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 -> 1B -> 2C -> 3...Z -> 26AA -> 27AB -> 28 

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