🧑💻作者: @情话0.0
📝专栏:《数据结构》
👦个人简介:一名双非编程菜鸟,在这里分享自己的编程学习笔记,欢迎大家的指正与点赞,谢谢!
上篇博客带大家认识了单链表,单链表结点中只有一个指向其后继的指针,使得单链表只能从头结点依次向后遍历。对于插入、删除操作得从头遍历,尤其是在链表尾部,还有一点就是无法一步的访问到某个节点的前驱节点,也就是说访问前驱节点的时间复杂度为O(n)。为了避免这样的缺点,便引出了双向循环链表
首先,它是一个链表,通过指针将所有的结点连接在一起;其次,循环链表表示整个链表从头到尾构成一个环,链表尾结点的next
指针指向头结点;再者,双向表示链表结点有两个指针prev和next,分别指向其前驱结点和后继节点;最后,带头结点表示链表的第一个有效结点前附加一个结点,头结点的数值域不设任何信息。带头结点的双向循环链表如下图所示:
看似带头结点的双向循环链表的结构更为复杂,但是对于之前单链表的尾插尾删操作更为简单。
注意: 该链表带头结点,所以在进行任何的插入删除操作都无需传二级指针,因为对于头指针的指向并不会改变,只会改变链表的结点结构体本身。但是在销毁操作下,就必须传二级指针,因为销毁操作是将头结点也要删除掉,也就意味着会改变头指针的指向。
typedef int DHCListNode; //每个结点的数值类型为 int
typedef struct DHCList
{
DHCListNode data;
struct DHCList* prev; //前驱指针
struct DHCList* next; //后继指针
}DHCList;
DHCList* BuyDHCListNode(DHCListNode data)
{
DHCList* newNode = (DHCList*)malloc(sizeof(DHCList));
if (newNode == NULL)
{
return NULL;
}
newNode->data = data;
newNode->next = NULL; //对于没一个刚申请的结点让其前驱指针和后继指针都指向NULL
newNode->prev = NULL;
return newNode;
}
在对链表的任何操作之前得先创建一个头结点,根据双向循环的特性,需让头结点的
prev
和next
指针都指向其自己。
DHCList* ListInit()
{
DHCList* pHead = BuyDHCListNode(0);
if (pHead == NULL)
{
return NULL;
}
pHead->next = pHead;
pHead->prev = pHead;
return pHead;
}
从链表的头结点的后继结点开始逐一匹配,直到找到值相同的结点进行返回,若当查找结点一直后继到头结点时意味着没有该结点,就返回
NULL
DHCList* ListFind(DHCList* pHead, DHCListNode data)
{
assert(pHead);
DHCList* cur = pHead->next;
while (cur != pHead)
{
if (cur->data == data)
{
return cur;
}
cur = cur->next;
}
return NULL;
}
void ListInsert(DHCList* pos, DHCListNode data)
{
assert(pos);
DHCList* newNode = BuyDHCListNode(data);
//以下四步不能混乱,如果先执行了三四步,那么就无法通过pos结点找到newnode结点的前驱结点。
newNode->next = pos;
newNode->prev = pos->prev;
pos->prev->next = newNode;
pos->prev = newNode;
}
void ListErase(DHCList* pos)
{
assert(pos);
pos->prev->next = pos->next;
pos->next->prev = pos->prev;
free(pos);
}
链表的尾删可以用链表
pos
位置插入进行复用,因为链表的插入是在pos
位置之前插入,所以在链表尾插的函数里直接将pos
改为头结点即可。
void ListPushBack(DHCList* pHead, DHCListNode data)
{
assert(pHead);
ListInsert(pHead, data);
}
l链表的尾删同样也可以进行复用,直接将
pos
改为尾结点即可,也就是头结点的前驱节点。
void ListPopBack(DHCList* pHead)
{
assert(pHead);
ListErase(pHead->prev); //头结点的前驱节点(链表尾结点)
}
链表头插即为将待插结点插在头结点之后。
void ListPushFront(DHCList* pHead, DHCListNode data)
{
assert(pHead);
ListInsert(pHead->next, data); //
}
void ListPopBack(DHCList* pHead)
{
assert(pHead);
ListErase(pHead->prev); //删除头结点的后继结点
}
该函数意为将链表中除头结点之外的所有结点都销毁。
void ListClear(DHCList* pHead)
{
assert(pHead);
DHCList* cur = pHead->next;
while (cur != pHead)
{
pHead->next = cur->next;
free(cur);
cur = pHead->next;
}
pHead->next = pHead;
pHead->prev = pHead;
}
void ListDestory(DHCList** pHead) //参数为二级指针
{
assert(pHead);
ListClear(*pHead); //先清空链表,再释放掉头节点即可。
free(*pHead);
*pHead = NULL;
}
结构体创建及函数声明
#include
#include
#include
typedef int DHCListNode;
typedef struct DHCList
{
DHCListNode data;
struct DHCList* prev;
