# LeetCode 297. Serialize and Deserialize Binary Tree

## 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))

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