using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public class PatternLength

    {

        public int qty { get; set; }

        public string characters { get; set; }

    }

    public static void Main()

    {

        int length = 0;

        string str = "";

        string Verlength = "";

        string ret = string.Empty;

        int TotOcc = 0;

​

        Console.WriteLine("Enter String(Field can not be empty): ");

        str = Console.ReadLine();

        if (String.IsNullOrEmpty(str))

        {

            Console.WriteLine("The String field is empty!");

            return;

        }

        Console.WriteLine("Enter Pattern Length(Field can not be empty and must be an integer): ");

        Verlength = Console.ReadLine();

        if (String.IsNullOrEmpty(Verlength))

        {

            Console.WriteLine("The Pattern Length field is empty!");

            return;

        }

        else

        {

            try

            {

                length = Convert.ToInt32(Verlength);

            }

            catch (Exception)

            {

                Console.WriteLine("Please enter an integer number in the Pattern Length field!");

                return;

                throw;

            }

​

        }

​

         if (str.Length < length)

         {

             Console.WriteLine("The length of the string can not be less than Patter Length!");

             return;

         }

        var PatternLengths = new List<PatternLength>();

​

        if (str.Length == length)

            {

                PatternLengths.Add(new PatternLength { qty = 1, characters = str });

            }

            else

            {

                for (int i = 0; i <= str.Length - length; i++)

                {

                    ret = str.Substring(i, length);

                    PatternLengths.Add(new PatternLength { qty = 1, characters = ret });

                }

            }

        for (int i = 0; i < str.Length - length; i++)

        {

            ret = str.Substring(i, length);

            PatternLengths.Add(new PatternLength { qty = 1, characters = ret });

        }

​

        var Totals =

            from PatternLength in PatternLengths

            group PatternLength by PatternLength.characters into PatternLengthGroup

            select new

            {

                characters = PatternLengthGroup.Key,

                Totalqty = PatternLengthGroup.Sum(x => x.qty),

            };

​

        if(Totals.Count() > 0)

        {

            foreach (var item in Totals)

            {

                if (item.Totalqty > 1)

                    {

                        Console.WriteLine("Occurrences: " + item.characters + " - " + item.Totalqty.ToString());

                        TotOcc += 1;

                    }

            }

        }

        else

            Console.WriteLine("There are no occurrences !");

        if(TotOcc == 0)

                Console.WriteLine("There are no occurrences !");

    }

}