input: Write a function that calculates the difference between the highest and lowest value in an array of integers. If the array is empty, return 0.
  def diffHighestLowest(arr):
      if not arr:
          return 0
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest
  assert diffHighestLowest([12, 24, 3, 8, -1])==25
  assert diffHighestLowest([4, 7, 2, 9, 1])==8
  assert diffHighestLowest([-5, -10, -2, -8])==8
  assert diffHighestLowest([5])==0
  assert diffHighestLowest([])==0
output: def diffHighestLowest(arr):
      if not arr:
          return 0
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest