Excel Sheet Column Number

example：

    A -> 1
    B -> 2
    C -> 3
    ...
    Z -> 26
    AA -> 27
    AB -> 28 
"26进制 -> 10进制" 的转化

class Solution:
    # @param s, a string
    # @return an integer
    def titleToNumber(self, s):
        d=dict([('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)]);
        res=0
        num_char=len(s)
        for i in range(len(s)):
            res=res+d[s[i]]*pow(26,(num_char-i-1))
        print(res)
        return res

s=Solution()
s.titleToNumber("ZZZ")  # "ZZ" 702= 26*26+26