171. Excel Sheet Column Number

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:

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