对称二叉树
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def isSymmetric(self, root: TreeNode) -> bool:
def is_mirrow(a, b):
if a is None and b is None: return True
if a is None or b is None: return False
if a.val != b.val: return False
return is_mirrow(a.left, b.right) and is_mirrow(a.right, b.left)
if not root: return True
return is_mirrow(root.left, root.right)