class Solution {
    public List<Integer> printFromTopToBottom(TreeNode root) {
        List<Integer> arr= new ArrayList<Integer>();
        if(root==null)
            return arr;

        Queue<TreeNode> q=new LinkedList<TreeNode>();
        q.add(root);

        while(!q.isEmpty())
        {
            TreeNode node=q.poll();
            arr.add(node.val);
            if(node.left!=null)
                q.add(node.left);
            if(node.right!=null)
                q.add(node.right);
        }
        return arr;
    }
}