1 class Solution {

 2 public:

 3     vector<double>ans;

 4     vector<double> averageOfLevels(TreeNode* root) {

 5         if(!root) return ans;

 6         queue<TreeNode*>q;

 7         q.push(root);

 8         while(!q.empty()){

 9             int num = q.size();double sum = 0;

10             for(int i = 0;i < num;i++){

11                 TreeNode* node = q.front();q.pop();

12                 sum += node->val;

13                 if(node->left!=NULL) q.push(node->left);

14                 if(node->right!=NULL) q.push(node->right);

15             }

16             ans.push_back(sum/num);

17         }

18         return ans;

19     }

20 };