Excel Sheet Column Number （LeetCode Math)

Question:  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

Idea: Actually it is a special 26cimal (may be a wrong word?) to decimal problem, e.g. AB-> ('A'- 'A'+1 )*26 + ('B' - 'A'+1) -> 28. The 26cimal is denoted as 1,2,...,26, algebraically the same as using 0,1,...,9 to denote decimal.

Time: O(n) Space: O(1)

Code:

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