Leetcode637.Average of Levels in Binary Tree二叉树的层平均值

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.

class Solution {
public:
    vector<double> averageOfLevels(TreeNode* root) {
        vector<double> res;
        if(root == NULL)
            return res;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty())
        {
            int len = q.size();
            double sum = 0;
            for(int i = 0; i < len; i++)
            {
                TreeNode *node = q.front();
                q.pop();
                sum += node ->val;
                if(node ->left != NULL)
                    q.push(node ->left);

                if(node ->right != NULL)
                    q.push(node ->right);
            }
            res.push_back(sum / len);
        }
        return res;
    }
};