101. 对称二叉树

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# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isSymmetric(self, root: Optional[TreeNode]) -> bool: 
        # print(root.left.val,root.right.val)
        def Symmetric(a,b):
            if (a and b and a.val != b.val) or (a and b==None) or (a==None and b) :
                return False
            if (a==None and b==None):
                return True  
            if (a.val==b.val):
                result1 = Symmetric(a.left,b.right)
                result2 = Symmetric(a.right,b.left)
                if result1 != False and result2 != False:
                    return True 
                else:
                    return False
        return Symmetric(root.left,root.right)