shuffles the elements in the range [first, last) with uniform distribution. random_shuffle can take a particular random number generating function object rand , where rand takes a positive argument n of distance type of the RandomAccessIterator and returns a randomly chosen value between 0 and n - 1.

In the random_shuffle algorithm, (last - first) -1 swaps are done.

//
// rndshufl.cpp
//
 #include <algorithm>
 #include <vector>
 #include <iostream.h>

 int main()
 {
   //Initialize a vector with an array of ints
   int arr[10] = {1,2,3,4,5,6,7,8,9,10};
   vector<int> v(arr, arr+10);

   //Print out elements in original (sorted) order
   cout << "Elements before random_shuffle: " << endl << "     ";
   copy(v.begin(),v.end(),ostream_iterator<int>(cout," "));
   cout << endl << endl;

   //Mix them up with random_shuffle
   random_shuffle(v.begin(), v.end());

   //Print out the mixed up elements
   cout << "Elements after random_shuffle: " << endl << "     ";
   copy(v.begin(),v.end(),ostream_iterator<int>(cout," "));
   cout << endl;
   return 0;
 }
Output :
Elements before random_shuffle:
     1 2 3 4 5 6 7 8 9 10
Elements after random_shuffle:
     7 9 10 3 2 5 4 8 1 6

If your compiler does not support default template parameters, you need to always supply the Allocator template argument. For instance, you will need to write :

vector<int, allocator>

instead of :

vector<int>