Quick Sort advance in Ruby

quick-sort-advance.rb

def advanced_quicksort(array)

  def helper(array, start=0, last=array.size-1)
    return array if last-start < 1
    pivot = array[last]
    middle = start - 1

    for i in start..last
    array[i] <= pivot ? (middle += 1; array[i], array[middle] = array[middle], array[i] ) : array[i]
    end
    # puts array.join(" ")
    helper(array, start, middle-1)
    helper(array, middle+1, last)
  end

  result = array.dup

  helper(result)  
  
end