leetcode 之 Excel Sheet Column Number

题目描述:
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 

意思是将一个字符串转成相应的数字,其转换规则是 excel表格计数那样, A->1 AA->27 

稍稍分析得知, 其实是一个26进制的问题, 容易得出: AA = 26^1*nums(A) + 26^0*nums(A)  ABC= 26^2*nums(A)+26^1*nums(B)+....

代码如下：

class Solution(object):
    def titleToNumber(self, s):
        """
        :type s: str
        :rtype: int
        """
        l = len(s)
        num = 0
        for i in range(0, l):
            num += (26**(l-i-1))*(ord(s[i])-64)
        return num