class Solution {
public:
 bool isSymmetric(TreeNode* root) {
 queue<struct TreeNode*>q;
 q.push(root);
 while(!q.empty()){
 int size = q.size();
 vector<struct TreeNode*>vec;
 while(size--){
 struct TreeNode* cnt = q.front();
 q.pop();
 if(cnt->left) q.push(cnt->left);
 if(cnt->right) q.push(cnt->right);
 vec.push_back(cnt->left);
 vec.push_back(cnt->right);
 }
 int i=0, j=vec.size()-1;
 while(i<j){
 if(vec[i]!=NULL && vec[j]!=NULL){
 if(vec[i]->val != vec[j]->val) return false;
 }
 else if(vec[i] != vec[j]) return false; 
 i++;
 j--;
 }
 }
 return true;
 }
};