看数据结构写代码（6）双向链表的实现

双向链表 只是 比 单链表 多了 一个 指向 前驱的 指针，在插入 和 删除 元素的 时候 得多处理一些。其余 没什么 区别。

而循环链表 的 尾指针 不再 指向 NULL，而是 指向 头指针，这样 既可以循环遍历，又节省 存储空间 。

每种链表 都有 好处，至于 如何 取舍，得看需求。

下面 奉上 双向链表的实现代码：

// DoubleLinkList.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <stdlib.h>

typedef int Elelment;

enum E_STATE
{
	E_STATE_ERROR = 0,
	E_STATE_Ok = 1,
};

//双链表
struct DoubleList
{
	Elelment data;
	DoubleList * pre;
	DoubleList * next;
};

E_STATE listInit(DoubleList & list){
	list.next = NULL;
	list.pre = NULL;
	return E_STATE_Ok;
}

E_STATE listDestory(DoubleList & list){
	DoubleList * next = list.next;
	while (next)
	{
		DoubleList * freeNode = next;
		next = next->next;
		free(freeNode);
	}
	list.next = NULL;
	return E_STATE_Ok;
}

bool listEmpty(DoubleList  list){
	return list.next == NULL ? true : false;
}

int listLen(DoubleList list){
	int len = 0;
	DoubleList * next = list.next;
	while (next)
	{
		next = next->next;
		len ++;
	}
	return len;
}

E_STATE listGetElement(DoubleList list,int index,DoubleList & listElement){
	int times = 1;
	DoubleList * next = list.next;
	while (next && times < index)
	{
		next = next->next;
		times ++;
	}
	if (next == NULL || times > index)
	{
		return E_STATE_ERROR;
	}
	listElement = *next;
	return E_STATE_Ok;
}

DoubleList * listLocate(DoubleList  list,Elelment e){
	DoubleList * next = list.next;
	while (next)
	{
		if (next->data == e)
		{
			return next;
		}
		next = next->next;
	}
	return NULL;
}

DoubleList * listPreElement(DoubleList  list,Elelment e){
	DoubleList * pLocate = listLocate(list,e);
	return pLocate ? pLocate->pre:NULL;
}

DoubleList * listNextElement(DoubleList  list,Elelment e){
	DoubleList * pLocate = listLocate(list,e);
	return pLocate ? pLocate->next : NULL;
}

E_STATE listInsert(DoubleList & list,int index ,Elelment e){
	DoubleList * pre = &list;//前驱
	int times = 0;
	while (pre && times < index - 1)
	{
		pre = pre ->next;
		times ++;
	}
	if (pre == NULL || times > index - 1)
	{
		return E_STATE_ERROR;
	}
	DoubleList * newNode = (DoubleList *)malloc(sizeof(DoubleList));
	newNode->pre = pre;
	newNode->next = pre->next;
	newNode->data = e;
	if (pre->next)//必须后继不为空
	{
		//后继节点的前驱
		pre->next->pre = newNode;
	}
	pre->next = newNode;
	return E_STATE_Ok;

}

E_STATE listDelete(DoubleList & list,int index){
	DoubleList * next = list.next;
	int times = 1;
	while (times < index && next)
	{
		next = next->next;
		times++;
	}
	if (times > index || next == NULL)
	{
		return E_STATE_ERROR;
	}
	next->pre->next = next->next;
	if (next->next)
	{
		next->next->pre = next->pre;
	}
	free(next);
	return E_STATE_Ok;
}

void listTraverse(DoubleList list){
	DoubleList * next = list.next;
	printf("-------------------\n");
	while (next)
	{
		printf("%d\n",next->data);
		next = next->next;
	}
	printf("-------------------\n");
}

int _tmain(int argc, _TCHAR* argv[])
{
	DoubleList list;
	//初始化
	listInit(list);
	for (int i = 1; i < 11; i++)
	{
		listInsert(list,i,i);
	}
	listTraverse(list);
	//插入，删除测试
	listDelete(list,1);
	listDelete(list,listLen(list));
	listInsert(list,listLen(list),111);
	listInsert(list,listLen(list)+1,222);
	listTraverse(list);
	//其他函数测试.
	printf("表长为：%d\n",listLen(list));
	DoubleList eList;
	listGetElement(list,5,eList);
	printf("第五个节点值为：%d\n",eList.data);
	printf("前驱值为：%d\n",eList.pre->data);
	printf("后继值为：%d\n",eList.next->data);
	return 0;
}