Python3解leetcode Symmetric Tree

最新推荐文章于 2025-08-04 16:58:05 发布

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最新推荐文章于 2025-08-04 16:58:05 发布

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文章标签： python

原文链接：http://www.cnblogs.com/xiaohua92/p/11067956.html

博客提出判断二叉树是否为自身镜像（即围绕中心对称）的问题，给出示例说明对称与不对称的情况，还提到若能用递归和迭代两种方法解决可加分，思路是考虑用递归解法解决该二叉树问题。

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问题描述：

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

But the following [1,2,2,null,3,null,3] is not:

Note:
Bonus points if you could solve it both recursively and iteratively.

思路：二分类树的问题，可以考虑递归解法

# 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:
        if root == None:
            return True
        def ismirror(root1,root2):
            if root1 == None and root2 ==None:
                return True
            elif root1 == None or root2 ==None or root1.val != root2.val:
                return False
            return ismirror(root1.left,root2.right) and ismirror(root1.right,root2.left) 
        
        return ismirror(root.left,root.right)