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 

public class Solution {
    public int titleToNumber(String s) {
        int x  = 0;
        if(s==null || s.length()==0) {
            return x;
        }
        for(int i=0;i<s.length();i++) {
            x *= 26;
            x += s.charAt(i) - 'A' + 1;
        }
        return x;
    }
}