Leetcode: Excel Sheet Column Number

Question

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 

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

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Analysis

it is an easy math problem.

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Solution

class Solution:
    # @param {string} s
    # @return {integer}
    def titleToNumber(self, s):
        res = 0
        if s=="":
            return res

        s = list(s)
        n = len(s)
        for i in range(len(s)):
            res += (ord(s[i])-64) * (26**(n-1-i))

        return res