* Definition for a binary tree node.
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
bool check(TreeNode* left , TreeNode* right)
if(!left && !right)return true;
else if( !left || !right) return false;
if(left->val != right->val) return false;
return check(left->right, right->left) && check(left->left, right->right);
bool isSymmetric(TreeNode* root) {
if(!root->left && !root->right) return true;
return check(root->left, root->right);