input: Write a python function to implement bubble sort.
  assert bubbleSort([5, 4, 2, 1, 3])==[1, 2, 3, 4, 5]
  assert bubbleSort([10, 7, 3, 8, 4, 2])==[2, 3, 4, 7, 8, 10]
  assert bubbleSort([1, 9, 8, 7, 6, 5])==[1, 5, 6, 7, 8, 9]
output: def bubbleSort(arr):
      n = len(arr)
      for i in range(n):
          for j in range(0, n-i-1):
              if arr[j] > arr[j+1]:
                  arr[j], arr[j+1] = arr[j+1], arr[j]
      return arr