题目：

题解：

class Solution:
    # 在【100. 相同的树】的基础上稍加改动
    def isSameTree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
        if p is None or q is None:
            return p is q
        return p.val == q.val and self.isSameTree(p.left, q.right) and self.isSameTree(p.right, q.left)

    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        return self.isSameTree(root.left, root.right)