集合的概念
集合是由一些確定的、彼此不同的成員或者元素構成的一個整體。如果將緊密相關的數據組合到一個集合中，則能夠更有效地處理這些緊密相關的數據。代替編寫不同的代碼來處理每一單獨的對象，您可以使用相同的調用代碼來處理一個集合的所有元素。

在c#中可以使用 Array 類和 System.Collections 類添加、移除和修改集合中的個別元素或某一范圍內的元素。甚至可以將整個集合復制到另一個集合中。在 .NET Framework 2.0 版中，泛型集合類提供了新功能，并使得創建強類型集合變得容易。

雖然c#中提供了多種集合類可供我們選擇，但為了加深對這種數據類型的理解，構造自己的集合類無疑是最好的選擇。下面給出了基于數組及鏈表兩種實現的集合類。

定義集合實現的接口

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public interface IBag:IEnumerable  
  {  
      void Add(object element);  
      void AddAll(IBag bag);  
      int Size{get;}  
      bool IsEmpty();  
      object RemoveRandom();  
      object Remove(object target);  
      IBag Union(IBag bag);  
      bool Contains(object target);  
  } 
  public interface IBag:IEnumerable
    {
        void Add(object element);
        void AddAll(IBag bag);
        int Size{get;}
        bool IsEmpty();
        object RemoveRandom();
        object Remove(object target);
        IBag Union(IBag bag);
        bool Contains(object target);
    }

基于數組的集合實現

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public class ArrayBag:IBag  
{  
    int DEDAULT_CAPACITY = 1000;  
    Random random = new Random();  
    int count=0;  
    object[] contents;  
    public ArrayBag()  
    {  
        contents = new object[DEDAULT_CAPACITY];  
        //count = 0;  
    }  
    public ArrayBag(int initialCapacity)  
    {  
        contents = new object[initialCapacity];  
       // count = 0;  
    } 
    #region IBag 成員  
    public void Add(object element)  
    {  
        if (Size == contents.Length)  
        {  
            ExpandCapacity();  
        }  
        contents[count] = element;  
        count++;  
    }  
    private void ExpandCapacity()  
    {  
        object[] temp = new object[contents.Length * 2];  
        for (int index = 0; index < contents.Length; index++)  
        {  
            temp[index] = contents[index];  
        }  
        contents = temp;  
    }  
    public void AddAll(IBag bag)  
    {  
        foreach (object o in bag)  
        {  
            Add(o);  
        }  
    }  
    public int Size  
    {  
        get { return count; }  
    }  
    public bool IsEmpty()  
    {  
       return (count==0);  
    }  
    public object RemoveRandom()  
    {  
        if (IsEmpty())  
        {  
            throw new Exception("this colleciton is empty!");  
        }  
        int choice = random.Next(count);  
          
        object result = contents[choice];  
        contents[choice] = contents[count - 1];  
        contents[count - 1] = null;  
        count--;  
        return result;  
    }  
    public object Remove(object target)  
    {  
        if (IsEmpty())  
        {  
            throw new Exception("the collection is empty");  
        }  
        int index = Find(target);  
        if (index == -1)  
        {  
            throw new Exception("not found!");  
        }  
        else 
        {  
            object result = contents[index];  
            contents[index] = contents[count - 1];  
            contents[count - 1] = null;  
            count--;  
            return result;  
        }  
    }  
    private int Find(object target)  
    {  
        for (int i = 0; i < count; i++)  
        {  
            if (contents[i].Equals(target))  
                return i;  
        }  
        return -1;  
    }  
    public IBag Union(IBag bag)  
    {  
        ArrayBag both = new ArrayBag();  
        for (int index = 0; index < count; index++)  
        {  
            both.Add(contents[index]);  
        }  
        foreach (object o in bag)  
        {  
            both.Add(o);  
        }  
        return both;  
    }  
    public bool Contains(object target)  
    {  
        if (Find(target) != -1)  
        {  
            return true;  
        }  
        else 
        {  
            return false;  
        }  
    }  
    public IEnumerator GetEnumerator()  
    {  
        for (int index = 0; index < count; index++)  
        {  
            yield return contents[index];  
        }  
    } 
    #endregion  
    public override string ToString()  
    {  
        StringBuilder sb = new StringBuilder();  
        for (int i = 0; i < count; i++)  
        {  
            sb.Append(contents[i] + " ");  
        }  
        return sb.ToString();  
    }  
} 
    public class ArrayBag:IBag
    {
        int DEDAULT_CAPACITY = 1000;
        Random random = new Random();
        int count=0;
        object[] contents;
        public ArrayBag()
        {
            contents = new object[DEDAULT_CAPACITY];
            //count = 0;
        }
        public ArrayBag(int initialCapacity)
        {
            contents = new object[initialCapacity];
           // count = 0;
        }
        #region IBag 成員
        public void Add(object element)
        {
            if (Size == contents.Length)
            {
                ExpandCapacity();
            }
            contents[count] = element;
            count++;
        }
        private void ExpandCapacity()
        {
            object[] temp = new object[contents.Length * 2];
            for (int index = 0; index < contents.Length; index++)
            {
                temp[index] = contents[index];
            }
            contents = temp;
        }
        public void AddAll(IBag bag)
        {
            foreach (object o in bag)
            {
                Add(o);
            }
        }
        public int Size
        {
            get { return count; }
        }
        public bool IsEmpty()
        {
           return (count==0);
        }
        public object RemoveRandom()
        {
            if (IsEmpty())
            {
                throw new Exception("this colleciton is empty!");
            }
            int choice = random.Next(count);
           
