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) {
        char[] ch_list=s.toCharArray();
        int size=ch_list.length;
        int sum=0;
        for(int i=0;i<size;i++){
            int num=ch_list[i]-'A'+1;
            sum=sum+(int)Math.pow(26,size-i-1)*num;
        }
        return sum;
    }
}