# # 【LeetCode】297. Serialize and Deserialize Binary Tree 解题报告（Python）

## # 题目描述：

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.

## # 解题方法

449. Serialize and Deserialize BSTopen in new window多么的像呀！之前我说，只知道前序遍历是没法确定一个树的，我说的不严谨。如果前序遍历的过程中记录下哪些位置是空节点的话，就是可以确定这棵树的。LeetCode的官方树的构建就是这样的。

``````# 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
"""
vals = []
def preOrder(root):
if not root:
vals.append('#')
else:
vals.append(str(root.val))
preOrder(root.left)
preOrder(root.right)
preOrder(root)
return ' '.join(vals)

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

:type data: str
:rtype: TreeNode
"""
vals = collections.deque(val for val in data.split())
def build():
if vals:
val = vals.popleft()
if val == '#':
return None
root = TreeNode(int(val))
root.left = build()
root.right = build()
return root
return build()

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

## # 日期

2018 年 3 月 15 日 --雾霾消散，春光明媚