Ruby quicksort

quicksort.rb

# The steps are:
#   1. Pick an element, called a pivot, from the array.
#   2. Reorder the array so that all elements with values less than the pivot come before the pivot, while all elements with # #      values greater than the pivot come after it (equal values can go either way). After this partitioning, the pivot is in  #      its final position. This is called the partition operation.
#   3. Recursively apply the above steps to the sub-array of elements with smaller values and separately to the sub-array of   #      elements with greater values.


class Array
  def quicksort
    return [] if empty?
    # 1
    pivot = delete_at(rand(size))
    # 2
    left, right = partition(&pivot.method(:>))
    # 3
    return *left.quicksort, pivot, *right.quicksort
  end
end