双向链表

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

namespace ConsoleApplication4
{
    class DoubleLinkedList
    {

        private Node head;


        public void Add(int data)
        {
            if (head==null)
            {
                head = new Node(data);
            }
            else
            {
                head=head.Add(new Node(data));
            }

        }

        public override string ToString()
        {
            if (head==null)
            {
                return string.Empty;
            }
            else
            {
                return this.head.ToString();
            }
        }



        public class Node
        {
            //节点的值
            private int data;
            private Node next;
            private Node prev;


            public Node(int data)
            {
                this.data = data;
            }

            public int Data
            {
                get { return this.data; }
            }

            public Node Add(Node newNode)
            {
                if (data > newNode.data) //传进来的值大于当前值
                {
                    newNode.next = this;//把传进来的值放到当前值前面去
                    if (this.prev!=null)//前面不为空
                    {
                        this.prev.next = newNode;
                        newNode.prev = this.prev;
                    }
                    this.prev = newNode;  //设置当前节点的前一个节点为新节点
                    return newNode;//只有新节点为头节点时才返回
                }
                else 
                {
                    if (this.next!=null)
                    {//递归
                        this.next.Add(newNode);
                    }
                    else
                    {
                        this.next = newNode;//设置新节点为当前节点的下一节点
                        newNode.prev = this;
                    }
                    return this;
                }
            }


            public override string ToString()
            {
                string str = data.ToString();
                if (next!=null)
                {
                    str += "        " + next.ToString();
                }
                return str;
            }
        }
    }
}

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

namespace ConsoleApplication4
{
    class Program
    {
        static void Main(string[] args)
        {

            DoubleLinkedList lst = new DoubleLinkedList();

            lst.Add(1);
            lst.Add(3);
            lst.Add(9);
            lst.Add(2);
            lst.Add(6);
            lst.Add(5);
            lst.Add(8);

           Console.WriteLine( (lst.ToString()));


           Console.ReadLine();


        }
    }
}