# 297. Serialize and Deserialize Binary Tree

Reference: LeetCode
Difficulty: Hard

## Problem

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:

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.

## Analysis

### BFS

Note:

• Check the null case.
• Handle , in the string. Remove it in the end.
• Use StringBuffer.
• Compatible with null nodes.

Time: $O(N)$ if using StringBuffer for string concatenation.
Space: $O(N)$ since we need to keep the entire tree.

Serialize:

Deserialize:

• Handle the base cases.
• Before the while loop, handle the root node first. So you don’t need an extra dummy node.

### DFS (Solution)

• We don’t need to remove the last ,. The return list after split does not include "".
• If root is null, the string is null.

Time: $O(N)$ if using StringBuffer for string concatenation.
Space: $O(N)$ since we need to keep the entire tree.

Serialize:

Deserialize:

• In rdeserialize, null check for L is not necessary. We assume the input is a valid preorder input.

Comment
Junhao Wang
a software engineering cat