Given a column title as appear in an Excel sheet, return its corresponding column number.
For example:
    A -> 1
    B -> 2
    C -> 3
    ...
    Z -> 26
    AA -> 27
    AB -> 28 
    ...
Example 1:
Input: "A"
Output: 1
Example 2:
Input: "AB"
Output: 28
Example 3:
Input: "ZY"
Output: 701
class Solution:
     def titleToNumber(self, s):
         """
         :type s: str
         :rtype: int
         """
         if s == "":
             return 0
         return self.titleToNumber(s[:-1])*26 + ord(s[-1]) - ord('A') + 1
class Solution:
     def titleToNumber(self, s):
         """
         :type s: str
         :rtype: int
         """
         if s == "":
             return 0
         return self.titleToNumber(s[:-1])*26 + ord(s[-1]) - ord('A') + 1