171. Excel Sheet Column Number-Excel表列序号

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

Constraints:

• 1 <= s.length <= 7
• s consists only of uppercase English letters.
• s is between "A" and "FXSHRXW".

Solution in python:

class Solution:
    def titleToNumber(self, s: str) -> int:
        base = 1
        result = 0
        for i in range(len(s)-1, -1, -1):
            result += base * (ord(s[i]) - 64)
            base *= 26
        return result