LeetCode 297. Serialize and Deserialize Binary Tree

Description

https://leetcode.com/problems/serialize-and-deserialize-binary-tree/

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.

Explanation

use bfs to serialize and deserialize

Python Solution

# 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
        """
        results = ""
        
        if not root:
            return results
        
        queue = []
        queue.append(root)
        
        while queue:
            size = len(queue)
            
            for i in range(0, size):
                node = queue.pop(0)

                if not node:
                    results += "None,"
                else:
                    results += str(node.val) + ","            

                    queue.append(node.left)
                    queue.append(node.right)    

        return results
        
    def deserialize(self, data):
        """Decodes your encoded data to tree.
        
        :type data: str
        :rtype: TreeNode
        """
        if not data:
            return None
        
        values = data.split(',')
        
        root = TreeNode(int(values[0]))
        
        queue = []
        queue.append(root)
        
        i = 1
        while queue and i < len(values):
            node = queue.pop(0)
            
            if values[i] != "None":
                left = TreeNode(int(values[i]))
                node.left = left
                queue.append(left)
            i += 1        

            if values[i] != "None":
                right = TreeNode(int(values[i]))
                node.right = right
                queue.append(right)
            i += 1
                        
        return root

# Your Codec object will be instantiated and called as such:
# ser = Codec()
# deser = Codec()
# ans = deser.deserialize(ser.serialize(root))
  • Time complexity: ~N
  • Space complexity: ~N

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