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要说序列化和反序列化，得先从 JSON 数据格式说起。 JSON 的运用非常广泛，比如我们经常将变成语言中的结构体序列化成JSON 字符串，存入缓存或者通过网络发送给远端服务，消费者接受JSON 字符串然后进行反序列化，就可以得到原始数据了。 这就是序列化和反序列化的目的，以某种特定格式组织数据，使得数据可以独立于编程语言。 那么假设现在有一棵用 Java 实现的二叉树，我想把它通过某些方式存储下来，然后用 C++ 读取这棵并还原这棵二叉树的结构，怎么办？这就需要对二叉树进行序列化和反序列化了。

前言

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一、力扣297. 二叉树的序列化与反序列化

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode(int x) { val = x; }* }*/
public class Codec {String SEP = ",";String NULL = "#";// Encodes a tree to a single string.public String serialize(TreeNode root) {StringBuilder sb = new StringBuilder();serialize(root,sb);return sb.toString();}// Decodes your encoded data to tree.public TreeNode deserialize(String data) {LinkedList<String> list = new LinkedList<>();for(String s : data.split(SEP)){list.add(s);}return fun(list); }public TreeNode fun(LinkedList<String> list){if(list.isEmpty()){return null;}String first = list.removeFirst();if(first.equals(NULL)){return null;}TreeNode cur = new TreeNode(Integer.parseInt(first));cur.left = fun(list);cur.right = fun(list);return cur;}public void serialize(TreeNode root, StringBuilder sb){if(root == null){sb.append(NULL).append(SEP);return;}sb.append(root.val).append(SEP);serialize(root.left,sb);serialize(root.right,sb);}
}// Your Codec object will be instantiated and called as such:
// Codec ser = new Codec();
// Codec deser = new Codec();
// TreeNode ans = deser.deserialize(ser.serialize(root));

二、力扣二叉树后序序列化

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode(int x) { val = x; }* }*/
public class Codec {// Encodes a tree to a single string.public String serialize(TreeNode root) {if(root == null){return "#";}String l = serialize(root.left);String r = serialize(root.right);return l + "," + r + "," + root.val;}// Decodes your encoded data to tree.public TreeNode deserialize(String data) {LinkedList<String> list = new LinkedList<>();for(String s : data.split(",")){list.add(s);}return fun(list);}public TreeNode fun(LinkedList<String> list){String last = list.removeLast();if(last.equals("#")){return null;}TreeNode cur = new TreeNode(Integer.parseInt(last));cur.right = fun(list);cur.left = fun(list);return cur;}
}// Your Codec object will be instantiated and called as such:
// Codec ser = new Codec();
// Codec deser = new Codec();
// TreeNode ans = deser.deserialize(ser.serialize(root));

三、力扣二叉树层序序列化与反序列化

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode(int x) { val = x; }* }*/
public class Codec {// Encodes a tree to a single string.public String serialize(TreeNode root) {if(root == null){return "";}StringBuilder sb = new StringBuilder();Deque<TreeNode> deq = new LinkedList<>();deq.offerLast(root);while(!deq.isEmpty()){int len = deq.size();for(int i = 0; i < len; i ++){TreeNode cur = deq.pollFirst();if(cur == null){sb.append("#").append(",");continue;}sb.append(cur.val).append(",");deq.offerLast(cur.left);deq.offerLast(cur.right);}}return sb.toString();}// Decodes your encoded data to tree.public TreeNode deserialize(String data) {if(data.isEmpty()){return null;}String[] da = data.split(",");TreeNode root = new TreeNode(Integer.parseInt(da[0]));Deque<TreeNode> deq = new ArrayDeque<>();int index = 0;deq.offerLast(root);while(!deq.isEmpty()){int len = deq.size();for(int i = 0; i < len; i ++){TreeNode cur = deq.pollFirst();index ++;if(!da[index].equals("#")){cur.left = new TreeNode(Integer.parseInt(da[index]));deq.offerLast(cur.left);}index ++;if(!da[index].equals("#")){cur.right = new TreeNode(Integer.parseInt(da[index]));deq.offerLast(cur.right);}}}return root;}
}// Your Codec object will be instantiated and called as such:
// Codec ser = new Codec();
// Codec deser = new Codec();
// TreeNode ans = deser.deserialize(ser.serialize(root));