input: Write a function to compute the absolute difference between two given numbers. If the numbers are the same, the function should return 0.
  assert absolute_difference(9, 5)==4
  assert absolute_difference(5, 9)==4
  assert absolute_difference(5, 5)==0
  assert absolute_difference(-3, 3)==6
  assert absolute_difference(0, 0)==0
output: def absolute_difference(a, b):
      if a == b:
          return 0
      return abs(a - b)