Excel Sheet Column Title

public class Solution {    public String convertToTitle(int n) {        if (n <= 0) {            return null;        }        StringBuilder sb = new StringBuilder();        while (n > 0) {            n--;            char c = (char) (n % 26 + 'A');            n = n / 26;            sb.append(c);        }        sb.reverse();        return sb.toString();    }}