input: Write a function to calculate the difference between the lowest and highest value for an array of integers. Return the difference between the highest and lowest values. If the array is empty, return 0.
  def diffHighestLowest(arr):
      if len(arr) == 0:
          return 0
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest
  
  assert diffHighestLowest([12, 24, 3, 8, -1]) == 25
  assert diffHighestLowest([-30, -10, -20]) == 20
  assert diffHighestLowest([]) == 0
  assert diffHighestLowest([5]) == 0
output: def diffHighestLowest(arr):
      if len(arr) == 0:
          return 0
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest