GroupNumbers

namespace GroupNumbers
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;

    public class Startup
    {
        private static Dictionary<int, HashSet<int>> matrixImitation;
        private static int currentIndex;

        public static void Main()
        {
            matrixImitation = new Dictionary<int, HashSet<int>>
            {
                [0] = new HashSet<int>(),
                [1] = new HashSet<int>(),
                [2] = new HashSet<int>()
            };

            currentIndex = 0;

            int[] allElements = Console.ReadLine()
                                .Split(new[] { ',', ' ' }, StringSplitOptions.RemoveEmptyEntries)
                                .Select(ParseStringsAndPlaceThemWhereNeeded)
                                .ToArray();

            StringBuilder result = new StringBuilder();
            foreach (KeyValuePair<int, HashSet<int>> kvp in matrixImitation)
            {
                foreach (int indexOfElement in kvp.Value)
                {
                    result.Append(allElements[indexOfElement]);
                    result.Append(" ");
                }

                result.AppendLine();
            }

            Console.Write(result);
        }

        private static int ParseStringsAndPlaceThemWhereNeeded(string toParse)
        {
            int number = int.Parse(toParse);

            int remainder = Math.Abs(number) % 3;

            matrixImitation[remainder].Add(currentIndex);

            currentIndex++;

            return number;
        }
    }
}