C#集合之链表的用法

　　　　　　public class PriorityDocumentManager
          {
            private readonly LinkedList<Document> documentList;
               
            // priorities 0.9
            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 d)
            {
              //Contract.Requires<ArgumentNullException>(d != null, "argument d must not be null");
              if (d == null) throw new ArgumentNullException("d");

              AddDocumentToPriorityNode(d, d.Priority);
            }

            private void AddDocumentToPriorityNode(Document doc, int priority)
            {
                    if (priority > 9 || priority < 0)
                        throw new ArgumentException("Priority must be between 0 and 9");

              //检查优先级列表priorityNodes中是否有priority这个优先级
              if (priorityNodes[priority].Value == null)
              {
                //如果没有，递减优先级值，递归AddDocumentToPriorityNode方法，检查是否有低一级的优先级
                --priority;
                if (priority >= 0)
                {
                  AddDocumentToPriorityNode(doc, priority);
                }
                else //如果已经没有更低的优先级时，就直接在链表中添加该节点，并将这个节点添加到优先级列表
                {
                  documentList.AddLast(doc);
                  priorityNodes[doc.Priority] = documentList.Last;
                }
                return;
              }
              else //优先级列表priorityNodes中有priority这个优先级
              {
                LinkedListNode<Document> prioNode = priorityNodes[priority];
                //区分优先级列表priorityNodes存在这个指定的优先级值的节点，还是存在较低的优先级值的节点
                if (priority == doc.Priority)
                // 如果存在这个指定的优先级值的节点
                {
                  //将这个节点添加到链表
                  documentList.AddAfter(prioNode, doc);

                  // 将这个节点赋予优先级列表中的这个优先级值的节点，因为优先级节点总是引用指定优先级节点的最后一个文档
                  priorityNodes[doc.Priority] = prioNode.Next;
                }
                else //如果存在较低的优先级值的节点
                {
                  //在链表中找到这个较低优先级的第一个节点，把要添加的节点放到它前面
                  LinkedListNode<Document> firstPrioNode = prioNode;
                    //通过循环，使用Previous找到这个优先级的第一个节点
                  while (firstPrioNode.Previous != null &&
                     firstPrioNode.Previous.Value.Priority == prioNode.Value.Priority)
                  {
                    firstPrioNode = prioNode.Previous;
                    prioNode = firstPrioNode;
                  }

                  documentList.AddBefore(firstPrioNode, doc);

                  // 设置一个新的优先级节点
                  priorityNodes[doc.Priority] = firstPrioNode.Previous;
                }
              }
            }

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

            // returns the document with the highest priority
            // (that's first in the linked list)
            public Document GetDocument()
            {
              Document doc = documentList.First.Value;
              documentList.RemoveFirst();
              return doc;
            }

          }

          //存储在链表中的元素是Document类型
          public 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)
            {
              this.Title = title;
              this.Content = content;
              this.Priority = priority;
            }
          }

    static void Main()
        {
          PriorityDocumentManager pdm = new PriorityDocumentManager();
          pdm.AddDocument(new Document("one", "Sample", 8));
          pdm.AddDocument(new Document("two", "Sample", 3));
          pdm.AddDocument(new Document("three", "Sample", 4));
          pdm.AddDocument(new Document("four", "Sample", 8));
          pdm.AddDocument(new Document("five", "Sample", 1));
          pdm.AddDocument(new Document("six", "Sample", 9));
          pdm.AddDocument(new Document("seven", "Sample", 1));
          pdm.AddDocument(new Document("eight", "Sample", 1));

          pdm.DisplayAllNodes();

          Console.ReadKey();

        }