/**
 * 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 {
  bool isMirror(TreeNode *t1, TreeNode *t2) {
    if (t1 == NULL && t2 == NULL) return true;
    if (t1 == NULL || t2 == NULL) return false;
    return (t1->val == t2->val) && isMirror(t1->right, t2->left) &&
           isMirror(t1->left, t2->right);
  }

 public:
  bool isSymmetric(TreeNode *root) { return isMirror(root, root); }
};