1. Pythonic写法；
2. 支持正负数，浮点数；
3. no 递归 no递归 no递归；
4. 序列化&反序列化代码非常对称；
5. 采用AcWing序列化二叉树的方式；

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None


from collections import deque

class Solution:
    def serialize(self, root):
        """Encodes a tree to a single string.

        :type root: TreeNode
        :rtype: str
        """
        if not root: return '[]'
        res = []
        q = deque()
        q.append(root)
        while q:
            x = q.popleft()
            if x:
                res.append(x.val)
                q.append(x.left)
                q.append(x.right)
            else:
                res.append(None)
        return str(res)

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

        :type data: str
        :rtype: TreeNode
        """
        arr = eval(data)
        if not arr: return None
        q = deque()
        rt = TreeNode(arr[0])
        q.append(rt)
        i = 1
        while q:
            x = q.popleft()
            if arr[i] is not None:
                x.left = TreeNode(arr[i])
                q.append(x.left)
            if arr[i + 1] is not None:
                x.right = TreeNode(arr[i + 1])
                q.append(x.right)
            i += 2
        return rt