struct DHCList* next;
}DHCList;
DHCList* ListInit();
DHCList* BuyDHCListNode(DHCListNode data);
DHCList* ListFind(DHCList* pHead, DHCListNode data);
void ListPushBack(DHCList* pHead, DHCListNode data);
void ListPushFront(DHCList* pHead, DHCListNode data);
void ListPopBack(DHCList* pHead);
void ListPopFront(DHCList* pHead);
void ListInsert(DHCList* pos, DHCListNode data);
void ListErase(DHCList* pos);
void ListPrint(DHCList* pHead);
void ListClear(DHCList* pHead);
void ListDestory(DHCList** pHead);
void TestList();
方法实现
#include "DCHListNode.h"
DHCList* BuyDHCListNode(DHCListNode data)
{
DHCList* newNode = (DHCList*)malloc(sizeof(DHCList));
if (newNode == NULL)
{
return NULL;
}
newNode->data = data;
newNode->next = NULL;
newNode->prev = NULL;
return newNode;
}
DHCList* ListInit()
{
DHCList* pHead = BuyDHCListNode(0);
if (pHead == NULL)
{
return NULL;
}
pHead->next = pHead;
pHead->prev = pHead;
return pHead;
}
DHCList* ListFind(DHCList* pHead, DHCListNode data)
{
assert(pHead);
DHCList* cur = pHead->next;
while (cur != pHead)
{
if (cur->data == data)
{
return cur;
}
cur = cur->next;
}
return NULL;
}
void ListPushBack(DHCList* pHead, DHCListNode data)
{
assert(pHead);
ListInsert(pHead, data);
}
void ListPushFront(DHCList* pHead, DHCListNode data)
{
assert(pHead);
ListInsert(pHead->next, data);
}
void ListPopBack(DHCList* pHead)
{
assert(pHead);
ListErase(pHead->prev);
}
void ListPopFront(DHCList* pHead)
{
assert(pHead);
ListErase(pHead->next);
}
//在pos之前插入
void ListInsert(DHCList* pos, DHCListNode data)
{
assert(pos);
DHCList* newNode = BuyDHCListNode(data);
newNode->next = pos;
newNode->prev = pos->prev;
pos->prev->next = newNode;
pos->prev = newNode;
}
void ListErase(DHCList* pos)
{
assert(pos);
pos->prev->next = pos->next;
pos->next->prev = pos->prev;
free(pos);
}
void ListPrint(DHCList* pHead)
{
assert(pHead);
DHCList* cur = pHead->next;
while (cur != pHead)
{
printf("%d----", cur->data);
cur = cur->next;
}
printf("NULL\n");
}
void ListClear(DHCList* pHead)
{
assert(pHead);
DHCList* cur = pHead->next;
while (cur != pHead)
{
pHead->next = cur->next;
free(cur);
cur = pHead->next;
}
pHead->next = pHead;
pHead->prev = pHead;
}
void ListDestory(DHCList** pHead)
{
assert(pHead);
ListClear(*pHead);
free(*pHead);
*pHead = NULL;
}
void TestList()
{
DHCList* pHead = ListInit();
ListPushBack(pHead, 1);
ListPushBack(pHead, 2);
ListPushBack(pHead, 3);
ListPushBack(pHead, 4);
ListPrint(pHead);
ListPushFront(pHead, 0);
ListPrint(pHead);
ListPopFront(pHead);
ListPrint(pHead);
ListPopBack(pHead);
ListPrint(pHead);
ListClear(pHead);
ListPrint(pHead);
ListDestory(&pHead);
//ListPrint(pHead);
}
主函数
#include "DCHListNode.h"
int main()
{
TestList();
return 0;
}
带头结点的双向循环链表的结构比较复杂,所以对链表进行插入删除操作时一定要注意指针指向的先后顺序;还有就是传递的参数为一级指针即可,只有在删除链表时才需传二级指针。
文章若有不足的地方还请大佬指正!!!