random_shuffle

Randomize a sequence using random shuffles.

Shuffle all elements in the sequence [ first ... last ) using uniformly selected random swaps. Use operator= to perform the swaps. The first version uses an internal random number generator to generate the indices of the elements to swap, whereas the second version uses the random number generator rand . The parameter rand must be a random number generator that takes a parameter n and returns an integral random number between 0 and ( n - 1 ).

Library

Standards<ToolKit>

Declaration


#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
  );

Complexity

Time complexity is linear as ( last - first ) swaps are performed. Space complexity is constant.

Example <ospace/osstd/examples/rndshuf0.cpp>
#include <iostream>
#include <algorithm>

int numbers[ 6 ] = { 1, 2, 3, 4, 5, 6 };

void
main()
  {
  random_shuffle( numbers, numbers + 6 );

  for ( int i = 0; i < 6; ++i )
    cout << numbers[ i ] << ` `;
  cout << "\n";
  }

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Example <ospace/osstd/examples/rndshuf1.cpp>
#include <iostream>
#include <algorithm>
#include <iterator>
#include <vector>

void
main()
  {
  vector< int > v1( 10 );
  for ( size_t j = 0; j < v1.size(); ++j )
    v1[ j ] = j;
  ostream_iterator< int > iter( cout, " " );
  copy( v1.begin(), v1.end(), iter );
  cout << "\n";

  for ( int i = 0; i < 3; ++i )
    {
    random_shuffle( v1.begin(), v1.end() );

    copy( v1.begin(), v1.end(), iter );
    cout << "\n";
    }
  }

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Example <ospace/osstd/examples/rndshuf2.cpp>
#include <iostream>
#include <stdlib.h>
#include <algorithm>
#include <iterator>
#include <vector>

class MyRandomGenerator
  {
  public:
    unsigned long operator() (unsigned long n_ );
  };

unsigned long
MyRandomGenerator::operator() (unsigned long n_ )
  {
  return rand() % n_;
  }

void
main()
  {
  vector< int > v1( 10 );
  for ( size_t j = 0; j < v1.size(); ++j )
    v1[ j ] = j;
  ostream_iterator< int > iter( cout, " " );
  copy( v1.begin(), v1.end(), iter );
  cout << "\n";
  MyRandomGenerator r;

  for ( int i = 0; i < 3; ++i )
    {
    random_shuffle( v1.begin(), v1.end(), r );

    copy( v1.begin(), v1.end(), iter );
    cout << "\n";
    }
  }

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