/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode() : val(0), left(nullptr), right(nullptr) {} * TreeNode(int x) : val(x), left(nullptr), right(nullptr) {} * TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {} * }; */ class Solution { public: bool isSymmetric(TreeNode* root) { return isSymmetric(root, root); } private: bool isSymmetric(TreeNode* p, TreeNode* q) { if (!p || !q) return p == q; return p->val == q->val && isSymmetric(p->left, q->right) && isSymmetric(p->right, q->left); } };