using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

        public static bool ExistsNonSelectedElement(int[] arr, List<int> selectedElements)

        {

            if(selectedElements == null || arr == null) 

            {

                return false;

            }

            bool resultFlag = arr.OrderBy(e => e).Any(e => !selectedElements.Distinct().OrderBy(e => e).Contains(e));

            return resultFlag;

        }

​

        public static int GetRandomElement(int[] arr)

        {

            int element = 0;

            var randomIndex = new Random().Next(minValue: 0, maxValue: arr.Length);

            element = arr[randomIndex];

            return element;

        }

​

        public static void Main()

        {

            int[] givenArr = new Int32[] { 1, -3, 0, -3, 1, 0, 0, 0, 2, 1 };

            List<int> selectedElements = new List<int>();

            while(ExistsNonSelectedElement(arr: givenArr, selectedElements: selectedElements))

            {

                var elem = GetRandomElement(givenArr);

                if(!selectedElements.Contains(elem))

                {

                    selectedElements.Add(elem);

                }

            }

​

            Console.WriteLine($"Selected elements: [{string.Join( separator: ", ", selectedElements)}]");

        }

}