            object result = contents[choice];
            contents[choice] = contents[count - 1];
            contents[count - 1] = null;
            count--;
            return result;
        }
        public object Remove(object target)
        {
            if (IsEmpty())
            {
                throw new Exception("the collection is empty");
            }
            int index = Find(target);
            if (index == -1)
            {
                throw new Exception("not found!");
            }
            else
            {
                object result = contents[index];
                contents[index] = contents[count - 1];
                contents[count - 1] = null;
                count--;
                return result;
            }
        }
        private int Find(object target)
        {
            for (int i = 0; i < count; i++)
            {
                if (contents[i].Equals(target))
                    return i;
            }
            return -1;
        }
        public IBag Union(IBag bag)
        {
            ArrayBag both = new ArrayBag();
            for (int index = 0; index < count; index++)
            {
                both.Add(contents[index]);
            }
            foreach (object o in bag)
            {
                both.Add(o);
            }
            return both;
        }
        public bool Contains(object target)
        {
            if (Find(target) != -1)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        public IEnumerator GetEnumerator()
        {
            for (int index = 0; index < count; index++)
            {
                yield return contents[index];
            }
        }
        #endregion
        public override string ToString()
        {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < count; i++)
            {
                sb.Append(contents[i] + " ");
            }
            return sb.ToString();
        }
    }
 

基于鏈表的集合實現

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public class LinkNode  
   {  
       object element;  
       public object Element  
       {  
           get { return element; }  
           set { element = value; }  
       }  
       LinkNode next;  
       public LinkNode Next  
       {  
           get { return next; }  
           set { next = value; }  
       }  
       public LinkNode(object element)  
       {  
           this.element = element;  
           next = null;  
       }  
       public LinkNode()  
       {  
       }  
   }  
   public class LinkedBag:IBag  
   { 
       #region IBag 成員  
       LinkNode contents;  
       int count;  
       Random r = new Random();  
       public void Add(object element)  
       {  
           LinkNode node = new LinkNode(element);  
           node.Next = contents;  
           contents = node;  
           count++;  
       }  
       public void AddAll(IBag bag)  
       {  
           foreach (object o in bag)  
           {  
               Add(o);  
           }  
       }  
       public int Size  
       {  
           get { return count; }  
       }  
       public bool IsEmpty()  
       {  
           return (count==0);  
       }  
       public object RemoveRandom()  
       {  
           object result = null;  
           LinkNode previous, current;  
           if (IsEmpty())  
           {  
               throw new Exception("collection is empty!");  
           }  
           int choice = r.Next(count);  
           if (choice == 0)  
           {  
               result = contents.Element;  
               contents = contents.Next;  
           }  
           else 
           {  
               previous = contents;  
               for (int i = 1; i < choice; i++)  
               {  
                   previous = previous.Next;  
               }  
               current = previous.Next;  
               result = current.Element;  
               previous.Next = current.Next;  
           }  
           count--;  
           return result;  
       }  
       public object Remove(object target)  
       {  
           bool found = false;  
           LinkNode previous, current;  
           object result = null;  
           if (IsEmpty())  
           {  
               throw new Exception("collection is empty!");  
           }  
           if (contents.Element.Equals(target))  
           {  
               result = contents.Element;  
               contents = contents.Next;  
           }  
           else 
           {  
               previous = contents;  
               current = previous.Next;  
               for(int i=1;i<count&&!found;i++)  
               {  
                   if (current.Element.Equals(target))  
                   {  
                       found = true;  
                   }  
                   previous = current;  
                   current = previous.Next;  
               }  
                 if (!found)  
               {  
                   throw new Exception("Elements not found!");  
               }  
               result = current.Next;  
               previous.Next = current.Next;  
           }  
           count--;  
           return result;  
       }  
       public IBag Union(IBag bag)  
       {  
           LinkedBag both = new LinkedBag();  
           foreach (LinkNode node in this)  
           {  
               both.Add(node.Element);  
           }  
           foreach (LinkNode node in bag)  
           {  
               both.Add(node.Element);  
           }  
           return both;  
       }  
       public bool Contains(object target)  
       {  
           bool found = false;  
           LinkNode current = contents;  
           while (current != null && !found)  
           {  
               if (current.Element.Equals(target))  
               {  
                   found = true;  
               }  
               current = current.Next;  
           }  
           return found;  
       } 
       #endregion 
       #region IEnumerable 成員  
       public System.Collections.IEnumerator GetEnumerator()  
       {  
           LinkNode current = contents;  
           while (current != null)  
           {  
               yield return current;  
               current = current.Next;  
           }  
       } 
       #endregion  
       public override string ToString()  
       {  
           StringBuilder sb = new StringBuilder();  
           foreach (LinkNode node in this)  
               sb.Append(node.Element.ToString() + " ");  
           return sb.ToString();  
       }  
   }