637. Average of Levels in Binary Tree

Here is my discussion post.

The algorithm can be solved using BFS algorithm, level by level can be implemented to track nodes in the queue first; same level nodes will be visited one by one using a while loop by tracking count of nodes.

Here are highlights:

1. Learn the technique to apply BFS using Queue, and track level by level by tracking nodes in the queue;
2. For each level, calculate sum of each node's value; data type of sum should be long not int, and then average value will be double, so it is better to declare as double type;
3. I completed the solution using 13 minutes.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public IList<double> AverageOfLevels(TreeNode root)
        {
            var averages = new List<double>();

            if (root == null)
                return averages;

            var queue = new Queue<TreeNode>();
            queue.Enqueue(root); 

            // push into queue by level 
            while(queue.Count > 0)
            {
                var count = queue.Count;
                double sum = 0; 
                for(int i = 0; i < count; i++)
                {
                    var current = queue.Dequeue();
                    sum += current.val;

                    if (current.left != null)
                        queue.Enqueue(current.left);

                    if (current.right != null)
                        queue.Enqueue(current.right); 
                }

                averages.Add(sum/count);
            }

            return averages;
        }
}