How can you remove duplicate characters in a string?

Question

I have to implements a function that takes a string as an input and finds the non-duplicate character from this string.

So an an example is if I pass string str = \"

Answer 1

 class Program
    {
        static void Main(string[] args)
        {
            bool[] doesExists = new bool[256];
            String st = Console.ReadLine();
            StringBuilder sb = new StringBuilder();
            foreach (char ch in st)
            {
                if (!doesExists[ch])
                {
                    sb.Append(ch);
                    doesExists[ch] = true;
                }
            }
            Console.WriteLine(sb.ToString());
        }
    }

Answer 2

namespace Demo { class Program {

  static void Main(string[] args) {
     string myStr = "kkllmmnnouo";
     Console.WriteLine("Initial String: "+myStr);
    // var unique = new HashSet<char>(myStr);
     HashSet<char> unique = new HashSet<char>(myStr);
     Console.Write("New String after removing duplicates: ");

     foreach (char c in unique) 
        Console.Write(c);   
  }    } }