Leetcode 171 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 

Solution 1: simple math problem.

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