TASK: Concatenate and sort two strings. The letters must be distinct in output

C#:

using System;
using System.Linq;
using static System.Console;

namespace demo
{
    class Program
    {
        static void Main(string[] args)
        {
            WriteLine(Longest("aretheyhere", "yestheyarehere")); // "aehrsty"
        }

        public static string Longest(string s1, string s2)
        {
            string str = s1 + s2;
            char[] uniq_str = str.ToCharArray().Distinct().ToArray();
            Array.Sort(uniq_str);
            string result = String.Join("", uniq_str);

            return result;
        }
    }
}

Result:

aehrsty

Better code from a better coder:

public static string Longest(string s1, string s2)
        {
            return new string((s1 + s2).Distinct()
                        .OrderBy(x => x).ToArray());
        }

Reference: Two to One ( Codewars )