input: def swap(arr1: List[int], arr2: List[int]) -> None:
      """ Swaps the elements of two arrays of the same length, element-wise.
      >>> arr1 = [3, 5, 6, 9]
      >>> arr2 = [2, 4, 7, 8]
      >>> swap(arr1, arr2)
      >>> arr1
      [2, 4, 7, 8]
      >>> arr2
      [3, 5, 6, 9]
      """
output:     for i in range(len(arr1)):
          arr1[i], arr2[i] = arr2[i], arr1[i]