428. Serialize and Deserialize N-ary Tree

// Idea: preorder recursive traversal; add number of children after root val, in order to know when to terminate.
// Example: The example in description is serialized as: "1,3,3,2,5,0,6,0,2,0,4,0"

class Codec {

    // Encodes a tree to a single string.
    public String serialize(Node root) {
        List<String> list=new LinkedList<>();
        serializeHelper(root,list);
        return String.join(",",list);
    }
    
    private void serializeHelper(Node root, List<String> list){
        if(root==null){
            return;
        }else{
            list.add(String.valueOf(root.val));
            list.add(String.valueOf(root.children.size()));
            for(Node child:root.children){
                serializeHelper(child,list);
            }
        }
    }

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

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.

428. Serialize and Deserialize N-ary Tree

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