## Description

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,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.

## Explanation

use bfs to serialize and deserialize

## Python Solution

```
# 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
"""
results = ""
if not root:
return results
queue = []
queue.append(root)
while queue:
size = len(queue)
for i in range(0, size):
node = queue.pop(0)
if not node:
results += "None,"
else:
results += str(node.val) + ","
queue.append(node.left)
queue.append(node.right)
return results
def deserialize(self, data):
"""Decodes your encoded data to tree.
:type data: str
:rtype: TreeNode
"""
if not data:
return None
values = data.split(',')
root = TreeNode(int(values[0]))
queue = []
queue.append(root)
i = 1
while queue and i < len(values):
node = queue.pop(0)
if values[i] != "None":
left = TreeNode(int(values[i]))
node.left = left
queue.append(left)
i += 1
if values[i] != "None":
right = TreeNode(int(values[i]))
node.right = right
queue.append(right)
i += 1
return root
# Your Codec object will be instantiated and called as such:
# ser = Codec()
# deser = Codec()
# ans = deser.deserialize(ser.serialize(root))
```

- Time complexity: ~N
- Space complexity: ~N

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