using System;

using System.Text.RegularExpressions;

using System.Net;

using System.Collections.Generic;

using System.Linq;

​

​

public class Program

{

    //Removes Html Tags from input provided

    public static string RemoveHtmlTags(string html)

    {

        string htmlRemoved = Regex.Replace(html, @"<script[^>]*>[\s\S]*?</script>|<[^>]+>| ", " ").Trim();

        string normalised = Regex.Replace(htmlRemoved, @"\s{2,}", " ");

        return normalised;

    }

    public static void Main()

    {

        using (WebClient client = new WebClient())

        { 

            //get the page source

            string html = client.DownloadString("http://stackoverflow.com/").ToLower();

            //remove html elements

            html = RemoveHtmlTags(html);

            //split list into keywords by space characters

            List<string> list = html.Split(' ').ToList();

            //remove any non alphabet characters

            var onlyAlphabetRegEx = new Regex(@"^[A-z]+$");

            list = list.Where(f => onlyAlphabetRegEx.IsMatch(f)).ToList();

​

            //further blacklist words (greater than 2 characters, not important, etc..)

            string[] blacklist = { "a", "an", "on", "of", "or", "as", "i", "in", "is", "to", "the", "and", "for", "with", "not", "by" }; //add your own

            list = list.Where(x => x.Length > 2).Where(x => !blacklist.Contains(x)).ToList();

            //distict keywords by key and count, and then order by count.

            var keywords = list.GroupBy(x => x).OrderByDescending(x => x.Count());

​

            //print each keyword to console.

            foreach (var word in keywords)

            {

                Console.WriteLine("{0} {1}", word.Key, word.Count());

            }

        } 

    }

}