Ruby quicksort

gistfile1.txt

module Enumerable
  def quicksort()
    if size <= 1
      self
    else
      pivot = shift
      lower, greater = partition {|x| x < pivot }.map(&:quicksort)
      lower.push(pivot).concat(greater)
    end
  end
end

You need >= in the upper check, otherwise if the pivot is duplicated, then the other values that are the same will be dropped.