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.

//Can the input be empty?
//Can the result overflow 32bits integer?
//All the letters are given in capital?

class Solution {
public:
    int titleToNumber(string s) {
        int re = 0;
        //parse from left to right
        for(size_t i = 0; i < s.size(); i++){
            re = re * 26 + s[i] - 'A' + 1;
        }
        return re;
    }
};