public boolean isRotation(String s1, String s2){
        if(s1.length()!=s2.length()){
            return false;
        }
        s1 = s1+s1;
        for(int i=0; i<s1.length()/2; i++){
            if(s1.substring(i, s2.length()+i).equals(s2)){
                return true;
            }
        }
        return false;
    }