Set Cover

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SetCover
{
    class Program
    {
        static void Main(string[] args)
        {
            HashSet<int> universe = Console.ReadLine().Split(", ").Select(e => int.Parse(e)).ToHashSet();

            List<HashSet<int>> sets = new List<HashSet<int>>();

            while (true)
            {
                string input = Console.ReadLine();
                if (string.IsNullOrEmpty(input))
                {
                    break;
                }

                HashSet<int> set = new HashSet<int>(input.Split(", ").Select(e => int.Parse(e)));
                sets.Add(set);
            }

            HashSet<int> maxSet = sets.OrderByDescending(s => s.Count).FirstOrDefault();
            //HashSet<int> targetUniverse = new HashSet<int>();
            List<HashSet<int>> resultSets = new List<HashSet<int>>();

            resultSets.Add(maxSet);
            sets.RemoveAt(0);

            if (!universe.SequenceEqual(resultSets[0]))
            {

                while (sets.Count > 0)
                {
                    HashSet<int> targetUniverse = resultSets.SelectMany(s => s).ToHashSet();
                    HashSet<int> greedySet = GetGreedySet(targetUniverse, sets);

                    if (!greedySet.All(e => resultSets.SelectMany(s => s).Contains(e)))
                    {
                        resultSets.Add(greedySet);


                        int[] current = resultSets.SelectMany(s => s).Distinct().OrderBy(i => i).ToArray();
                        if (universe.SequenceEqual(current))
                        {
                            break;
                        }
                    }

                    sets.Remove(greedySet);
                }

                int[] resultSet = resultSets.SelectMany(s => s).Distinct().OrderBy(i => i).ToArray();
                if (!universe.SequenceEqual(resultSet))
                {
                    Console.WriteLine("Error");
                    return;
                }
            }

            StringBuilder stringBuilder = new StringBuilder();

            stringBuilder.AppendLine($"Sets to take ({resultSets.Count}):");

            foreach (HashSet<int> set in resultSets)
            {
                stringBuilder.AppendLine(string.Join(", ", set));
            }

            Console.WriteLine(stringBuilder.ToString().TrimEnd());
        }

        private static HashSet<int> GetGreedySet(HashSet<int> universe, List<HashSet<int>> sets)
        {
            HashSet<int> greedySet = sets[0];
            sets.RemoveAt(0);

            foreach (HashSet<int> set in sets)
            {
                HashSet<int> current = new HashSet<int>(set);
                current.ExceptWith(universe);
                if (current.Count > greedySet.Count)
                {
                    greedySet = set;
                }
            }

            return greedySet;
        }
    }
}