171. Excel Sheet Column Number

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 
...

Example 1:

Input: "A" Output: 1 Example 2:

Input: "AB" Output: 28 Example 3:

Input: "ZY" Output: 701

思路：倒转s，切片*26

代码：python3

class Solution:
    def titleToNumber(self, s: str) -> int:
        revStr = s[::-1]
        num=0
        for i, ch in enumerate(revStr):
            num = num+(ord(ch)-64)*pow(26, i)
        return num