Leetcode 297. Serialize and Deserialize Binary Tree

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

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,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.

• 序列化和解析二叉树。
• https://leetcode.com/problems/serialize-and-deserialize-binary-tree/discuss/74259/Recursive-preorder-Python-and-C%2B%2B-O(n)
• Built-in Functions — Python 3.7.4 documentation
  • https://docs.python.org/3/library/functions.html?highlight=iter#iter
  • https://docs.python.org/3/library/functions.html#next
  • https://docs.python.org/3.7/library/stdtypes.html#str.split