題目：請實現一個函式，用來判斷一顆二叉樹是不是對稱的。注意，如果一個二叉樹同此二叉樹的映象是同樣的，定義其為對稱的。

牛客網：連結

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    def Symmetrical(self, left, right):
        if not left and not right:
            return True
        if left and right:
            return left.val == right.val and self.Symmetrical(left.left, right.right) and self.Symmetrical(left.right, right.left)
    def isSymmetrical(self, pRoot):
        # write code here
        if not pRoot:
            return True
        return self.Symmetrical(pRoot.left, pRoot.right)