using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{ 

    public static void Main()

    {

        var ids = new List<int> {1,2,3,4,5,5,6};

        Dist(ids);

        foreach (var id in ids)

        {

            Console.WriteLine(id);

        }

    }

    public static void Dist(ICollection<int> list)

    {

        list = list.Distinct().ToArray();

    }

}