using System;

public class Program

{

    public static void Main()

    {

        // Method takes string and char as parameter

        // find shortest substring first and last occurance between char

        // if no match return null

        Console.WriteLine("ShortestString:{0}",ShortestString("wgwanewshwdw",'w'));

    }

    public static string ShortestString(String s, char c)

    {

        if(s == "" || c.ToString() == "")

        {

            return null;

        }

​

        if(s.IndexOf(c) == -1)

        {

             return null;

        }

​

        string  shortestString = "";

        int lenSubString = 0;

        int startIndex = s.IndexOf(c);

        int  endIndex = s.IndexOf(c, startIndex + 1);

        if(endIndex == -1)

        {

            return  null;

        }

        lenSubString = (endIndex - startIndex) -1;

        shortestString = s.Substring(startIndex +1, lenSubString);

        int lenSubStringTemp = 0;

​

        int  index = endIndex;

        while( index < s.Length )

        {

            startIndex = endIndex;

            endIndex = s.IndexOf(c, startIndex + 1);

​

            if(endIndex == -1)

            {

                break;

            }

            lenSubStringTemp  = (endIndex - startIndex) -1;

            if(lenSubStringTemp < lenSubString)

            {

                lenSubString = lenSubStringTemp;

                shortestString = s.Substring(startIndex +1, lenSubString);

            }

​

            index = endIndex;

        }

        return shortestString;

    }

​

}