leetcode 637. 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.

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