using System;

using System.Collections.Specialized;

public class Program

{   /// <summary>

    /// Take these inputs and find all of the different patterns in sourceString of length patternLength and output

    /// all of the patterns that occur more than once and the number of times they occur.

    /// </summary>

    static StringCollection Fiddle(string sourceString, int patternLength)

    {

        StringCollection myCol = new StringCollection();

        var lastPatternIndex = sourceString.Length - patternLength;

        // There is some assumption checks

        if (patternLength <= 0)

            throw new ArgumentOutOfRangeException("patternLength","pattern lenght must be positive.");

        if (lastPatternIndex <= 0)

            throw new ArgumentOutOfRangeException("sourceString","sourceString must be longer then pattern length.");

        if (lastPatternIndex > Int32.MaxValue)

           throw new ArgumentOutOfRangeException("sourceString","sourceString must be shotter then max int value, for make Substring working.");

        for (var index = 0; index <= lastPatternIndex; ++index)

        {

            var pattern = sourceString.Substring(index, patternLength);

            for (var subindex = 0; subindex < index; ++subindex)

            {

                if (pattern == sourceString.Substring(subindex, patternLength))

                {

                    if (!myCol.Contains(pattern))

                        myCol.Add(pattern);

                }

            }

        }

        return myCol;

    }

​

    public static void Main()

    {

        // For example, when searching the string "zfabcde224lkfabc51+crsdtab=", with a specified pattern length of 3,

        // the method should return the patterns "fab" and "abc" with an occurrence value of two for each of the patterns.

        var result = Fiddle("zfabcde224lkfabc51+crsdtab=", 3);

        foreach(var line in result) 

            Console.WriteLine(line);

    }

}