using System;using System.Diagnostics; 

​

public static class Extensions 

{

    /// <summary>

    /// Get a substring between two anchor strings, minimal span

    /// </summary>

    /// <param name="s">source string</param>

    /// <param name="from">search from end of this string</param>

    /// <param name="to">to beginning of this string, searching backwards, from end to start of s</param>

    /// <returns>a substring between from and to, maximal span</returns>

    public static string GetFirstStringBetweenStringsMinSpanCleanup(this string s, string from, string to)

    {

        if (string.IsNullOrEmpty(s) || string.IsNullOrEmpty(from) || string.IsNullOrEmpty(to)) return string.Empty;

​

        int idxFrom = s.IndexOf(from);

        int idxStart = idxFrom + from.Length; //we filter "not found" -1, never race condtn

​

        if (idxFrom == -1 || idxStart >= s.Length - 1)

            return string.Empty;

​

        int idxEnd = s.IndexOf(to, idxStart); //Exact definition, but intuitively next line meets likely expectations -> YOU CHOOSE

        //int idxEnd = s.IndexOf(to, idxStart + 1); //Start next position after, leaving a space for 1 character to be returned

​

        if (idxEnd == -1 || idxEnd <= idxStart)

            return string.Empty;

​

        return s.Substring(idxStart, idxEnd - idxStart);

​

    }

    /// <summary>

    /// Get a substring between two anchor strings, MINIMAL SPAN

    /// </summary>

    /// <param name="s">source string</param>

    /// <param name="from">search from end of this string</param>

    /// <param name="to">to beginning of this string, searching backwards, from end to start of s</param>

    /// <returns>a substring between from and to, maximal span</returns>

    public static string GetFirstStringBetweenStringsMinSpan(this string s, string from, string to)

    {

        Console.Write("args from {0} to {1} = ", from, to); //debug

​

        //edge cases

        if (string.IsNullOrEmpty(s) || string.IsNullOrEmpty(from) || string.IsNullOrEmpty(to)) return string.Empty;

        //if (from.Length >= s.Length || to.Length >= s.Length) return string.Empty; //redundant, this Rule take care of below

​

        int idxFrom = s.IndexOf(from);

        int idxStart = idxFrom + from.Length; //we filter "not found" -1, never race condtn

​

        if (idxFrom == -1)       

            return string.Empty;

        else if (idxStart >= s.Length - 1) //for testing combine to 1 line, we combining a idx with a length, and w/ lengths we normally subtract 1 

        {

            Console.WriteLine("r1. idxStart={0} >= (s.Length - 1)={1}", idxStart, s.Length - 1);

            return string.Empty; 

        }

​

        int idxEnd = s.IndexOf(to, idxStart); //Exact definition, but intuitively next line meets likely expectations -> YOU CHOOSE

        //int idxEnd = s.IndexOf(to, idxStart + 1); //Start next position after, leaving a space for 1 character to be returned

​

        if (idxEnd == -1 )

            return string.Empty;

        else if (idxEnd > s.Length - 1) //Rule 2 never gets used

        {

            Console.WriteLine("r2. idxEnd={0} > (s.Length - 1)={1}", idxEnd, s.Length - 1);

            return string.Empty;

        }

        else if (idxEnd <= idxStart)

        {

            Console.WriteLine("r3. idxEnd={0} <= idxStart={1}", idxEnd, idxStart);

            return string.Empty;

        }

​

        return s.Substring(idxStart, idxEnd - idxStart);

​

    }

 }

​

public class Program

{

    public static void Main()

    {

          string test = "abcd";

            Console.WriteLine(test);

            Console.WriteLine("=================");

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(null, null));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("", ""));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, test));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("", test));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test,""));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "d"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "e"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("e", "e"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "b"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "c"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a","abc"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("b", "abc"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("c", "abc"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("d", "abc"));

​

            Console.WriteLine(); 

            test = "abcdabcd";

            Console.WriteLine(test);

            Console.WriteLine("=================");

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(null, null));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("", ""));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, test));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("", test));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, ""));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "d"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "e"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("e", "e"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "b"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "c"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "abc"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("b", "abc"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("c", "abc"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("d", "abc"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "d")); //pass

​

​

            Console.WriteLine();

            test = "aaaa";

            Console.WriteLine(test);

            Console.WriteLine("=================");

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("aa", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("aaa", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("aaaa", "a"));

​

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "aa"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "aaa"));

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "aaaa"));

​

            Console.WriteLine();

            test = "aaaaaaaaaaaaaaaaaaaaaaaaaaaabbbb";

            Console.WriteLine(test);

            Console.WriteLine("=================");

            Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("bbbb", "aaaa"));

​

            string result = string.Empty; 

            Stopwatch sw = new Stopwatch();

            sw.Start();

            result = test.GetFirstStringBetweenStringsMinSpan("aaaaaaa", "bb");

            sw.Stop();

            Console.WriteLine(result);

            Console.WriteLine(" in " + sw.ElapsedTicks + " ticks."); 

    }

}