using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(new AlphanumericVersionComparer().Compare("1a.2.b.3a", "1a.2.b.3b"));

    }

}

​

/// <summary>

/// Compares two alphanumeric version numbers.

/// </summary>

public class AlphanumericVersionComparer : IComparer<string>

{

    /// <summary>

    /// Compares two alphanumeric version numbers and returns a value

    /// indicating whether one is less than, equal to, or greater than the other.

    /// </summary>

    /// <param name="x">The first alphanumeric version number to compare.</param>

    /// <param name="y">The second alphanumeric version number to compare.</param>

    /// <returns>A signed integer that indicates the relative values of x and y.</returns>

    public int Compare(string x, string y)

    {

        // Validate parameters

        if (x == null) throw new ArgumentNullException("x");

        if (y == null) throw new ArgumentNullException("y");

        // Test for equality

        if (x == y)

            return 0;

        // Split the different parts of the number

        string[] xParts = x.Split('.');

        string[] yParts = y.Split('.');

        // Compare each parts

        AlphanumericComparer alphaNumComparer = new AlphanumericComparer();

        for (int i = 0, n = Math.Max(xParts.Length, yParts.Length); i < n; i++)

        {

            // If the part at index i is not in y => x is greater

            if (i >= yParts.Length)

                return 1;

            // If the part at index i is not in x => y is greater

            if (i >= xParts.Length)

                return -1;

            // Compare the two alphanumerical numbers

            int result = alphaNumComparer.Compare(xParts[i], yParts[i]);

            if (result != 0)

            {

                return result;

            }

        }

        // The two numbers are equal (really??? I thought we tested for equality already!)

        System.Diagnostics.Debug.Fail("Not supposed to reach this code...");

        return 0;

    }

}

​

/// <summary>

/// Compares two alphanumeric strings.

/// </summary>

/// <remarks>See http://snipd.net/alphanumericnatural-sorting-in-c-using-icomparer </remarks>

public class AlphanumericComparer : IComparer<string>

{

    /// <summary>

    /// Compares two alphanumerics and returns a value

    /// indicating whether one is less than, equal to, or greater than the other.

    /// </summary>

    /// <param name="x">The first alphanumeric to compare.</param>

    /// <param name="y">The second alphanumeric to compare.</param>

    /// <returns>A signed integer that indicates the relative values of x and y.</returns>

    public int Compare(string x, string y)

    {

        int len1 = x.Length;

        int len2 = y.Length;

        int marker1 = 0;

        int marker2 = 0;

        // Walk through two the strings with two markers.

        while (marker1 < len1 && marker2 < len2)

        {

            char ch1 = x[marker1];

            char ch2 = y[marker2];

            // Some buffers we can build up characters in for each chunk.

            char[] space1 = new char[len1];

            int loc1 = 0;

            char[] space2 = new char[len2];

            int loc2 = 0;

            // Walk through all following characters that are digits or

            // characters in BOTH strings starting at the appropriate marker.

            // Collect char arrays.

            do

            {

                space1[loc1++] = ch1;

                marker1++;

                if (marker1 < len1)

                {

                    ch1 = x[marker1];

                }

                else

                {

                    break;

                }

            } while (char.IsDigit(ch1) == char.IsDigit(space1[0]));

            do

            {

                space2[loc2++] = ch2;

                marker2++;

                if (marker2 < len2)

                {

                    ch2 = y[marker2];

                }

                else

                {

                    break;

                }

            } while (char.IsDigit(ch2) == char.IsDigit(space2[0]));

            // If we have collected numbers, compare them numerically.

            // Otherwise, if we have strings, compare them alphabetically.

            string str1 = new string(space1);

            string str2 = new string(space2);

            int result;

            if (char.IsDigit(space1[0]) && char.IsDigit(space2[0]))

            {

                int thisNumericChunk = int.Parse(str1);

                int thatNumericChunk = int.Parse(str2);

                result = thisNumericChunk.CompareTo(thatNumericChunk);

            }

            else

            {

                result = str1.CompareTo(str2);

            }

            if (result != 0)

            {

                return result;

            }

        }

        return len1 - len2;

    }

}