[LeetCode] 101. Symmetric Tree

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题目内容

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:

    1
   / \
  2   2
 / \ / \
3  4 4  3
But the following [1,2,2,null,3,null,3] is not:
    1
   / \
  2   2
   \   \
   3    3

给定一个二叉树，检查它是否是镜像对称的。

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题目思路

这道题目挺简单的...就是运用递归来比较两个对称的节点。如果都不存在说明TRUE，如果有一个不存在有一个存在说明FALSE，如果数值相等继续向下比较，否则也是FALSE

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程序代码

# 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 or (not root.right and not root.left):
            return True
        return self.check(root.left,root.right)
    
    def check(self,left,right):
        if not left and not right:
            return True
        if (not left and right) or (not right and left):
            return False
        if left.val==right.val:
            return self.check(left.left,right.right) and self.check(left.right,right.left)
        else:
            return False