297.Serialize and Deserialize Binary Tree

Posted 2020-09-18 panini

题目：

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.

For example, you may serialize the following tree

    1
   / \\
  2   3
     / \\
    4   5

as "[1,2,3,null,null,4,5]", just the same as how LeetCode OJ 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.

链接： http://leetcode.com/problems/serialize-and-deserialize-binary-tree/

5/14/2017

算法班，deserialize部分抄的

层序遍历的方法

注意

1. 第36行需要减去最后一个","

2. 第44行将string里面的各个char转为数字和#

3. deserialize部分，TreeNode部分来自于queue，新建的子树node值来自于values

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Codec {
11     private final String nullNode = "#";
12     private final String delimiter = ",";
13     
14     // Encodes a tree to a single string.
15     public String serialize(TreeNode root) {
16         StringBuilder sb = new StringBuilder();
17         if (root == null) return "#";
18 
19         Queue<TreeNode> queue = new LinkedList<TreeNode>();
20         sb.append("[");
21         queue.offer(root);
22         while (!queue.isEmpty()) {
23             int size = queue.size();
24             for (int i = 0; i < size; i++) {
25                 TreeNode node = queue.poll();
26                 if (node == null) {
27                     sb.append(nullNode);
28                 } else {
29                     sb.append(node.val);
30                     queue.offer(node.left);
31                     queue.offer(node.right);
32                 }
33                 sb.append(delimiter);
34             }
35         }
36         sb.deleteCharAt(sb.length() - 1);
37         sb.append("]");
38         return sb.toString();
39     }
40 
41     // Decodes your encoded data to tree.
42     public TreeNode deserialize(String data) {
43         if (data.equals("#")) return null;
44         String[] values = data.substring(1, data.length() - 1).split(delimiter);
45         Queue<TreeNode> queue = new LinkedList<TreeNode>();
46         TreeNode root = new TreeNode(Integer.parseInt(values[0]));
47         
48         queue.offer(root);
49         for (int i = 1; i < values.length; i++) {
50             // node comes from queue, left/right comes from values
51             TreeNode parent = queue.poll();
52             if (!values[i].equals(nullNode)) {
53                 TreeNode left = new TreeNode(Integer.parseInt(values[i]));
54                 parent.left = left;
55                 queue.add(left);
56             }
57             i++;
58             if (!values[i].equals(nullNode)) {
59                 TreeNode right = new TreeNode(Integer.parseInt(values[i]));
60                 parent.right = right;
61                 queue.add(right);
62             }
63         }
64         return root;
65     }
66 }
67 
68 // Your Codec object will be instantiated and called as such:
69 // Codec codec = new Codec();
70 // codec.deserialize(codec.serialize(root));

也可以递归调用

http://www.cnblogs.com/yrbbest/p/5047035.html

别人的答案

https://discuss.leetcode.com/topic/30195/recursive-dfs-iterative-dfs-and-bfs

更多讨论

https://discuss.leetcode.com/category/375/serialize-and-deserialize-binary-tree