public static class EnumerableExtensions
    {
        public static bool HasDuplicates<T>(this IEnumerable<T> subjects)
        {
            return HasDuplicates(subjects, EqualityComparer<T>.Default);
        }


        public static bool HasDuplicates<T>(this IEnumerable<T> subjects, IEqualityComparer<T> comparer)
        {
            if(subjects == null)
                throw new ArgumentNullException("subjects");

            if(comparer == null)
                throw new ArgumentNullException("comparer");

            var set = new HashSet<T>(comparer);

            foreach (var s in subjects)
                if (!set.Add(s))
                    return true;

            return false;
        }
    }