Simple C# Set with Add and Find methods

public class Set<T> : IEnumerable<T>, IEnumerable
                                 where T: IComparable
    {
        public int Length => Buffer.Count();
        private List<T> Buffer { get; set; }
        private int Pointer { get; set; }

        public Set()
        {
            Buffer = new List<T>();
            Pointer = 0;
        }

        public Set(int size)
        {
            Buffer = new List<T>(size);
            Pointer = 0;
        }

        public Set(IEnumerable<T> initializer)
        {
            Buffer = initializer.OrderBy(x => x).Distinct().ToList();
            Pointer = 0;
        }

        public Set(params T[] initializer)
        {
            Buffer = initializer.OrderBy(x => x).Distinct().ToList();
            Pointer = 0;
        }

        public bool Add(T item)
        {
            if (!Buffer.Contains(item))
            {
                Pointer = GetLeftBorder(item);
                Buffer.Insert(Pointer + 1, item);
                return true;
            }
            return false;
        }

        public T FindNext(T item)
        {
            var itemIndex = Search(item);
            if (itemIndex != -1)
                return Buffer[itemIndex + 1];
            return default(T);
        }

        private int GetLeftBorder(T item)
        {
            var (left, right) = (-1, Buffer.Count());
            return GetLeftBorder(item, left, right);
        }

        private int GetLeftBorder(T item, int left, int right)
        {
            while (!(right <= left + 1))
            {
                var mid = (right - left) / 2 + left;
                if (item.CompareTo(Buffer[mid]) < 0)
                {
                    right = mid;
                    continue;
                }
                left = mid;
            }
            return left;
        }

        private int Search(T item)
        {
            var (left, right) = (0, Buffer.Count()-1);
            while (left < right)
            {
                var mid = (right - left) / 2 + left;
                if (item.CompareTo(Buffer[mid]) <= 0)
                {
                    right = mid;
                    continue;
                }
                left = mid + 1;
            }
            if (Buffer[right].Equals(item))
                return right;
            return -1;
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return this.GetEnumerator();
        }

        public IEnumerator<T> GetEnumerator()
        {
            foreach (var item in Buffer)
            {
                yield return (T)item;
            }
        }

        public T this[int index]
        {
            get
            {
                if (index >= 0 && index < Buffer.Count)
                    return Buffer[index];
                throw new IndexOutOfRangeException($"Недопустимое значение индекса {index}: Вне диапазона");
            }
        }

        public bool EnumerableCompareTo(Set<T> other)
        {
            if (Buffer.Count != other.Length)
                return false;

            var length = other.Length;
            for (int i = 0; i < length; i++)
            {
                if (!this[i].Equals(other[i]))
                    return false;
            }
            return true;
        }

        public bool EqualsTo(Set<T> other)
        {
            return EnumerableCompareTo(other);
        }
    }