Description
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.
Solutions
1. BFS
# Time: O(n)
# Space: O(n)
# 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
"""
if not root:
return ''
queue = collections.deque()
queue.append(root)
res = []
while queue:
node = queue.popleft()
if not node:
res.append('null')
continue
res.append(str(node.val))
queue.append(node.left)
queue.append(node.right)
return ','.join(res)
def deserialize(self, data):
"""Decodes your encoded data to tree.
:type data: str
:rtype: TreeNode
"""
if not data:
return None
nodes = data.split(',')
n = len(nodes)
queue = collections.deque()
root = TreeNode(int(nodes[0]))
queue.append(root)
i = 1
while i < n:
parent = queue.popleft()
if nodes[i] != 'null':
left = TreeNode(int(nodes[i]))
parent.left = left
queue.append(left)
i += 1
if nodes[i] != 'null':
right = TreeNode(int(nodes[i]))
parent.right = right
queue.append(right)
i += 1
return root
# Your Codec object will be instantiated and called as such:
# codec = Codec()
# codec.deserialize(codec.serialize(root))
# 48/48 cases passed (116 ms)
# Your runtime beats 56.73 % of python3 submissions
# Your memory usage beats 100 % of python3 submissions (17.7 MB)