using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var tests = new List<string> {

            "twitter.com/test",

            "https://twitter.com/test",

            "http://twitter.com/test",

            "https://twitter.com/test?hello=hello",

            "handle",

            "handle/handle"

        };

​

​

        foreach (var test in tests)

        {

            Console.WriteLine(string.Format("{0}: {1}", test, IsValidUri(test)));

        }

    }

    public static string IsValidUri(string uri)

    {

            String validUri;

            if (uri.IndexOf("/") != -1)

            {

                validUri = new UriBuilder(uri).Uri.AbsolutePath;

                return validUri.Substring(0, 1) == "/" ? validUri.Substring(1) : validUri;

            }

            return uri;

    }

}