(二)双链表的构造及相关操作

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上一篇写了单链表，双链表在此基础上增加了一些操作。对于求表长度和查找，与单链表基本相同。插入和删除需要修改的指针增多。一些比较特殊位置的操作，如最后一个节点的删除、在最后一个位置插入元素。需要细心。觉得代码还是得多写，写着写着就熟悉了。以下是源码，希望大家多多指点，谢谢！

#include<iostream>
using namespace std;
/**
author:hendery
content:Creat a double linked list and implement the relevent
		operations such as:inserting an element,deleteing an
		element,search an element,getting the length of the
		list,printing the data of all elements and so with it。
time:2012-3-24
*/
struct Node
{
	struct Node *prior;
	int data;
	struct Node *next;
};

Node *CreatDoubleList()//建立双链表
{
	Node *head,*node,*temp;
	head = (Node*)malloc(sizeof(Node));
	head ->next = NULL;
	temp = head;
    
	int i = 1;
	while(true)
	{
		node = (Node*)malloc(sizeof(Node));
		cout<<"输入第"<<i++<<"节点的值"<<endl;
		cin>>node->data;
		if(node->data == -1)
			break;
		temp->next = node;
		node->prior = temp;
		temp = temp->next;
	}
	temp->next = NULL;
	return head;
}

int length(Node *head)
{
	int i = 0;
	Node *node;
	node = head;
	while(node->next!=NULL)
	{
		
		node = node->next;
		i++;
	}
	return i;
}

Node *insertElement(Node *head,int i,int data)//i代表插入的位置,data 为插入值
{
	if(i>length(head)||i<1)//插入的位置不符要求
	{
		cout<<"error!";
		return NULL;
	}
	int j = 0;
	Node *temp;
	temp = head;
	//while(temp&&j<i-1)
	while(j<i-1&&temp)
	{
		
		temp = temp->next;//找到插入节点的位置
		j++;
	}
	Node *node;
	node = (Node*)malloc(sizeof(Node));//为要插入的节点申请空间
	node->next = temp->next;//要插入的节点的后继指向temp的后继
	temp->next->prior = node;//temp的前驱指向node
	temp->next = node;		//temp的后继指向node
	node->prior = temp;		//node的前驱指向temp
	node->data = data;		//写入值
	return head;			//返回修改后的链表头结点

}

Node *deleteElement(Node *head,int i)
{
	if(i>length(head)||i<1)//错误的删除位置
	{
		cout<<"error!"<<endl;
		return NULL;
	}
	int j = 0;
	Node *temp;
	temp = head->next;
	while(j<i-1&&temp)
	{
		j++;
		temp = temp->next;
	}
	/*if(temp->next==NULL)
		free(temp);
	Node *p;
	p=temp->next;
	temp->next=p->next;
	p->next->prior=temp;	
	free(p);*/
	if(temp->next==NULL)
	{
		temp->prior->next=NULL;//此步骤是关键，在删除最后一个节点时，需要将其的                                  prior改为尾节点
		free(temp);

	}
	else
	{
		/*temp为要删除的节点，将temp的prior指向temp的next
		temp的next的prior指向temp->prior
		*/
		temp->prior->next=temp->next;
		temp->next->prior=temp->prior;
		free(temp);
	}
	return head;
}
void search(Node *head,int i)//查找链表第i个元素的值，并输出
{
	int j = 0;
	Node *temp;
	temp = head;
	while((j++)<i&&temp)
	{
		temp=temp->next;
	}
	if(temp==NULL)
	{
		cout<<"位置有误！"<<endl;		
		return;
	}
	cout<<"第"<<i<<"个元素的值为:"<<temp->data<<endl;
}
void print(Node *head)//打印当前链表中的元素
{
	Node *node;
	node = head->next;
	cout<<"当前链表中的元素有："<<endl;
	while(node!=NULL)
	{
		cout<<node->data<<" ";
		node = node->next;	
	}
}
void main()
{
	Node *head;
	head = CreatDoubleList();
	int len;
	len = length(head);
	cout<<"length of list is:"<<len<<endl;
	print(head);

	int location,data;
	cout<<"输入要插入节点的位置和值"<<endl;
	cout<<"位置：";
	cin>>location;
	cout<<"值：";
	cin>>data;
	insertElement(head,location,data);
	print(head);

	int i;
	cout<<"输入要删除节点的位置"<<endl;
	cin>>i;
	deleteElement(head,i);
	cout<<"此时链表的长度为："<<length(head)<<endl;
	print(head);

	int s;
	cout<<"输入要查找节点的位置";
	cin>>s;
	search(head,s);
	system("pause");
}