public class test
{
    public static void main(String[] args)
    {
        String s1 = "GATC";
        System.out.println(s1);

        String s2 = shuffle(s1);
        System.out.println(s2);
    }

    public static String shuffle(String str)
    {
        if(str.length() <= 1)
            return str;

        String tmp1 = shuffle(str.substring(0, (str.length()/2)));
        String tmp2 = shuffle(str.substring(str.length()/2));

        if(Math.random() > 0.5)
            return tmp1 + tmp2;
        else
            return tmp2 + tmp1;
    }
}