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.
  
  assert diffHighestLowest([12, 24, 3, 8, -1])==25
  assert diffHighestLowest([5, 10, 15, 20])==15
  assert diffHighestLowest([-5, -10, -15, -20])==15
  assert diffHighestLowest([])==0
  assert diffHighestLowest([1])==0
output: def diffHighestLowest(arr):
      if not arr:
          return 0
      return max(arr) - min(arr)