Solution.py

# 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 root is None:
            return ''
        res = []

        def preorder(root):
            if root is None:
                res.append("#,")
                return
            res.append(str(root.val) + ",")
            preorder(root.left)
            preorder(root.right)

        preorder(root)
        return ''.join(res)

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

        :type data: str
        :rtype: TreeNode
        """
        if not data:
            return None
        vals = data.split(',')

        def inner():
            first = vals.pop(0)
            if first == '#':
                return None
            return TreeNode(int(first), inner(), inner())

        return inner()


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