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. The function should take an array of integers as input and return the difference as an integer.
  assert diffHighestLowest([12, 24, 3, 8, -1]) == 25
  assert diffHighestLowest([-5, 0, 5]) == 10
  assert diffHighestLowest([]) == 0
  assert diffHighestLowest([7]) == 0
  assert diffHighestLowest([10, -20, 30, 40]) == 60
output: def diffHighestLowest(arr):
      if not arr:
          return 0
      return max(arr) - min(arr)