input: Write a python function to calculate the number of replacement transformations between two strings.
  assert replacement_transformations('hello', 'world') == 24
  assert replacement_transformations('abc', 'def') == 9
  assert replacement_transformations('a', 'a') == 1
output: def replacement_transformations(s1, s2):
      if len(s1) != len(s2):
          return 0
      transformations = 1
      for char1, char2 in zip(s1, s2):
          if char1 != char2:
              transformations *= 3
      return transformations