void mixLists(
LinkedList<Integer> left,
LinkedList<Integer> right,
ArrayList<LinkedList<Integer>> mix,
LinkedList<Integer> before) {
if (before.isEmpty() || right.isEmpty()) {
LinkedList<Integer> l = new LinkedList<>();
l = (LinkedList<Integer>) before.clone();
l.addAll(left);
l.addAll(right);
mix.add(l);
return;
}
int hl = left.removeFirst();
before.addLast(hl);
mixLists(left, right, mix, before);
before.removeLast();
left.addFirst(hl);
int hr = right.removeFirst();
before.addLast(hr);
mixLists(left, right, mix, before);
before.removeLast();
right.addFirst(hr);
}
ArrayList<LinkedList<Integer>> bstSequences(TN nd) {
ArrayList<LinkedList<Integer>> seq = new ArrayList<>();
if (nd == null) {
seq.add(new LinkedList<Integer>());
return seq;
}
LinkedList<Integer> before = new LinkedList<>();
before.add(nd.val);
ArrayList<LinkedList<Integer>> left_seq = bstSequences(nd.left);
ArrayList<LinkedList<Integer>> right_seq = bstSequences(nd.right);
for (LinkedList<Integer> left : left_seq) {
for (LinkedList<Integer> right : right_seq) {
ArrayList<LinkedList<Integer>> mix = new ArrayList<>();
mixLists(left, right, mix, before);
seq.addAll(mix);
}
}
return seq;
}