leetcode 序列化二叉树

https://leetcode-cn.com/problems/xu-lie-hua-er-cha-shu-lcof/

就是层级遍历，搞一个queue，然后层级遍历，左右子树为空也要add到queue，因为要保留整颗树的结构，反解析的时候同理，遇到为null的，就不添加queue了

import java.util.LinkedList;
import java.util.Queue;

public class Codec {
    public String serialize(TreeNode root) {
        if(root == null) {
            return "[]" ;
        }

        StringBuilder stringBuilder = new StringBuilder();
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.add(root);
        stringBuilder.append("[");
        while (!queue.isEmpty()){
            TreeNode node = queue.poll();
            if(node != null) {
                stringBuilder.append(node.val);
                stringBuilder.append(",");
                queue.add(node.left);
                queue.add(node.right);
            } else {
                stringBuilder.append("null,");
            }
        }

        stringBuilder.deleteCharAt(stringBuilder.length()-1);
        stringBuilder.append("]");

        return stringBuilder.toString();
    }

    public TreeNode deserialize(String data) {
        if(data.equals("[]")) {
            return null;
        }

        String nodeStr = data.substring(1, data.length()-1);
        String[] nodeVal = nodeStr.split(",");
        TreeNode root = new TreeNode(Integer.parseInt(nodeVal[0]));
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.add(root);
        int index = 1;
        while (!queue.isEmpty()){
            TreeNode node = queue.poll();
            if(!nodeVal[index].equals("null")){
                node.left = new TreeNode(Integer.parseInt(nodeVal[index]));
                queue.add(node.left);
            }

            index++;

            if(!nodeVal[index].equals("null")){
                node.right = new TreeNode(Integer.parseInt(nodeVal[index]));
                queue.add(node.right);
            }

            index++;
        }

        return root;
    }
}