[Algo] Rotate String

Rotate String by n place. Lower Case keeps lower, upper keep upper

e.g. abc, 2 -> cde

abAB 2 -> cdCD 

public String rotate(String str, int n) {
    char[] charArr = str.toCharArray();
    for (int i = 0; i < charArr.length; i++) {
        if (!Character.isLetter(charArr[i])) {
            continue;
        }
            char base = Character.isUpperCase(charArr[i]) ? 'A' : 'a';
            charArr[i] = (char)(base +  ((charArr[i] - base + n) % 26));
        }
        return new String(charArr);
}