serializeTree.py

# """
# 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.
#
# For example, you may serialize the following tree
#
#     1
#    / \
#   2   3
#      / \
#     4   5
#
# as "[1,2,3,null,null,4,5]", just the same as how LeetCode OJ 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.
# """

# 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
        """
        def flat(root):
            if not root:
                return ['null']
            return [root.val] + flat(root.left) + flat(root.right)

        return '['+','.join(map(str,flat(root)))+']'

    def deserialize(self, data):
        """Decodes your encoded data to tree.

        :type data: str
        :rtype: TreeNode
        """
        def construct(s):
            if not s:   return []
            n = s.pop(0)
            if n!= 'null':
                node = TreeNode(n)
                node.left, s = construct(s)
                node.right, s = construct(s)
            else:
                node = None
            return node, s
        return construct(data[1:-1].split(','))[0]



# Your Codec object will be instantiated and called as such:
# codec = Codec()
# codec.deserialize(codec.serialize(root))