image2

public Iterable<Key> keys() {return keys(min(), max());}
public Iterable<Key> keys(Key lo, Key hi) {
    Queue<Key> queue = new Queue<Key>();
    keys(root, queue, lo, hi);
    return queue;
}
private void keys(Node x, Queue<Key> queue, Key lo, Key hi) {
    if(x == null) return;
    int cmplo = lo.compareTo(x.key);
    int cmphi = hi,compareTo(x.key);
    if(cmplo < 0) keys(x.left, queue, lo, hi);
    if(cmplo <= 0 && cmphi >= 0) queue.enqueue(x.key);
    if(cmphi >0) keys(x.right, queue, lo, hi);
}