using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public class TreeNode 

    {

      public int val;

      public TreeNode left;

      public TreeNode right;

      public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) 

      {

          this.val = val;

          this.left = left;

          this.right = right;

      }

  }

    public static bool IsCompleteTree(TreeNode root) {

        if (root == null)

            return true;

​

        var queue = new Queue<TreeNode>();

        queue.Enqueue(root);

​

        while (queue.Peek() != null)

        {

            var node = queue.Dequeue();

            queue.Enqueue(node.left);

            queue.Enqueue(node.right);

        }

​

        while (queue.Any() && queue.Peek() == null)

        {

            queue.Dequeue();

        }

        return !queue.Any();

    }

    public static void Main()

    {

        Console.WriteLine("UniLecs");

        // tests

        var root = new TreeNode(1);

        root.left = new TreeNode(2);

        root.right = new TreeNode(3);

        root.left.left = new TreeNode(4);

        root.left.right = new TreeNode(5);

        root.right.left = new TreeNode(6);

        Console.WriteLine(IsCompleteTree(root)); // true

        var root2 = new TreeNode(1);

        root2.left = new TreeNode(2);

        root2.right = new TreeNode(3);

        root2.left.left = new TreeNode(4);

        root2.left.right = new TreeNode(5);

        root2.right.right = new TreeNode(7);

        Console.WriteLine(IsCompleteTree(root2)); // false

    }

}