נתונות פעולות רקורסיביות mystery ו-secret:

public static int mystery(String s1, String s2)
{
    if (s1.length() == 0 && s2.length() == 0) return 0;
    if (s1.length() == 0) return -1;
    if (s2.length() == 0) return 1;
    if (s1.charAt(0) < s2.charAt(0)) return -1;
    if (s1.charAt(0) > s2.charAt(0)) return 1;
    return mystery(s1.substring(1), s2.substring(1));
}

public static String[] secret(String[] arr, String s)
{
    String[] temp = new String[arr.length];
    secretHelp(arr, temp, s, 0, 0, temp.length - 1);
    return temp;
}

private static void secretHelp(String[] arr, String[] temp, String s, int i, int left, int right)
{
    if (i < arr.length)
    {
        if (mystery(arr[i], s) < 0)
        {
            temp[left] = arr[i];
            secretHelp(arr, temp, s, i + 1, left + 1, right);
        }
        else
        {
            temp[right] = arr[i];
            secretHelp(arr, temp, s, i + 1, left, right - 1);
        }
    }
}