Python – Serialize & Deserialize Binary Tree (BFS Level‑Order) – Interview DSA Solution 🚀

This solution tackles the Serialize and Deserialize Binary Tree problem using a BFS level‑order traversal approach. The goal is to convert a binary tree into a string representation and rebuild it, preserving its structure.

Key Concepts:

BFS Level‑Order Traversal:
We use a queue to traverse the tree level by level, ensuring that nodes are processed in the order they appear.

Null Markers:
The marker "#" is used to represent null nodes, ensuring that the structure (including missing children) is maintained.

Step‑by‑Step Explanation:

TreeNode Definition:
Similar to the DFS solution, we define a basic TreeNode class.

class TreeNode:
def __init__(self, val=0, left=None, right=None):

#TreeNode #DataStructure

Serialization (BFS):
The serialize method uses a deque to perform level‑order traversal. Each node's value is added to the result list; if a node is null, "#" is appended. The final list is joined into a string.

def serialize(self, root):
if not root:
return ""
q = deque([root])
result = []
while q:
if node:
else:
return ' '.join(result)

#BFS #LevelOrder #Serialization

Deserialization (BFS):
The deserialize method reconstructs the tree from the serialized string. It uses a deque to assign left and right children for each node in a level‑order manner.

def deserialize(self, data):
if not data:
return None
root = TreeNode(int(values[0]))
q = deque([root])
i = 1
while q:
if values[i] != '#':
i += 1
if values[i] != '#':
i += 1
return root

#BFS #TreeReconstruction #Deserialization

Real‑World Applications:
The BFS approach is useful for encoding trees in a way that preserves their structure exactly, which is critical in network transmissions, file storage, and system design.

Code:

# BFS Level‑Order Approach for Serialize & Deserialize Binary Tree
from collections import deque

class TreeNode:
def __init__(self, val=0, left=None, right=None):

class CodecBFS:
def serialize(self, root):
if not root:
return ""
q = deque([root])
result = []
while q:
if node:
else:
return ' '.join(result)

def deserialize(self, data):
if not data:
return None
root = TreeNode(int(values[0]))
q = deque([root])
i = 1
while q:
if values[i] != '#':
i += 1
if values[i] != '#':
i += 1
return root

# Example usage:
if __name__ == "__main__":
# Constructing a sample tree:
# 1
# / \
# 2 3
# / \
# 4 5
root = TreeNode(1, TreeNode(2), TreeNode(3, TreeNode(4), TreeNode(5)))
codec_bfs = CodecBFS()
print("BFS Serialized:", serialized_bfs)
# (Traverse deserialized_root_bfs to verify correctness)

#SerializeDeserialize #BinaryTree #BFS #LevelOrder #CodingInterview #PythonDSA