Is Serialize and Deserialize Binary Tree easy or hard?

Serialize and Deserialize Binary Tree is classified as a Hard problem on LeetCode. The difficulty comes from designing a reversible encoding scheme that preserves the full tree structure, including null children.

Serialize and Deserialize Binary Tree Python/Java solution

Python and Java implementations typically use preorder traversal with a delimiter-separated string and a null marker such as '#'. Deserialization reads tokens sequentially and recursively reconstructs the tree. Both languages achieve O(n) time and O(n) space complexity.

How to solve Serialize and Deserialize Binary Tree in O(n)?

Traverse the tree using preorder DFS and record values in a string while inserting a special marker like # for null nodes. During reconstruction, read the sequence sequentially and recursively build left and right children. Each node and placeholder is processed once, resulting in O(n) time.

What is the best approach for Serialize and Deserialize Binary Tree?

Preorder depth-first traversal with null markers is the most common solution. The tree is serialized by visiting nodes in preorder and writing a placeholder for missing children. During deserialization, the same order allows recursive reconstruction of the exact structure in O(n) time.

Is Serialize and Deserialize Binary Tree asked at Google/Amazon/Meta?

Serialize and Deserialize Binary Tree frequently appears in interviews at companies like Google, Amazon, Meta, and Microsoft. The problem tests tree traversal, recursion design, and the ability to encode and reconstruct data structures.

What data structure is used in Serialize and Deserialize Binary Tree?

The main data structures include binary trees, recursion stacks, queues for BFS solutions, and strings or arrays to store serialized values. DFS solutions rely on recursive calls, while BFS implementations use a queue for level-order traversal.

What is the time complexity of Serialize and Deserialize Binary Tree?

Both serialization and deserialization run in O(n) time where n is the number of nodes in the tree. Each node is processed exactly once, and null placeholders are handled in constant time operations.

Description Solution Video 13:48

297. Serialize and Deserialize Binary Tree

Hard61.1% acceptance23 companies

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.

Clarification: The input/output 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.

Example 1:

Input: root = [1,2,3,null,null,4,5]
Output: [1,2,3,null,null,4,5]

Example 2:

Input: root = []
Output: []

Constraints:

The number of nodes in the tree is in the range [0, 10⁴].
-1000 <= Node.val <= 1000

Asked at top 20 of 23 companies

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Topics

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Similar problems

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LanguageLoading editor…

1# Definition for a binary tree node.
2# class TreeNode(object):
3#     def __init__(self, x):
4#         self.val = x
5#         self.left = None
6#         self.right = None
7 
8class Codec:
9 
10    def serialize(self, root):
11        """Encodes a tree to a single string.
12        
13        :type root: TreeNode
14        :rtype: str
15        """
16        
17 
18    def deserialize(self, data):
19        """Decodes your encoded data to tree.
20        
21        :type data: str
22        :rtype: TreeNode
23        """
24        
25 
26# Your Codec object will be instantiated and called as such:
27# ser = Codec()
28# deser = Codec()
29# ans = deser.deserialize(ser.serialize(root))

Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

[1,2,3,null,null,4,5]

Input

[]

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