public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if(root==null) return "";
        Queue<TreeNode> queue=new LinkedList<>();
        StringBuilder res=new StringBuilder();
        queue.offer(root);
        while(!queue.isEmpty()){
            TreeNode cur=queue.poll();
            if(cur==null){
                res.append("n ");
                continue;
            }
            res.append(cur.val+" ");
            queue.offer(cur.left);
            queue.offer(cur.right);
        }
        return res.toString();
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if(data=="") return null;
        Queue<TreeNode> queue=new LinkedList<>();
        String[] values=data.split(" ");
        TreeNode root=new TreeNode(Integer.parseInt(values[0]));
        queue.offer(root);
        for(int i=1;i<values.length;i++){
            TreeNode cur=queue.poll();
            if(!values[i].equals("n")){
                TreeNode left=new TreeNode(Integer.parseInt(values[i]));
                cur.left=left;
                queue.offer(left);
            }
            if (!values[++i].equals("n")) {
                TreeNode right = new TreeNode(Integer.parseInt(values[i]));
                cur.right = right;
                queue.add(right);
            }
        }
        return root;
    }
}