Check List for duplications with optional words to exclude

Question

I have a method as below. Method return either false/true either when list contains duplicates or not. I would like to extend my method to say for instance (optional) that i

Answer 1

public static bool ContainsDuplicates(this IEnumerable items, IEnumerable itemsToExclude = null)
{
    if (itemsToExclude == null) itemsToExclude = Enumerable.Empty();
    return items.Except(itemsToExclude)
                .GroupBy(n => n)
                .Any(c => c.Count() > 1);
}

But i'd prefer this implementation because it's more performant:

public static bool ContainsDuplicates(this IEnumerable items, IEnumerable itemsToExclude = null)
{
    if (itemsToExclude == null) itemsToExclude = Enumerable.Empty();
    HashSet set = new HashSet();
    return !items.Except(itemsToExclude).All(set.Add);
}