input: from typing import List
  
  def swap(arr1: List[int], arr2: List[int]) -> None:
      """ Swap elements of two arrays.
      >>> swap([3, 5, 6, 9], [2, 4, 7, 8])
      >>> arr1 = [2, 4, 7, 8]
      >>> arr2 = [3, 5, 6, 9]
      """
      assert len(arr1) == len(arr2)
      for i in range(len(arr1)):
          temp = arr1[i]
          arr1[i] = arr2[i]
          arr2[i] = temp
output:     assert len(arr1) == len(arr2)
      for i in range(len(arr1)):
          temp = arr1[i]
          arr1[i] = arr2[i]
          arr2[i] = temp