Excel Sheet Column Number -- leetcode

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 

class Solution {
public:
    int titleToNumber(string s) {
        int ans = 0;
        for (auto ch : s) {
            ans = ans * 26 + ch - 'A' + 1;
        }
        return ans;
    }
};