LeetCode-637. Average of Levels in Binary TreeLevel up your coding skills and quickly land a job. This is the best place to expand your knowledge and get prepared for your next interview.https://leetcode.com/problems/average-of-levels-in-binary-tree/Given the root of a binary tree, return the average value of the nodes on each level in the form of an array. Answers within 10-5 of the actual answer will be accepted.

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: [3.00000,14.50000,11.00000]
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].

Example 2:

Input: root = [3,9,20,15,7]
Output: [3.00000,14.50000,11.00000]

Constraints:

• The number of nodes in the tree is in the range [1, 10^4].
• -2^31 <= Node.val <= 2^31 - 1

【C++】

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<double> averageOfLevels(TreeNode* root) {
        vector<double> res;
        if (root == nullptr) {return res;}
        queue q;
        q.push(root);
        while (!q.empty()) {
            int size = q.size(), count = size;
            double sum = 0;
            while (size-- > 0) {
                TreeNode* node = q.front();
                q.pop();
                sum += node->val;
                if (node->left) {q.push(node->left);}
                if (node->right) {q.push(node->right);}
            }
            res.push_back(sum / count);
        }
        return res;
    }
};

【Java】

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List averageOfLevels(TreeNode root) {
        List res = new ArrayList<>();
        if (root == null) {return res;}
        Queue q = new LinkedList<>();
        q.offer(root);
        while (!q.isEmpty()) {
            int size = q.size(), count = size;
            double sum = 0;
            while (size-- > 0) {
                TreeNode node = q.poll();
                sum += node.val;
                if (node.left != null) {q.offer(node.left);}
                if (node.right != null) {q.offer(node.right);}
            }
            res.add(sum / count);
        }
        return res;
    }
}