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;
    }
};
*/
/*
Serialize function
Time Complexity: O(M * K) = O(M * 11) = O(M)
Space Complexity: O(M * K) = O(M * 11) = O(M)
M = Number of Nodes
K = Average Length of each node. (Bounded by 11)

Deserialize function
Time Complexity: O(N + M + M*K) = O(N + M*K) = O(N+N) = O(N)
Space Complexity: O(M * K) = O(N)
N = Length of the input string
M = Number of Nodes
K = Average Length of each node. (Bounded by 11)
*/
class Codec {

    // Encodes a tree to a single string.
    public String serialize(Node root) {
        List<String> list = new ArrayList();
        if (root == null) {
            return "";
        }
        serializeHelper(list, root);
        return String.join(",", list);
    }

    private void serializeHelper(List<String> list, Node node) {
        if (node == null) {
            return;
        }
        list.add(String.valueOf(node.val));
        list.add(String.valueOf(node.children.size()));
        for (Node child : node.children) {
            serializeHelper(list, child);
        }
    }

    // Decodes your encoded data to tree.
    public Node deserialize(String data) {
        if (data == null || data.length() == 0) {
            return null;
        }
        return deserializeHelper(new LinkedList<String>(Arrays.asList(data.split(","))));
    }

    private Node deserializeHelper(Queue<String> queue) {
        if (queue == null || queue.isEmpty()) {
            return null;
        }
        Node node = new Node();
        node.val = Integer.parseInt(queue.poll());
        int noOfChildren = 0;
        if (!queue.isEmpty()) {
            noOfChildren = Integer.parseInt(queue.poll());
        }
        node.children = new ArrayList<Node>(noOfChildren);
        for (int i = 0; i < noOfChildren; i++) {
            node.children.add(deserializeHelper(queue));
        }
        return node;
    }
}

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