prioritydocumentmanager.cs

来自「C#高级编程第6版随书源代码 值得下载」· CS 代码 · 共 99 行

using System;
using System.Collections.Generic;
using System.Text;

namespace Wrox.ProCSharp.Collections
{
   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)
      {
         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");

         if (priorityNodes[priority].Value == null)
         {
            priority--;
            if (priority >= 0)
            {
               // check for the next lower priority
               AddDocumentToPriorityNode(doc, priority);
            }
            else // now no priority node exists with the same priority or lower
                 // add the new document to the end 
            {
               documentList.AddLast(doc);
               priorityNodes[doc.Priority] = documentList.Last;
            }
            return;
         }
         else // a priority node exists
         {
            LinkedListNode<Document> priorityNode = priorityNodes[priority];
            if (priority == doc.Priority)     // priority node with the same
                                              // priority exists
            {
               documentList.AddAfter(priorityNode, doc);

               // set the priority node to the last document with the same priority
               priorityNodes[doc.Priority] = priorityNode.Next;
            }
            else // only priority node with a lower priority exists
            {
               // get the first node of the lower priority
               LinkedListNode<Document> firstPriorityNode = priorityNode;
               while (firstPriorityNode.Previous != null &&
                      firstPriorityNode.Previous.Value.Priority == 
                            priorityNode.Value.Priority)
               {
                  firstPriorityNode = priorityNode.Previous;
               }

               documentList.AddBefore(firstPriorityNode, doc);

               // set the priority node to the new value
               priorityNodes[doc.Priority] = firstPriorityNode.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;
      }
   }

}