/
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
/
class Solution {
public:
bool check(TreeNode l,TreeNode* r){
if(!l&&!r) return true;
if(!l||!r||l->val!=r->val) return false;

    return check(l->left,r->right)&&check(l->right,r->left);
}

bool isSymmetric(TreeNode* root) {
    return root==nullptr||check(root->left,root->right);
}

};