Excel Sheet Column Number——Math

Related to question Excel Sheet Column Title

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 

class Solution(object):
    def titleToNumber(self, s):
        """
        :type s: str
        :rtype: int
        """
        tag = {'A':1,  'B':2,  'C':3,  'D':4,  'E':5, 
               'F':6,  'G':7,  'H':8,  'I':9,  'J':10, 
               'K':11, 'L':12, 'M':13, 'N':14, 'O':15, 
               'P':16, 'Q':17, 'R':18, 'S':19, 'T':20, 
               'U':21, 'V':22, 'W':23, 'X':24, 'Y':25, 'Z':26 }
        re = 0
        n = len(s)-1
        for i in range(len(s)):
        	re += tag[s[i]] * 26**n
        	n -= 1
        return re