【剑指Offer】37. 序列化二叉树

import java.util.*;
import java.lang.*;
/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    String Serialize(TreeNode root) {
        if(root == null) return "[]";
        // 序列化[1,2,3,null,4,5]
        StringBuilder res = new StringBuilder("[");
        Queue<TreeNode> q = new LinkedList<>();
        q.add(root);
        while(!q.isEmpty()) {
            TreeNode node = q.poll();
            if(node != null) { 
                res.append(node.val+",");
                q.add(node.left);
                q.add(node.right);
            }else {
                res.append("null,");
            }
        }
        res.append("]");
        return res.toString();
  }
    TreeNode Deserialize(String str) {
       if(str.equals("[]")) return null;
        
        String[] sarr = str.substring(1,str.length()-1).split(",");
        Queue<TreeNode> q = new LinkedList<>();
        TreeNode root = new TreeNode(Integer.parseInt(sarr[0]));
        q.add(root);
        int i = 1;
        while(!q.isEmpty()) {
            TreeNode node = q.poll();
            if(!sarr[i].equals("null")) {
                node.left = new TreeNode(Integer.parseInt(sarr[i]));
                q.add(node.left);
            }
            i++;
            if(!sarr[i].equals("null")) {
                node.right = new TreeNode(Integer.parseInt(sarr[i]));
                q.add(node.right);
            }
            i++;   
        }
        return root;
  }
}