Excel Sheet Column Number

Description：

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 

Code：

 int titleToNumber(string s) {
        int result = 0;
        for (int i = 0; i < s.size(); i++)
        {
            result+=(s[i]-'A'+1)*(int)(pow((double)26,s.size()-i-1));
        }
        return result;
    }