input: def bubble_sort(arr: List[int]) -> None:
      """ Sorts the given array in ascending order using bubble sort algorithm.
      >>> arr = [3, 7, 4, 1]
      >>> bubble_sort(arr)
      >>> arr
      [1, 3, 4, 7]
      """
output:     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]