leetcode-637：二叉树的层平均值

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] 。

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def averageOfLevels(self, root: TreeNode) -> List[float]:
        if not root:
            return []
        queue = [root]
        res = []
        while queue:
            l = len(queue)
            tmp = []
            for _ in range(l):
                cur =  queue.pop(0)
                tmp.append(cur.val)
                left,right = cur.left,cur.right
                if left:
                    queue.append(left)
                if right:
                    queue.append(right)
            res.append(sum(tmp)/len(tmp))  ## 新增的地方
        return res

class Solution {
public:
    vector<double> averageOfLevels(TreeNode* root) {
        if(!root) return {};
        vector<double> res;
        queue<TreeNode*> queue;
        queue.push(root);
        while(!queue.empty()){
            int l=queue.size();
            double tmp=0;
            for(int i=0;i<l;i++){
                TreeNode* cur=queue.front();
                queue.pop();
                tmp+=cur->val;
                if(cur->left){
                    queue.push(cur->left);
                }
                if(cur->right){
                    queue.push(cur->right);
                }
            }
            tmp/=l;
            res.push_back(tmp);
        }
        return res;
    }
};