Level-order Traversal

1void levelOrder(Node root) {2  Queue<Node> q = new LinkedList<>(); q.add(root);  // Start queue with the root3  while (!q.isEmpty()) {  // Until the queue drains4    Node node = q.poll();  // Take the front node5    out.add(node.val);  // Visit this node6    if (node.left != null) q.add(node.left);  // Enqueue left child7    if (node.right != null) q.add(node.right);  // Enqueue right child8  }9}