using System;

using System.Linq;

​

public class Program

{

    public class MemberInformation

    {

        public long PrimaryIdentity;

        public long DependentIdentity;

    }

​

    public static MemberInformation[] information = new MemberInformation[]{new MemberInformation{PrimaryIdentity = 1, DependentIdentity = 2}, new MemberInformation{PrimaryIdentity = 1, DependentIdentity = 3}, new MemberInformation{PrimaryIdentity = 1, DependentIdentity = 4}, new MemberInformation{PrimaryIdentity = 5, DependentIdentity = 6}, };

    public static void Main()

    {

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(1)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(2)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(3)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(4)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(5)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(6)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(1, true)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(2, false)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(3, false)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(4, false)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(5, true)));

        Console.WriteLine("Identities {0}", string.Join(", ", GetIdentities(6, false)));

    }

​

    public static long[] GetIdentities(long identity)

    {

        long[] results = new long[]{0};

        var defaultIdentity = information.FirstOrDefault(x => x.DependentIdentity == identity);

        long primary = defaultIdentity != null ? defaultIdentity.PrimaryIdentity : identity;

        results = information.Where(x => x.PrimaryIdentity == primary).Select(x => x.DependentIdentity).Union(new long[]{primary}).Distinct().ToArray();

        return results;

    }

​

    public static long[] GetIdentities(long identity, bool isPrimary)

    {

        long[] results = new long[]{0};

        if (isPrimary)

        {

            results = information.Where(x => x.PrimaryIdentity == identity).Select(x => x.DependentIdentity).Union(new long[]{identity}).Distinct().ToArray();

        }

        else

        {

            results = information.Where(y => y.PrimaryIdentity == information.First(x => x.DependentIdentity == identity).PrimaryIdentity).Select(x => x.DependentIdentity).Union(new long[]{information.First(x => x.DependentIdentity == identity).PrimaryIdentity}).Distinct().ToArray();

        }

​

        return results;

    }

}