using System;

using System.Collections.Generic;

using System.Linq;

using System.Collections;

​

public class Program

{

    public static void Main()

    {

        //Intersect

        var listA = new List<string>{"A", "B", "C", "D", "G"};

        var listB = new List<string>{"C", "C", "A", "E", "A", "F", "Q", "Q"};

        var matching = listA.Intersect(listB).ToList();

        Console.WriteLine(matching.Str());

        //Right Inner Join

        var query = listA.GroupJoin(listB, a => a, b => b, (a, abList) => abList.ToList());

        Console.WriteLine(query.Str());

        //Inner Distinct

        var innerDist = listA.Union(listB);

        Console.WriteLine(innerDist.Str());

        //Outter Distinct

        var flippedDupMatch = listB.Union(listA).Except(listB.Intersect(listA));

        Console.WriteLine(flippedDupMatch.Str());

    }

}

​

public static class Temp

{

    public static string Str(this IEnumerable<string> str)

    {

        return str.Count() + " " + string.Join(",", str);

    }

​

    public static string Str(this List<string> str)

    {

        return str.Count() + " " + string.Join(",", str);

    }

​

    public static string Str(this IEnumerable<List<string>> str)

    {

        return str.SelectMany(x => x).ToList().Str();

    }

}