input: def editDistance(string1: str, string2: str, m: int, n: int) -> int:
      """ Compute the edit distance between two strings.
      >>> editDistance("kitten", "sitting", 6, 7)
      3
      >>> editDistance("horse", "ros", 5, 3)
      3
      """
output:     if m == 0:
          return n
      if n == 0:
          return m
      if string1[m-1] == string2[n-1]:
          return editDistance(string1, string2, m-1, n-1)
      return 1 + min(editDistance(string1, string2, m, n-1),
                     editDistance(string1, string2, m-1, n),
                     editDistance(string1, string2, m-1, n-1))