428. Serialize and Deserialize N-ary Tree

/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> children;

    public Node() {}

    public Node(int _val,List<Node> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Codec {

    // Encodes a tree to a single string.
    public String serialize(Node root) {
        if (root == null) {
            return "";
        }
        StringBuilder sb = new StringBuilder();
        serializeHelper(root, sb);
        return sb.toString();
    }
    
    private void serializeHelper(Node root, StringBuilder sb) {
        if (root == null) {
            sb.append("0").append(",");
            return;
        }
        List<Node> children = root.children;
        sb.append(root.val).append(",").append(children.size()).append(",");
        for (Node child : children) {
            serializeHelper(child, sb);
        }
    }

    // Decodes your encoded data to tree.
    public Node deserialize(String data) {
        if (data.equals("")) {
            return null;
        }
        Deque<String> queue = new LinkedList<>(Arrays.asList(data.split(",")));
        return deserializeHelper(queue);
    }
    
    private Node deserializeHelper(Deque<String> queue) {
        if (queue.isEmpty()) {
            return null;
        }
        int val = Integer.parseInt(queue.pollFirst());
        int size = Integer.parseInt(queue.pollFirst());
        Node root = new Node(val, new ArrayList<>());
        for (int i = 0; i < size; i++) {
            root.children.add(deserializeHelper(queue));
        }
        return root;
    }
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));