using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var treeList = Enumerable.Repeat(0, 100).ToList();

        var rnd = new Random();

        for (int n = 1; n < 101 ; n++)

        {

          var i = rnd.Next(100);    

          while (treeList[i] != 0)

          {

              i = (i + 1) % 100;

          }

          treeList[i] = n;

        }

        for (var i = 0; i < 100; i++)

        {

            if (i % 20 == 0 && i != 0)

            {

                Console.WriteLine();

                Console.WriteLine("                    ---------- ");

                Console.WriteLine();            

            }

            Console.Write(treeList[i] + "  ");

​

        }

    }

}