/**
 * 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 check(TreeNode *p, TreeNode *q){
        if (p == nullptr && q == nullptr){
            return true;
        } else if (p == nullptr || q == nullptr){
            return false;
        } 
        return p->val == q->val && check(q->left, p->right) && check(q->right, p->left);
    }
    bool isSymmetric(TreeNode* root) {
        return check (root,root);
    }
};