using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        HashSet<Question> qh = new HashSet<Question>();

        qh.Add(new Question()

        {ID = "1"});

        qh.Add(new Question()

        {ID = "1"});

        qh.Add(new Question()

        {ID = "2"});

        for (int i = 0; i < qh.Count(); i++)

        {

            Console.WriteLine(qh.ElementAt(i).ID);

        }

    }

​

    public class Question

    {

        public string ID

        {

            get;

            set;

        }

​

        public override int GetHashCode()

        {

            return ID.GetHashCode();

        }

​

        public override bool Equals(System.Object obj)

        {

            return (obj != null && obj.GetType() == typeof (Question)) ? (this.ID == ((Question)(obj)).ID) : false;

            ;

        }

    }

}