leetcode-mid-math -171. Excel Sheet Column Number

mycode   90.39%

class Solution(object):
    def titleToNumber(self, s):
        """
        :type s: str
        :rtype: int
        """
        res = 0
        for alpha in s:
            res = (ord(alpha) - 64) + res*26
        return res

参考：

carry实际上就是十进制中的指数

class Solution(object):
    def titleToNumber(self, s):
        """
        :type s: str
        :rtype: int
        """
        def _map(ch):
            chn = ord(ch) 
            assert chn >= ord('A') and chn <= ord('Z')
            return chn - ord('A') + 1
        lens = len(s)-1
        carry = 1
        val = 0
        while lens >=0:
            num = _map(s[lens])*carry
            val = val + num
            carry *= 26    
            lens -= 1
        return val