171、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

int titleToNumber(string s) {
        //这题太简单了，不多说了
        int len = s.size();
        int num = 0;
        for (int i = 0; i < len; ++i)
            num = num * 26 + s[i] - 'A' + 1;
        return num;
    }