random_permutation_iterator.hpp

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// (C) Copyright Renaud Detry   2007-2011.
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
 
#ifndef TRSL_RANDOM_PERMUTATION_ITERATOR_HPP
#define TRSL_RANDOM_PERMUTATION_ITERATOR_HPP
 
#include <trsl/reorder_iterator.hpp>
#include <trsl/common.hpp>
#include <trsl/error_handling.hpp>
 
namespace trsl
{
 
  template<class ElementIterator>
  reorder_iterator<ElementIterator>
  random_permutation_iterator(ElementIterator first,
                              ElementIterator last,
                              unsigned permutationSize)
  {
    ptrdiff_t size = std::distance(first, last);
    if (size < 0)
      throw bad_parameter_value(
        "random_permutation_iterator: "
        "bad input range.");
    if (permutationSize > unsigned(size))
      throw bad_parameter_value(
        "random_permutation_iterator: "
        "parameter permutationSize out of range.");
        
    typedef
      typename reorder_iterator<ElementIterator>::index_container
      index_container;
    typedef
      typename reorder_iterator<ElementIterator>::index_container_ptr
      index_container_ptr;
    typedef
      typename reorder_iterator<ElementIterator>::index_t
      index_t;
  
    index_container_ptr index_collection(new index_container);
        
    index_collection->resize(size);
    for (index_t i = 0; i < index_t(size); ++i)
      (*index_collection)[i] = i;
    if (permutationSize == unsigned(size))
      std::random_shuffle(index_collection->begin(),
                          index_collection->end(),
                          rand_gen::uniform_int);
    else
    {
      detail::partial_random_shuffle(index_collection->begin(),
                                     index_collection->begin()+permutationSize,
                                     index_collection->end(),
                                     rand_gen::uniform_int);
      index_collection->resize(permutationSize);
    }
    
    return reorder_iterator<ElementIterator>(first, index_collection);
  }
 
  template<class ElementIterator>
  reorder_iterator<ElementIterator>
  random_permutation_iterator(ElementIterator first,
                              ElementIterator last)
  {
    return random_permutation_iterator(first,
                                       last,
                                       std::distance(first, last));
  }
 
} // namespace trsl
 
#endif // include guard