[leetcode-637-Average of Levels in Binary Tree]

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].

思路：

层次遍历。

vector<double> averageOfLevels(TreeNode* root)
{
  vector<double>ret;
        if(root==NULL)return ret;
    queue<TreeNode*>que;
    que.push(root);
    TreeNode* temp;
    while(!que.empty())
    {
      int n = que.size(); 
      double sum = 0;
      for(int i = 0;i<n;i++)
      {
        temp = que.front();
        que.pop();
        sum+= temp->val;
        if(temp->left!=NULL)que.push(temp->left);
        if(temp->right!=NULL)que.push(temp->right);
      }
      ret.push_back(sum/(double)n);      
    }
    return ret;
}