二叉树层序遍历

//层序遍历
    public void levelOrder(TreeNode root) {
        if(root == null) {
            return;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            TreeNode cur = queue.poll();
            System.out.print(cur.val+" ");
            if(cur.left != null) {
                queue.offer(cur.left);
            }
            if(cur.right != null) {
                queue.offer(cur.right);
            }
        }
    }