quicksort called with arr = [3, 2, 1]
quicksort called with arr = [2, 1]
quicksort called with arr = [1]
quicksort called with arr = []
quicksort returned with []
quicksort called with arr = []
quicksort returned with []
quicksort returned with [1]
quicksort called with arr = []
quicksort returned with []
quicksort returned with [1, 2]
quicksort called with arr = []
quicksort returned with []
quicksort returned with [1, 2, 3]