428. Serialize and Deserialize N-ary Tree

Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.

Design an algorithm to serialize and deserialize an N-ary tree. An N-ary tree is a rooted tree in which each node has no more than N children. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that an N-ary tree can be serialized to a string and this string can be deserialized to the original tree structure.

For example, you may serialize the following 3-ary tree

as [1 [3[5 6] 2 4]]. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.

Note:

N is in the range of [1, 1000]
Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

Solution

(1) Java

/*
// 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) {
        return helper1(root);
    }

    private String helper1(Node root) {
        if (root == null) {
            return "";
        }
        String rst = ""+root.val+",";
        List<Node> children = root.children;
        rst += children.size();
        for (Node child : children) {
            rst += ","+ helper1(child);
        }
        return rst;
    }

    // Decodes your encoded data to tree.
    public Node deserialize(String data) {
        if (data == null || data.length() == 0) {
            return null;
        }
        String[] nodes = data.split(",");      
        Deque<String> q = new LinkedList<String>(Arrays.asList(nodes));
        return helper2(q);        
    }

    private Node helper2(Deque<String> q) {
        Node node = new Node();
        node.val = Integer.parseInt(q.poll());
        int size = Integer.parseInt(q.poll());
        node.children = new ArrayList<Node>(size);
        for (int i = 0; i < size; i++) {
            node.children.add(helper2(q));
        }
        return node;
    }
}

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

428. Serialize and Deserialize N-ary Tree