[LeetCode] 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].

Note:

1. The range of node's value is in the range of 32-bit signed integer.

题目要求一个非空二叉树的每一层数字和的平均值，并返回一个数组。首先想到的是二叉树的层次遍历，将每一层放去queue的数取平均值即可，需要注意的是int -> double的转换。

class Solution {
public:
    vector<double> averageOfLevels(TreeNode* root) {
        vector<double> res;
        double avg = 0;
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty()) {
            int n = q.size();
            double sum = 0;
            for (int i = 0; i != n; i++) {
                TreeNode* node = q.front();
                q.pop();
                sum += node->val;
                if (node->left != nullptr)
                    q.push(node->left);
                if (node->right != nullptr)
                    q.push(node->right);
            }
            avg = sum / n;
            res.push_back(avg);
        }
        return res;
    }
};
// 16 ms