leetcode-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 

public class Solution {
    public int titleToNumber(String s) {
        int sum=0;
        char []ch=s.toCharArray();
        for(int i=0;i<ch.length;i++)
        {
        	sum=26*sum+(ch[i]-'A'+1); 
        }
        return sum;
    }
}