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 
    ...

Example 1:

Input: "A"
Output: 1

Example 2:

Input: "AB"
Output: 28

Example 3:

Input: "ZY"
Output: 701

Constraints:

1 <= s.length <= 7
s consists only of uppercase English letters.
s is between "A" and "FXSHRXW".

Solution:

class Solution {
    public int titleToNumber(String s) {
        int val = 0;
        for (int i = s.length() - 1; i >= 0; i --) {
            char c = s.charAt(i);
            val += (c - 'A' + 1) * Math.pow(26, s.length() - 1 - i);
        }
        return val;
    }
}