using System;

using System.Collections.Generic;

using System.Linq;

​

public class PatternCount

    {

        public int Count { get; set; }

        public string Pattern { get; set; }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Enter input string:");

            var searchString = Console.ReadLine();

            Console.WriteLine("Enter input length:");

​

            var minOccurance = 2;

            if (int.TryParse(Console.ReadLine(), out int patternLen))

            {

                var patterns = CountAndFilterInput(searchString, patternLen, minOccurance);

                Console.WriteLine("Patterns:");

                foreach (var pattern in patterns)

                {

                    Console.WriteLine($"{pattern.Pattern} => {pattern.Count}");

                }

            }

            else

            {

                Console.WriteLine("Please enter a valid number..");

            }

​

            Console.ReadLine();

        }

​

        public static IEnumerable<string> InputString(string input, int size)

        {

            for (int i = 0; i + size <= input.Length; i++)

            {

                yield return input.Substring(i, size);

            }

        }

​

        public static List<PatternCount> CountAndFilterInput(string input, int size, int minCount)

        {

            if (string.IsNullOrEmpty(input))

            {

                throw new ArgumentException("Please enter valid input.");

            }

​

            if (size <= 0)

            {

                throw new ArgumentOutOfRangeException("Pattern length should greater than zero.");

            }

​

            var result = (from pattern in InputString(input, size)

                          group pattern by pattern into grouping

                          where grouping.Count() >= minCount

                          select new PatternCount

                          {

                              Pattern = grouping.Key,

                              Count = grouping.Count()

                          }).ToList();

​

            return result;

        }

    }