算法：二叉树的层序遍历算法分享

public List levelOrder(TreeNode root) {
		List list = new ArrayList<>();
		Queue queue = new LinkedList<>();
		
		TreeNode node = root;
		queue.offer(node);
		while(!queue.isEmpty()) {
			node = queue.poll();
			list.add(node.val);
			if (node.left != null) {
				queue.offer(node.left);
			}
			if (node.right != null) {
				queue.offer(node.right);
			}
		}
		
		return list;
    }