637. Average of Levels in Binary Tree

637. Average of Levels in Binary Tree

Question

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].

Thinking:

• Method 1:BFS

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<Double> averageOfLevels(TreeNode root) {
        List<Double> result = new ArrayList<>();
        if(root == null) return result;
        LinkedList<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while(!queue.isEmpty()){
            int len = queue.size();
            double sum = 0D;
            for(int i = 0; i < len; i++){
                TreeNode temp = queue.poll();
                sum += temp.val;
                if(temp.left != null) queue.add(temp.left);
                if(temp.right != null) queue.add(temp.right);
            }
            result.add(sum / len);
        }
        return result;
    }
}