168. Excel Sheet Column Title

Given a positive integer, return its corresponding column title as appear in an Excel sheet.

For example:

    1 -> A
    2 -> B
    3 -> C
    ...
    26 -> Z
    27 -> AA
    28 -> AB 
题目含义：给定一个int数，返回其代表的字符串，规则如上

    public String convertToTitle(int n) {
         String result = "";
        while (n > 0) {
            result = (char) ('A' + (n - 1) % 26) + result;
            n = (n - 1) / 26;
        }
        return result;       
    }