leetcode NO.637 二叉树的层平均值

层序遍历二叉树时顺便求出每一层的和即可

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