leetcode 297. Serialize and Deserialize Binary Tree

Posted 2021-02-11 jamieliu

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 a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.

Example: 

You may serialize the following tree:

    1
   /   2   3
     /     4   5

as "[1,2,3,null,null,4,5]"

Clarification: The above format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.

Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

 

 

每次遇到递归就容易想不出来。。

还有就是一些基本的API：

StringBuilder -- 将Integer or String加入用的是append

string可以用split() 来进行拆分，括号里面写拆分依据，比如(",")

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {
    
    private static String spliter = ",";
    private static String NN = "X";

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        StringBuilder sb = new StringBuilder();
        buildString(root, sb);
        return sb.toString();
    }
    public void buildString(TreeNode node, StringBuilder sb) {
        if(node == null){
            sb.append(NN).append(spliter); 
        } else {
            sb.append(node.val).append(spliter);
            buildString(node.left, sb);
            buildString(node.right, sb);
        }
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        Deque<String> nodes = new LinkedList<>();
        nodes.addAll(Arrays.asList(data.split(spliter)));
        return buildTree(nodes);
    }
    public TreeNode buildTree(Deque<String> nodes){
        String v = nodes.remove();
        if(v.equals(NN)){
            return null;
        }else {
            TreeNode node = new TreeNode(Integer.valueOf(v));
            node.left = buildTree(nodes);
            node.right = buildTree(nodes);
            return node;
        }
        
    }
}

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