text: /**
   * 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 {
  public:
      vector<double> averageOfLevels(TreeNode* root) {
          vector<double> ans;
          
          if(!root)
              return ans;
          
          queue<TreeNode*> q;
          q.push(root);
          
          double avg;
          long long int sum = root -> val;
          
          while(!q.empty()){
              int size = q.size();
              
              avg = (double)sum / size;
              ans.push_back(avg);
              
              sum = 0;
              
              for(int i = 0; i < size; i++){
                  auto x = q.front();
                  q.pop();
                  if(x -> left){
                      q.push(x ->left);
                      sum += x -> left -> val;
                  }
                  if(x -> right){
                      q.push(x -> right);
                      sum += x -> right -> val;
                  }
              }
          }
          return ans;
      }
  };