input: def diffHighestLowest(arr: List[int]) -> int:
      """ Calculate the difference between the lowest and highest value in an array of integers.
      >>> diffHighestLowest([12, 24, 3, 8, -1])
      25
      >>> diffHighestLowest([1, 2, 3, 4, 5])
      4
      """
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest
output:     lowest = min(arr)
      highest = max(arr)
      return highest - lowest