return a if a.size 2

    (x = a.pop) ?  quick_sort(a.select{|i| i =x }) + [x] + quick_sort(a.select{|i| i > x}) : []

end

array = [72,6,57,88,60,42,83,73,42,48,85]

p quick_sort(array)    #=> [6, 42, 42, 48, 57, 60, 72, 73, 83, 85, 88]