Leetcode 199: Binary Tree Right Side View

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

For example:
Given the following binary tree,

   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---

 

You should return [1, 3, 4].

 

/**
 * 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<int> RightSideView(TreeNode root) {
        var queue = new Queue<TreeNode>();
        var result = new List<int>();
        
        if (root == null) return result;
        
        queue.Enqueue(root);
        
        int count = 1;
        while (queue.Count > 0)
        {
            for (int i = 0; i < count; i++)
            {
                var n = queue.Dequeue();
                if (n.left != null) queue.Enqueue(n.left);
                if (n.right != null) queue.Enqueue(n.right);
                
                if (i == count - 1) result.Add(n.val);
            }
            
            count = queue.Count;
        }
        
        return result;
    }
}