数据结构学习（5）：链表

using  System;

namespace  DataStructure.LinkedList
{
    /**//// <summary>
    /// Class1 的摘要说明。
    /// </summary>
    public class ListNode
    {
        public string airport;
        public ListNode link;
        public ListNode previous;
    }
    public class LinkedList
    {
        public int length;//结点数
        public ListNode firstNode;

        public int size()
        {
            return length;
        }
        
        public void insertNewSecondNode(string airportCode)
        {
            if (length==0) return;
            ListNode newNode;//让newNode成为一个ListNode变量
            newNode=new ListNode();//在newNode中存储一个新结点
            newNode.airport=airportCode;
            newNode.link=firstNode.link;//让newNode连接到L的次结点
            newNode.previous=firstNode;
            firstNode.link=newNode;//让L的第一个结点连接到newNode
            firstNode.previous=null;//
            length++;
        }

        public ListNode listSearch(string airportCode)
        {
            ListNode N;
            N=firstNode;
            while(N!=null)
            {
                if(airportCode.Equals(N.airport))
                {
                    return N;
                }
                else
                    N=N.link;

            }
            return N;
        }

        public void deleteLastNode()
        {
            ListNode previousNode,currentNode;
            if(firstNode!=null)
            {
                if(firstNode.link==null)
                {
                    firstNode=null;
                    length--;
                }
                else
                {
                    previousNode=firstNode;
                    currentNode=firstNode.link;

                    while(currentNode.link!=null)//前移两个指针
                    {
                        previousNode=currentNode;
                        currentNode=currentNode.link;
                    }
                    previousNode.link=null;//把倒数第二个结点指向空
                    length--;
                }
            }
        }
        public void insertNewLastNode(string airportCode)
        {
            ListNode N=new ListNode();//通过airport==airportNode和link==null构造
            N.airport=airportCode;
            N.link=null;
            //将N作为新的末端结点插入
            if(firstNode==null)
                firstNode=N;
            else
            {
                //利用结点指针P定位链表的末端结点
                ListNode P=firstNode;
                while(P.link!=null)
                {
                    P=P.link;
                }

                //最后将结点N链接到末端
                P.link=N;
            }
            length++;
        }
        public void print()
        {
            ListNode N;
            //首先，打印一个左括号
            Console.WriteLine("(");
            N=firstNode;
            //假如N没有指向空结点，则打印的airport
            //并将N前移指向链表的下一个结点
            while(N!=null)
            {
                Console.WriteLine(N.airport);
                N=N.link;
                if(N!=null)
                {
                    Console.WriteLine(",");
                }
            }
            Console.WriteLine(")");
        }

        public void  insertNewFirstNode(string A)
        {
            ListNode N=new ListNode();
            N.airport=A;
            N.link=firstNode;
            N.previous=null;
            firstNode=N;
        }
        public LinkedList Clone()
        {
            LinkedList NL=new LinkedList();
            NL.firstNode=this.firstNode;
            NL.length=this.length;
            return NL;
        }
        public void deleteFirst()
        {
            firstNode=firstNode.link;
        }

        
        public static void Main()
        {
            LinkedList L=new LinkedList();
            L.insertNewLastNode("DUS");
            L.insertNewLastNode("ORD");
            L.insertNewLastNode("SAN");
            
            L.print();
            L.insertNewFirstNode("CHN");
            L.print();
            L.deleteFirst();
            L.print();
            LinkedList NL=L.Clone();
            NL.print();
            Console.WriteLine(L.length);
            Console.ReadLine();
            
        }

        public void reverse()
        {
            firstNode=reverse1(firstNode);
//            Reverse采取下面的辅助方法reverse（L），让LinkedList头结点的firstNode
//            域指向链表L
        }
        public ListNode reverse1(ListNode L)
        {
            if(L==null)
            {
                return null;//基本状态
            }
            else
            {
                ListNode head=L;
                ListNode tail=L.link;//将L划分为head和tail
                head.link=null;//掉转
                return concat(reverse1(tail),head);//递归
            }
        }

        public ListNode concat(ListNode L1,ListNode L2)
        {
            if(L1==null)
                return L2;//基本状态
            else
            {
                L1.link=concat(L1.link,L2);//递归
                return L1;
            }
        }
    }
}