Serialize and Deserialize Binary Tree.md

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.

My code:

# 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 serialize(self, root):
        """Encodes a tree to a single string.
        
        :type root: TreeNode
        :rtype: str
        """
        if root==None:
            return []
        record=[]
        check_list=[root]
        count_num=0
        while check_list:
            count_num+=1
            root=check_list[0]
            if len(check_list)>1:
                check_list=check_list[1:]
            else:
                check_list=[]
            if root!=None:
                record.append(root.val)
            else:
                record.append(-999)
            if root:
                check_list.append(root.left)    
                check_list.append(root.right)
        #print(count_num)
        #print(record)
        return record 
    def deserialize(self, data):
        """Decodes your encoded data to tree.
        
        :type data: str
        :rtype: TreeNode
        """
        if len(data)==0:
            return None
        root0=TreeNode(data[0])
        i=1
        check_list=[root0]
        while i<len(data):
            root=check_list[0]
            if len(check_list)>1:
                check_list=check_list[1:]
            else:
                check_list=[]
            if data[i]!=-999:
                left=TreeNode(data[i])
            else:
                left=None
                
            i=i+1
            root.left=left
            if left!=None:
                check_list.append(left)
            if i<len(data):
                if data[i]!=-999:
                    right=TreeNode(data[i])
                else:
                    right=None
                i=i+1
                root.right=right
                if right!=None:
                    check_list.append(right)
        return root0
                
        

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

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