创建.net优先队列

有时可能需要一种操作与Queue类似的数据结构，但要根据一种特定的顺序返回对象。向这个队列增加对象时，要根据其优先级放入队列的适当位置。在从队列获取对象时，队列可以根据优先级返回最高或最低的元素。

范型优先队列类：

public   class  PriorityQueue < T >  : IEnumerable, ICloneable
         ... {
            public PriorityQueue() ...{}
            //指定自定义的比较接口
            public PriorityQueue(IComparer<T> icomparer)
            ...{
                specialComparer = icomparer;
            }


            protected List<T> internalQueue = new List<T>();
            protected IComparer<T> specialComparer = null;


            public int Count
            ...{
                get ...{return (internalQueue.Count);}
            }

            public void Clear()
            ...{
                internalQueue.Clear();
            }

            public object Clone()
            ...{
                // Make a new PQ and give it the same comparer
                PriorityQueue<T> newPQ = new PriorityQueue<T>(specialComparer);
                newPQ.CopyTo(internalQueue.ToArray(),0);
                return newPQ;    
            }

            public int IndexOf(T item)
            ...{
                return (internalQueue.IndexOf(item));
            }

            public bool Contains(T item)
            ...{
                return (internalQueue.Contains(item));
            }

            public int BinarySearch(T item)
            ...{
                return (internalQueue.BinarySearch(item, specialComparer));
            }

            public bool Contains(T item, IComparer<T> specialComparer)
            ...{
                if (internalQueue.BinarySearch(item, specialComparer) >= 0)
                ...{
                    return (true);
                }
                else
                ...{
                    return (false);
                }
            }

            public void CopyTo(T[] array, int index)
            ...{
                internalQueue.CopyTo(array, index);
            }

            public virtual T[] ToArray()
            ...{
                return (internalQueue.ToArray());
            }

            public virtual void TrimExcess()
            ...{
                internalQueue.TrimExcess();
            }

            public void Enqueue(T item)
            ...{
                internalQueue.Add(item);
                internalQueue.Sort(specialComparer);
            }

            public T DequeueSmallest()
            ...{
                T item = internalQueue[0];
                internalQueue.RemoveAt(0);

                return (item);
            }

            public T DequeueLargest()
            ...{
                T item = internalQueue[internalQueue.Count - 1];
                internalQueue.RemoveAt(internalQueue.Count - 1);

                return (item);
            }

            public T PeekSmallest()
            ...{
                return (internalQueue[0]);
            }

            public T PeekLargest()
            ...{
                return (internalQueue[internalQueue.Count - 1]);
            }

            public IEnumerator GetEnumerator()
            ...{
                return (internalQueue.GetEnumerator());
            }
        }

 实现了比较接口的字符串比较程序：

public   class  CompareStrLen < T >  : IComparer < T >
             where  T: IComparable < T >
         ... {
            public int Compare(T obj1, T obj2)
            ...{
                int result = 0;
                if ((obj1 is string) && (obj2 is string))
                ...{
                    result = CompareStrings(obj1 as string, obj2 as string);
                }
                else
                ...{
                    // Default to the objects comparison algorithm
                    result = Compare(obj1, obj2);
                }
                return (result);
            }

            private int CompareStrings(string str1, string str2)
            ...{
                if (str1.Length == str2.Length)
                ...{
                    return (0);
                }
                else if (str1.Length > str2.Length)
                ...{
                    return (1);
                }
                else
                ...{
                    return (-1);
                }
            }

            public bool Equals(T item1, T item2)
            ...{
                return (item1.Equals(item2));
            }

            public int GetHashCode(T obj)
            ...{
                return (obj.GetHashCode());
            }
        }

测试程序：

public   static   void  CreatePriorityQueue()
         ... {
            // Create List of messages
            List<string> msgs = new List<string>();
            msgs.Add("foo");
            msgs.Add("This is a longer message.");
            msgs.Add("bar");
            msgs.Add(@"Message with odd characters
                   !@#$%^&*()_+=-0987654321~|}{[]/;:?/>.<,");
            msgs.Add(@"<                                                                   
                      >");
            msgs.Add("onetwothree" + 
                "four");
            msgs.Add("");
            msgs.Add("1234567890");

            // Create a Priority Queue with the appropriate comparer
            CompareStrLen<string> comparer = new CompareStrLen<string>();
            PriorityQueue<string> pqueue = new PriorityQueue<string>(comparer);

            // Add all messages from the List to the priority queue
            foreach (string msg in msgs)
            ...{
                pqueue.Enqueue(msg);
            }

            // Display messages in the queue in order of priority
            foreach (string msg in pqueue)
            ...{
                Console.WriteLine("Msg: " + msg);
            }

            Console.WriteLine("pqueue.Count == " + pqueue.Count);
            //pqueue.Clear();
            //Console.WriteLine("pqueue.Count == " + pqueue.Count);

            Console.WriteLine("pqueue.IndexOf('bar') == " + pqueue.IndexOf("bar"));
            Console.WriteLine("pqueue.IndexOf('_bar_') == " + pqueue.IndexOf("_bar_"));

            Console.WriteLine("pqueue.Contains('bar') == " + pqueue.Contains("bar"));
            Console.WriteLine("pqueue.Contains('_bar_') == " + pqueue.Contains("_bar_"));

            Console.WriteLine("pqueue.BinarySearch('bar') == " + pqueue.BinarySearch("bar"));
            Console.WriteLine("pqueue.BinarySearch('_bar_') == " + pqueue.BinarySearch("_bar_"));
            
            // Dequeue messages starting with the smallest
            int currCount = pqueue.Count;
            for (int index = 0; index < currCount; index++)
            ...{
                // In order to dequeue messages starting with the largest uncomment 
                //   the following line and comment the following lines that 
                //   dequeue starting with the smallest message
                //Console.WriteLine("pqueue.DequeueLargest(): " + 
                //                  pqueue.DequeueLargest().ToString());

                Console.WriteLine("pqueue.DequeueSmallest(): " + 
                    pqueue.DequeueSmallest().ToString());
            }
        
        }