428. Serialize and Deserialize N-ary Tree

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:

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

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跟serialize bst⼀个思路路。注意每个点后面都要加”,” example: 1,#,3,2,4,#,5,6,#,#,#,#,#,

/*
// 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 "";
        
        Queue<Node> que = new LinkedList<>();
        StringBuilder sb = new StringBuilder();
        sb.append(Integer.toString(root.val)).append(",#,");
        que.add(root);
        
        while (!que.isEmpty()) {
            Node node = que.poll();
            for (Node n : node.children) {
                sb.append(Integer.toString(n.val)).append(",");
                que.add(n);
            }
            sb.append("#,");
        }
        
        return sb.toString();
    }

    // Decodes your encoded data to tree.
    public Node deserialize(String data) {
        if (data.length() == 0) return null;
        String[] s = data.split(",");

        Queue<Node> que = new LinkedList<>();
        Node root = new Node(Integer.parseInt(s[0]), new ArrayList<Node>());
        que.add(root);
        int i = 1;
        
        while (!que.isEmpty()) {
            Node node = que.poll();
            i++;
            while (!s[i].equals("#")) {
                Node c = new Node(Integer.parseInt(s[i]), new ArrayList<>());
                node.children.add(c);
                que.add(c);
                i++;
            }
        }
        
        return root;
    }
}

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