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

S: math 26进制

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