input: def diffHighestLowest(arr):
      """Calculate the difference between the highest and lowest values in an array of integers.
      >>> diffHighestLowest([12, 24, 3, 8, -1])
      25
      >>> diffHighestLowest([0, 0, 0, 0])
      0
      >>> diffHighestLowest([1, 1, 1, 1, 1])
      0
      """
output:     return max(arr) - min(arr)