Solutions CS101

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101.对称二叉树 ​

https://leetcode.cn/problems/symmetric-tree/

给你一个二叉树的根节点 root ， 检查它是否轴对称。

示例 1：

img
输入：root = [1,2,2,3,4,4,3]
输出：true

示例 2：

img
输入：root = [1,2,2,null,3,null,3]
输出：false

提示：

  • 树中节点数目在范围 [1, 1000] 内
  • -100 <= Node.val <= 100
python
# 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:
        if not root:
            return True

        def isMirror(left: TreeNode, right: TreeNode) -> bool:
            if not left and not right:
                return True
            if not left or not right:
                return False
            return (left.val == right.val) and isMirror(left.left, right.right) and isMirror(left.right, right.left)

        return isMirror(root.left, root.right)