input: def swap(arr1: List[int], arr2: List[int]):
      """ Take two array of integers and swap their elements.
      >>> swap([3, 5, 6, 9], [2, 4, 7, 8])
      """
output:     for i in range(len(arr1)):
          arr1[i], arr2[i] = arr2[i], arr1[i]