gistfile1.cs

 interface IMyList<T> : IEnumerable<T>
    {
        // O(1)
        // Add an item at the beginning of the list.
        void AddFirst(T item);

        // O(1)
        // Add an item at the end of the list.
        void AddLast(T item);

        // O(1)
        // Remove the item from the list. If the list contains multiple
        // copies/references of the item, remove one of them.
        void Remove(T item);

        // O(1)
        // Reverse the list.
        void Reverse();
    }

    /// <summary>
    /// 没有检查 乱写的 By Wayne
    /// </summary>
    /// <typeparam name="T"></typeparam>
    class MyList<T> : IMyList<T> where T : class
    {
        LinkedList<T> _leftLinkedList = new LinkedList<T>();
        LinkedList<T> _rightLinkedList = new LinkedList<T>();
        Dictionary<T, List<LinkedListNode<T>>> _index = new Dictionary<T, List<LinkedListNode<T>>>();

        public MyList()
        {

        }


        public void AddFirst(T item)
        {
            if (item == null)
            {
                throw new ArgumentNullException();
            }
            var ln = _leftLinkedList.AddLast(item);
            List<LinkedListNode<T>> lst;
            if (!_index.TryGetValue(item, out lst))
            {

                lst = new List<LinkedListNode<T>>();
                _index.Add(item,lst);

            }
            
            lst.Add(ln);

        }


        public void AddLast(T item)
        {
            if (item == null)
            {
                throw new ArgumentNullException();
            }
            var ln = _rightLinkedList.AddLast(item);
            List<LinkedListNode<T>> lst;
            if (!_index.TryGetValue(item, out lst))
            {

                lst = new List<LinkedListNode<T>>();
                _index.Add(item, lst);

            }
            lst.Add(ln);
        }

        public void Remove(T item)
        {
            if (item == null)
            {
                throw new ArgumentNullException();
            }
            List<LinkedListNode<T>> lst;
            if (_index.TryGetValue(item, out lst))
            {

            
                if (lst.Count>0)
                {
                    var lastp = lst.Count - 1;
                    var ln = lst[lastp];
                    ln.List.Remove(ln);
                    lst.RemoveAt(lastp);
                }
                

            }
        }

        public void Reverse()
        {
            var mid = _leftLinkedList;
            _leftLinkedList = _rightLinkedList;
            _rightLinkedList = mid;
        }

        public IEnumerator<T> GetEnumerator()
        {
            return GetEnumerable();
        }

        private IEnumerator<T> GetEnumerable()
        {
            var current = _leftLinkedList.Last;
            while (current != null)
            {
                yield return current.Value;
                current = current.Previous;
            }

            current = _rightLinkedList.First;
            while (current != null)
            {
                yield return current.Value;
                current = current.Next;
            }
        }

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }
    }