input: def editDistance(string1, string2, m, n):
      """ Compute the edit distance between two strings.
      >>> editDistance("kitten", "sitting", 6, 7)
      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),    # Insert
                     editDistance(string1, string2, m-1, n),    # Remove
                     editDistance(string1, string2, m-1, n-1))  # Replace