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

you may use HashSet:

 static void Main()
    {
        string textWithDuplicates = "aaabbcccggg";

        Console.WriteLine(textWithDuplicates.Count());  
        var letters = new HashSet(textWithDuplicates);
        Console.WriteLine(letters.Count());

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