from typing import Optional


# 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 root is None:
            return True
        return self.isMirrorTree(root.left, root.right)

    def isMirrorTree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
        if p is None or q is None:
            if p is None and q is None:
                return True
            return False
        if p.val != q.val:
            return False
        if p.left and q.right:
            if not self.isMirrorTree(p.left, q.right):
                return False
        elif p.left or q.right:
            return False

        if p.right and q.left:
            if not self.isMirrorTree(p.right, q.left):
                return False
        elif p.right or q.left:
            return False
        return True