C# .NET - how to read duplicate Ids in a html Document using ASp.Net C#

I Need to Develop an http://asp.net/ page that reads html files  in a folder and displays list of duplicate ids. ie. Same id used with-in one or more html files

a.html

          <div id=”a1”> </div> <ul id=”a2”> <li> Hello </li> <li> how are you</li></ul>

b.html

          <ul id=”a1></ul> <div id=”a3”> <ul> <li> Val 1</li><li>Val2</li> </ul></div>

 

The program should display the following result:

 

                  ID        Files

                  A1       a.html, b.html Any one help me Please. Thanks in Advance.

For this you need to do via File handler read the files content and if fount id then find next " then started reading in another variable and then split with " like id="ramendra"
now you have rame ndra store in a global array
now mathc this id in all of your files and do whatever you wish.
happy coding