Excel Sheet Column Number

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.

class Solution {
public:
    int titleToNumber(string s) {
        if(s=="") return 0;
        int ans = 0;
        for(int i = 0;i < s.size();i++)
        {
            ans = ans*26 + s[i]-'A'+1;
        }
        
        return ans;
    }
};