637. Average of Levels in Binary Tree（LeetCode）

Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

Example 1:

Input:
    3
   / 
  9  20
    /  
   15   7
Output: [3, 14.5, 11]
Explanation:
The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].

Note:

1. The range of node's value is in the range of 32-bit signed integer.

   /**
    * 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:
       vector<double> averageOfLevels(TreeNode* root) {
            vector<double> vet;
            if (root == NULL)
                return vet;
            stack<TreeNode*> stacknode;
            stacknode.push(root);
            while (stacknode.size())
            {
                double sum = 0;
                int count = stacknode.size();
                stack<TreeNode*> stacknode1 = stacknode;
                while (stacknode.size())
                {
                    TreeNode* pNode = stacknode.top();
                    sum += pNode->val;
                    stacknode.pop();
                }
                vet.push_back(sum / count);
                while (stacknode1.size())
                {
                    TreeNode* pNode1 = stacknode1.top();
                    if (pNode1->right)
                        stacknode.push(pNode1->right);
                    if (pNode1->left)
                        stacknode.push(pNode1->left);
                    stacknode1.pop();
                }
               
            }
            return vet;
       }
   };