637

637. Average of Levels in Binary Tree (Easy)

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.

Companies:
Amazon, Facebook

Related Topics:
Tree

Similar Questions:

• Binary Tree Level Order Traversal (Medium)
• Binary Tree Level Order Traversal II (Easy)

Solution 1. Level-order Traversal

// OJ: https://leetcode.com/problems/average-of-levels-in-binary-tree/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
public:
    vector<double> averageOfLevels(TreeNode* root) {
        if (!root) return {};
        vector<double> ans;
        queue<TreeNode*> q;
        q.push(root);
        while (q.size()) {
            double cnt = q.size(), sum = 0;
            for (int i = 0; i < cnt; ++i) {
                root = q.front();
                q.pop();
                sum += root->val;
                if (root->left) q.push(root->left);
                if (root->right) q.push(root->right);
            }
            ans.push_back(sum / cnt);
        }
        return ans;
    }
};