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.

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

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Codec:
    def __init__(self):
        self.serialized_array = []
        self.index = 0

    def serialize(self, root):
        """Encodes a tree to a single string.

        :type root: TreeNode
        :rtype: str
        """
        self.serialization_help(root)
        return self.serialized_array


    def serialization_help(self, root):
        if root == None:
            self.serialized_array.append(None)
            return 
        self.serialized_array.append(root.val)
        self.serialize(root.left)
        self.serialize(root.right)

    def deserialize(self, data):
        """Decodes your encoded data to tree.

        :type data: str
        :rtype: TreeNode
        """
        if self.index == len(data) or data[self.index] == None:
            self.index += 1
            return None

        root = TreeNode(data[self.index])
        self.index += 1
        root.left = self.deserialize(data)
        root.right = self.deserialize(data)
        return root


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