Excel Sheet Column Number(java)

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 n = s.length();         int sum = 0;         for(int i=0 ; i<n ;i++)         {             sum += (s.charAt(n-i-1)-'A'+1) * Math.pow(26, i) ;         }return sum;    }}