input: Write a function to calculate the difference between the lowest and highest value for 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([-5, -3, -7, -2]) == 5
  assert diffHighestLowest([0, 0, 0, 0]) == 0
  assert diffHighestLowest([]) == 0
output: def diffHighestLowest(arr):
      if not arr:
          return 0
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest