using System;

using System.Collections.Generic;

using System.Linq;

​

using Newtonsoft.Json;

​

namespace DataAccess

{

    public class Program

    {

        public static void Main()

        {

            var sequenceA = new[] { "a", "a", "b", "b", "c" };

            var sequenceB = new[] { "a", "a", "a", "b", "c", "c", "c", "d" };

            var expectedC = new[] { "a", "c", "c", "d" };

​

            var groupA = sequenceA

                .GroupBy(x => x)

                .ToDictionary(keySelector => keySelector.Key, valueSelector => new Stack<string>(valueSelector.ToList()));

​

            var itensToRemove = new List<string>();

​

            foreach (string b in sequenceB)

            {

                Stack<string> itemsA;

​

                if (groupA.TryGetValue(b, out itemsA))

                {

                    itemsA.Pop();

​

                    itensToRemove.Add(b);

​

                    if (!itemsA.Any())

                    {

                        groupA.Remove(b);

                    }

                }

            }

​

            var sequenceC = sequenceB.ToList();

​

            foreach (var toRemove in itensToRemove)

                sequenceC.Remove(toRemove);

​

            Console.WriteLine(string.Concat("Esperado:  ",  JsonConvert.SerializeObject(expectedC)));

            Console.WriteLine(string.Concat("Realizado: ",  JsonConvert.SerializeObject(sequenceC)));

        }

    }

}

​