Java判断是不是完全二叉树

boolean isCompleteTree(TreeNode root){
        if(root == null) return true;
        Queue queue = new LinkedList<>();
        queue.offer(root);
        TreeNode cur = queue.poll();
        while(cur != null) {
            queue.offer(cur.left);
            queue.offer(cur.right);
            cur = queue.poll();
        }
        while (!queue.isEmpty()){
            if(queue.peek() != null){
                return false;
            }
            queue.poll();
        }
        return false;
    }