using System;

using System.Text.RegularExpressions;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        string sample = "<h1>Title 1</h1>" + "Article text1" + "<h1>Title 2</h1>" + "Article text2" + "<h1>Title 3</h1>" + "Article text3";

        // string.split - by multiple character delimiter

        // Credit: https://stackoverflow.com/a/1254596/12511801

        string[] arr = sample.Split(new string[]{"</h1>"}, StringSplitOptions.None);

        // I store the "title" and "article" in separated lists - their content will be unified later:

        List<string> titles = new List<string>();

        List<string> articles = new List<string>();

        // Loop the splitted text by "</h1>": 

        foreach (string s in arr)

        {

            if (s.StartsWith("<h1>"))

            {

                titles.Add(s.Split(new string[]{"<h1>"}, StringSplitOptions.None)[1]);

            }

            else

            {

                if (s.Contains("<h1>"))

                {

                    // Position 0 is the article and the 1 position is the title: 

                    articles.Add(s.Split(new string[]{"<h1>"}, StringSplitOptions.None)[0]);

                    titles.Add(s.Split(new string[]{"<h1>"}, StringSplitOptions.None)[1]);

                }

                else

                {

                    // Leading text - it's an article by default.

                    articles.Add(s.Split(new string[]{"<h1>"}, StringSplitOptions.None)[0]);

                }

            }

        }

​

        /*

        // NOTE: Printing the current results in the individual lists.

        Console.WriteLine("Amount of titles: " + titles.Count.ToString());

        foreach (string t in titles)

        {

            Console.WriteLine("Title: " + t);

        }

​

        Console.WriteLine("Amount of articles: " + articles.Count.ToString());

        foreach (string a in articles)

        {

            Console.WriteLine("Article: " + a);

        }

        */

        // ------------

        // Create a list of lists.

        // Credit: https://stackoverflow.com/a/12628275/12511801

        List<List<string>> myList = new List<List<string>>();

        for (int i = 0; i < titles.Count; i++)

        {

            myList.Add(new List<string>{"Title: " + titles[i], "Article: " + articles[i]});

        }

​

        // Print the results: 

        foreach (List<string> subList in myList)

        {

            foreach (string item in subList)

            {

                Console.WriteLine(item);

            }

        }

    }

}