class Solution {
    public List<List<Integer>> printFromTopToBottom(TreeNode root) {
        List<List<Integer>> ras = new ArrayList<>();
        if(root==null) return ras;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        boolean flag = true;
        while(!queue.isEmpty()){
            int size = queue.size();
            List<Integer> curList = new LinkedList<>();
            for(int i=0;i<size;i++){
                TreeNode node = queue.poll();
                if(flag) curList.add(node.val);
                else curList.add(0,node.val);

                if(node.left!=null) queue.add(node.left);
                if(node.right!=null) queue.add(node.right);
            }
            flag = !flag;
            ras.add(curList);
        }
        return ras;
    }
}