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

class Solution {
    public String convertToTitle(int n) {

        StringBuilder sb = new StringBuilder();
        while (n > 0){
            n--;
            sb.append((char)('A' + n % 26));
            n /= 26;
        }

        return sb.reverse().toString();
    }
}