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.
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.
# 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)) 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)