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 
题目含义：给定一串字符，求解对应的数字

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