Problem :

My 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
def preorder(root, tree):
if root:
preorder(root.left, tree)
preorder(root.right, tree)

tree = []
preorder(root, tree)
return ','.join(map(str, tree))

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

:type data: str
:rtype: TreeNode
def build(data):
val = data.pop()
if val == 'N':
node = TreeNode(int(val))
node.left = build(data)
node.right = build(data)
return node

data = data.split(',')
data = data[::-1]
return build(data)