40Excel表列序号

给定一个Excel表格中的列名称，返回其相应的列序号。
例如，
A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28
...

示例 1:
输入: "A"
输出: 1

示例 2:
输入: "AB"
输出: 28

示例 3:
输入: "ZY"
输出: 701

二十六进制转十进制

class Solution:
    def titleToNumber(self, s: str) -> int:
        res = 0
        bit = 1
        for a in s[::-1]:
            res += (ord(a) - 64) * bit
            bit *= 26
        return res

哈希表

class Solution:
    def titleToNumber(self, s: str) -> int:
        d = len(s)
        value = 0
        sdict = {}
        for i in range(1, 27):
            sdict[chr(i+64)] = i
        for i in s:
            if d > 0:
                value += sdict[i] * 26**(d-1)
                d -= 1
        return value

import functools
class Solution:
    def titleToNumber(self, s: str) -> int:
        return functools.reduce(lambda x, y: x * 26 + y, [ord(a) - 64 for a in s ])

class Solution:
    def titleToNumber(self, s: str) -> int:
        return sum( (ord(a) - 64) * (26 ** i)  for i, a in enumerate(s[::-1]))

来源：力扣（LeetCode）