Greatest Common Divisor of Strings.java

class Solution {
    public String gcdOfStrings(String str1, String str2) {
       if (!(str1 + str2).equals(str2 + str1)) {
            return "";
        }
        int gcdLength = gcd(str1.length(), str2.length());
        return str1.substring(0, gcdLength);
    }
    
    public int gcd(int x, int y) {
            if (y == 0) {
                return x;
            } else {
                return gcd(y, x % y);
            }    
    } 
}