python 代码

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if not root:#为空对称
            return True
        if root.left and not root.right or root.right and not root.left:#根节点左右存在一个不在就不对称
            return False
        if not root.left and root.right:#只有根节点对称
            return True
        tree=root.left
        subtree=self.turn(root.right)
        if self.isMatch(tree,subtree):#左子树和右子树镜面匹配则对称
            return True
        return False

    def turn(self,subtree):#右子树的镜面
        if not subtree:
            return None
        subtree.left,subtree.right=subtree.right,subtree.left
        self.turn(subtree.left)
        self.turn(subtree.right)
        return subtree

    def isMatch(self,A,B):#判断是否匹配
        if not A and not B:
            return True
        if not A and B or not B and A:
            return False
        if A and B and A.val!=B.val:
            return False
        return self.isMatch(A.left,B.left) and self.isMatch(A.right,B.right)