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

[分析]
26进制转10进制

[注意事项]
1）s == null的处理

[Code]

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

reference: http://www.danielbit.com/blog/puzzle/leetcode/leetcode-excel-sheet-column-number