双向链表LinkedList的使用

class Document
    {
        public string Title { get; private set; }
        public string Content { get; private set; }
        public byte Priority { get; private set; }

        public Document(string title, string content, byte priority = 0)
        {
            this.Title = title;
            this.Content = content;
            this.Priority = priority;
        }
    }

class PriorityDocumentManager
    {
        private readonly LinkedList<Document> documentList;
        private readonly List<LinkedListNode<Document>> priorityNodes;

        public PriorityDocumentManager()
        {
            documentList = new LinkedList<Document>();
            priorityNodes = new List<LinkedListNode<Document>>(10);
            for (int i = 0; i < 10; i++)
            {
                priorityNodes.Add(new LinkedListNode<Document>(null));
            }
        }

        public void AddDocument(Document doc)
        {
            if (doc == null)
            {
                throw new ArgumentNullException("doc");
            }
            AddDocumentToPriorityNode(doc, doc.Priority);
        }

        private void AddDocumentToPriorityNode(Document doc, int priority)
        {
            if (priority > 9 || priority < 0)
            {
                throw new ArgumentException("优先级必须大于0小于9");
            }

            if (priorityNodes[priority].Value == null)
            {
                --priority;
                if (priority >= 0)
                {
                    AddDocumentToPriorityNode(doc, priority);
                }
                else
                {
                    documentList.AddLast(doc);
                    priorityNodes[doc.Priority] = documentList.Last;
                }

                return;
            }
            else
            {
                LinkedListNode<Document> prioNode = priorityNodes[priority];
                if (priority == doc.Priority)
                {
                    documentList.AddAfter(prioNode, doc);
                    priorityNodes[doc.Priority] = prioNode.Next;
                }
                else
                {
                    LinkedListNode<Document> firstPrioNode = prioNode;
                    while (firstPrioNode.Previous != null && firstPrioNode.Previous.Value.Priority == prioNode.Value.Priority)
                    {
                        firstPrioNode = prioNode.Previous;
                        prioNode = firstPrioNode;
                    }

                    documentList.AddBefore(firstPrioNode, doc);

                    priorityNodes[doc.Priority] = firstPrioNode.Previous;
                }
            }
        }

        public void DisplayAllNodes()
        {
            foreach (var doc in documentList)
            {
                Console.WriteLine("priority: {0}, title: {1}", doc.Priority, doc.Title);
            }
        }

        public Document GetDocument()
        {
            Document doc = documentList.First.Value;
            documentList.RemoveFirst();
            return doc;
        }
    }

            PriorityDocumentManager pdm = new PriorityDocumentManager();
            pdm.AddDocument(new Document("one", "content", 3));
            pdm.AddDocument(new Document("two", "content", 1));
            pdm.AddDocument(new Document("three", "content", 2));
            pdm.AddDocument(new Document("six", "content", 4));
            pdm.DisplayAllNodes();