Test if all values in a list are unique

Question

I have a small list of bytes and I want to test that they\'re all different values. For instance, I have this:

List theList = new List

        

Answer 1

Okay, here is the most efficient method I can think of using standard .Net

using System;
using System.Collections.Generic;

public static class Extension
{
    public static bool HasDuplicate(
        this IEnumerable source,
        out T firstDuplicate)
    {
        if (source == null)
        {
            throw new ArgumentNullException(nameof(source));
        }

        var checkBuffer = new HashSet();
        foreach (var t in source)
        {
            if (checkBuffer.Add(t))
            {
                continue;
            }

            firstDuplicate = t;
            return true;
        }

        firstDuplicate = default(T);
        return false;
    }
}

essentially, what is the point of enumerating the whole sequence twice if all you want to do is find the first duplicate.

I could optimise this more by special casing an empty and single element sequences but that would depreciate from readability/maintainability with minimal gain.