input: Write a function to calculate the difference between the lowest and highest value for an array of integers. Return the difference.
  def diffHighestLowest(arr):
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest
  
  assert diffHighestLowest([12, 24, 3, 8, -1])==25
  assert diffHighestLowest([0, 0, 0, 0])==0
  assert diffHighestLowest([45, 12, 78, -9])==87
  assert diffHighestLowest([-12, -8, -3, -20])==8
  assert diffHighestLowest([])==0
output: def diffHighestLowest(arr):
      if not arr:
          return 0
      lowest = min(arr)
      highest = max(arr)
      return highest - lowest