# 637.Average of Levels in Binary Tree

**637.Average of Levels in Binary Tree**

难度:Easy

> 给定一个非空二叉树, 返回一个由每层节点平均值组成的数组.

```
示例 1:

输入:
    3
   / \
  9  20
    /  \
   15   7
输出: [3, 14.5, 11]
解释:
第0层的平均值是 3,  第1层是 14.5, 第2层是 11. 因此返回 [3, 14.5, 11].
注意：

节点值的范围在32位有符号整数范围内。
```

分层遍历可以使用基本的队列存储，

```
/**
 * 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>res;
        if(!root) return res;
        deque<TreeNode*> tree(1,root);
        while(!tree.empty())
        {
            double sum=0.0;
            int len=tree.size();
            int k=len;
            while(k--)
            {
                sum+=tree[0]->val;
                if(tree[0]->left) tree.push_back(tree[0]->left);
                if(tree[0]->right) tree.push_back(tree[0]->right);
                tree.pop_front();
            }
            res.push_back(sum/len);
            
        }
        return res;
        
    }
};
```


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