LeetCode Excel Sheet Column Title 168

1 -> A
2 -> B
3 -> C
...
26 -> Z
27 -> AA
28 -> AB

public String convertToTitle(int n) {
	String str = "";
	do {
		int chrInt = n % 26;
		char chr;
		if (chrInt == 0) {
			chr = 'Z';
			n -= 26;
		} else {
			chr = (char) (chrInt - 1 + 'A');
		}
		str = chr + str;
		n = n / 26;
	} while (n != 0);
	return str;
}

public String convertToTitle(int n) {
    if(n <= 0){
        throw new IllegalArgumentException("Input is not valid!");
    }

    StringBuilder sb = new StringBuilder();

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

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