Excel Sheet Column Number leetcode

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 res = 0;
        for (int i = 0; i < s.length(); i++) {
            int tem = (int) (s.charAt(i) - 'A') + 1;
            res = res * 26 + tem;
        }
        return res;
    }
}