【每日一题Leetcode】101Symmetric Tree

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本文介绍了一种检查二叉树是否为中心对称的方法，通过递归比对左右子树来实现。提供了Python代码示例，并附带了一个示例二叉树用于说明。

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：可以利用上次的题对比两个树是否相同的思路。

# 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):
        """
        :type root: TreeNode
        :rtype: bool
        """
        
        #check if root is None.
        if root == None:
            return True
        else:       
            return self.isMirror(root.left,root.right)        
       
        
    def isMirror(self,left,right):
        
        if left and right:   
            if left.val != right.val:
                return False
            else:
                return (self.isMirror(left.left,right.right)) & (self.isMirror(left.right,right.left))
            
        elif left != right:
            return False
            
        return True

参考：https://leetcode.com/problems/symmetric-tree/discuss/33050/Recursively-and-iteratively-solution-in-Python