插入到泛型链表

Question

我有一个问题插入一个新的对象到链表。我使用了一个名为Insert的自定义方法，该方法接受对象类型和应该放置对象的索引。然而，当我插入对象时，列表没有更新。知道为什么吗?

列表:

        GenericLinkedList<string> bet = new GenericLinkedList<string>();
        bet.Add("a");
        bet.Add("b");
        bet.Add("c");
        bet.Add("d");
        //bet.Remove();
        bet.Insert("x", 2);

泛型链表类:

public class GenericLinkedList<T> where T : IComparable<T> 
{
    public GenericLinkedList()
    {
        count = 0;
        head = null;
    }
    #region Nested Node Class
    private class Node<T>
    {
        private T data;
        public T Data
        {
            get { return data; }
            set { data = value; }
        }
        private Node<T> next;
        public Node<T> Next
        {
            get { return next; }
            set { next = value; }
        }
        public Node<T> Previous { get; set; }

        public Node(T obj_t)
        {
            next = null;
            data = obj_t;
        }
        public Node()
        {
            next = null;
        }

    }
    #endregion
    private Node<T> head;
    private Node<T> tail;

    private int count;
    public int Count
    {
        get
        {
            int num;
            if (count < 0)
                num = 0;
            else {
                num = count;
            }
            return num;
        }
    }

}

插入方法:

    public void Insert(T data, int index)
    {
        Node<T> replacedItem = new Node<T>();
        Node<T> newItem = new Node<T>(data);
        if (head == null)
        {
            head = new Node<T>(data);
            tail = head;
        }
        else
        {
            Node<T> current = head;
            Node<T> tempNode = new Node<T>();

            if (index > 0 && index <= count + 1)
            {
                int c = 0;
                while (current != null)
                {
                    if (c == index)
                    {
                        tempNode = current;
                        current = newItem;
                        current.Next = tempNode;
                    }
                    else
                    {
                        current = current.Next;
                    }
                    c++;
                }
            }
            count++; 
        }
    }

Add方法:

  public void Add(T data)
    {
        count++;
        if (head == null)
        {
            head = new Node<T>(data);
            tail = head;
        }
        else
        {
            tail.Next = new Node<T>(data);
            tail.Next.Previous = tail;
            tail = tail.Next;
        }
    }

Answer 1

需要在case head为null时添加count++。此外，count++应该放在if(index>0&&index<=count+1)

public void Insert(T data, int index)
{
    Node<T> replacedItem = new Node<T>();
    Node<T> newItem = new Node<T>(data);
    if (head == null)
    {
        head = new Node<T>(data);
        tail = head;
        count++;
    }
    else
    {
        Node<T> current = head;
        Node<T> tempNode = new Node<T>();

        if (index > 0 && index <= count + 1)
        {
            int c = 0;
            while (current != null)
            {
                if (c == index)
                {
                    tempNode = current;
                    current = newItem;
                    current.Next = tempNode;
                }
                else
                {
                    current = current.Next;
                }
                c++;
            }
            count++;
        }             
    }
}

Answer 2

您没有正确地在Insert方法中添加新项
在这个地方

tempNode = current; // save pointer to current item
current = newItem; // save in current new item
current.Next = tempNode; //set next to counter

但是你没有改变前一个元素的链接，所以当你再次从头部开始时，你就会错过你添加的项目。

你需要把这段代码改成

public void Insert(T data, int index)
{
    Node<T> replacedItem = new Node<T>();
    Node<T> newItem = new Node<T>(data);
    if (head == null)
    {
        head = new Node<T>(data);
        tail = head;
        count++;
    }
    else
    {
        Node<T> current = head;
        Node<T> tempNode = new Node<T>();

        if (index > 0 && index <= count + 1)
        {
            int c = 0;
            while (current != null)
            {
                if (c == index)
                {
                    tempNode = current;
                    current = newItem;
                    //update link from previous element
                    if(tempNode.Previous != null) 
                       tempNode.Previous.Next = current;
                    current.Next = tempNode;
                    current.Previous = tempNode.Previous;
                    tempNode.Previous = current;
                    count++;
                    break;
                }
                else
                {
                    current = current.Next;
                }
                c++;
            }
        }             
    }
}