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