Simple quicksort in Ruby, just as an exercise.

quicksort.rb

def quicksort(array, first = true)

  if first == true
    # if this is the first time quicksort is invoked
    # we have to de-reference the array, as we use the
    # destructive method delete_at
    array = array.dup
  end

  if array.size <= 1
    return array
  end

  pivot = array[rand(array.size)]
  array.delete_at(array.index(pivot))

  less, greater = [], []

  array.each do |x|
    if x <= pivot
      less << x
    else
      greater << x
    end
  end
  
  return [quicksort(less, false), pivot, quicksort(greater, false)].flatten
end 

@array = Array.new(9).map { rand(99) }
puts "Unsorted array:\t#{@array}"

@sorted_array = quicksort(@array)
puts "Sorted array:\t\t#{@sorted_array}"