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    // Level-Order Traversal
    public List<List<Integer>> levelOrder(Node root) {
        List<List<Integer>> result = new ArrayList<>();
        if (root == null) return result;

        Queue<Node> queue = new LinkedList<>();
        queue.offer(root);

        while (!queue.isEmpty()) {
            int size = queue.size();
            List<Integer> currentLevel = new ArrayList<>();
            for (int i = 0; i < size; i++) {
                Node currentNode = queue.poll();
                currentLevel.add(currentNode.val);
                for (Node child : currentNode.children) {
                    queue.offer(child);
                }
            }
            result.add(currentLevel);
        }

        return result;
    }
}