前言:前面我们实现了顺序表和单链表,这次来实现一个结构更复杂的链表-----带头双向循环链表。不要被它的名字吓到哦,只是结构复杂而已,它的结构更有利于代码的实现。
1 双向循环链表的介绍
有了单链表的基础,要实现这个双向循环带头链表其实并不难。下面我们先来了解一下什么是双向循环带头链表。
这就是双向循环带头链表的结构图,可以很清晰的看到,这个链表需要两个指针,一个指向后继结点,一个指向前驱节点,其次还需要一个头结点。只是这个头结点并不需要存储有效数据。
2 双向循环链表的实现
2.1 双向循环带头链表的定义
c
//存储的数据类型
typedef int LDataType;
//链表的定义
typedef struct ListNode
{
LDataType val;
struct ListNode* next;//指向后继节点
struct ListNode* prev;//指向前驱节点
}LTNode;
2.2 双向循环带头链表的接口
c
//初始化双向循环带头链表'
LTNode* ListInit();
//打印
void ListPrint(plist);
//尾插
void ListPushBack(LTNode* phead, LDataType x);
//尾删
void ListPopBack(LTNode* phead);
//头插
void ListPushFront(LTNode* phead, LDataType x);
//头删
void ListPopFront(LTNode* phead);
//查找
LTNode* ListFind(LTNode* phead, LDataType x);
//pos位置之前插入
void ListInsert(LTNode* pos, LDataType x);
//删除pos位置
void ListErase(LTNode* pos);
//销毁链表
void ListDestroy(LTNode* phead);
2.2.1 初始化链表
c
//初始化双向循环带头链表
LTNode* ListInit()
{
//哨兵位头结点
LTNode* phead = (LTNode*)malloc(sizeof(LTNode));
if (phead == NULL)
{
printf("malloc fail\n");
exit(-1);
}
phead->next = phead;
phead->prev = phead;
return phead;
}
2.2.2 创建新节点
c
//创建新节点
LTNode* BuyListNode(LDataType x)
{
LTNode* newnode = (LTNode*)malloc(sizeof(LTNode));
if (newnode == NULL)
{
printf("malloc fail\n");
exit(-1);
}
newnode->val = x;
newnode->prev=newnode->next=NULL;
return newnode;
}
2.2.3 链表尾插
c
//尾插
void ListPushBack(LTNode* phead, LDataType x)
{
assert(phead);
LTNode* tail = phead->prev;
/*LTNode* newnode = (LTNode*)malloc(sizeof(LDataType));
if (newnode == NULL)
{
printf("malloc fail\n");
exit(-1);
}
newnode->val = x;*/
LTNode* newnode = BuyListNode(x);
newnode->next = phead;
phead->prev = newnode;
newnode->prev = tail;
tail->next = newnode;
}
通过phead->prev就可以找到链表的尾节点,增加的节点newnode->prev
应该链接链表尾节点,链表的尾节点链接newnode,newnode->next应
该链接链表的头结点,链表的头结点的prev保存newnode的地址,使
newnode成为链表新的尾节点。
2.2.4 链表头插
c
//头插
void ListPushFront(LTNode* phead, LDataType x)
{
assert(phead);
LTNode* newnode = BuyListNode(x);
LTNode* pheadNext = phead->next;
phead->next = newnode;
newnode->prev = phead;
pheadNext->prev = newnode;
newnode->next = pheadNext;
}
先创建一个指针指向头结点的后继结点,再让newnode->next保存该
节点的地址,该节点的prev保存newnode的地址,phead->next保存
newnode的地址,newnode->prev保存头结点的地址。
2.2.5 链表尾删
c
//尾删
void ListPopBack(LTNode* phead)
{
assert(phead);
assert(phead->next != phead);
LTNode* tail = phead->prev;
LTNode* tailPrev = tail->prev;
tailPrev->next = phead;
phead->prev = tailPrev;
free(tail);
}
通过phead->prev找到链表尾节点,再通过尾节点的prev找到尾节点
的前驱节点,让该前驱节点的next指向phead,phead->prev指向该前
驱节点,最后释放尾节点。
2.2.6 链表头删
c
//头删
void ListPopFront(LTNode* phead)
{
assert(phead);
assert(phead->next != phead);
LTNode* head = phead->next;
LTNode* next = head->next;
next->prev = phead;
phead->next = next;
free(head);
}
首先通过phead->next找到链表头结点的后继结点,再通过该后继结点找到下一个节点,使该节点的prev保存头结点的地址,头结点的next保存该节点的地址,最后释放该后继结点。
2.2.7 链表的查找
c
//查找
LTNode* ListFind(LTNode* phead, LDataType x)
{
assert(phead);
LTNode* cur = phead->next;
while (cur != phead)
{
if (cur->val == x)
{
return cur;
}
else
{
cur = cur->next;
}
}
return NULL;
}
从头结点的后继结点开始遍历查找,找到了就返回该节点的地址,找不到返回NULL(当再一次遍历到头结点时,说明未找到)。
2.2.8 从pos位置之前插入
c
//pos位置之前插入
void ListInsert(LTNode* pos, LDataType x)
{
assert(pos != NULL);
LTNode* newnode = BuyListNode(x);
LTNode* posPrev = pos->prev;
posPrev->next = newnode;
newnode->prev = posPrev;
newnode->next = pos;
pos->prev = newnode;
}
首先找到pos位置的前驱节点,再让newnode->prev指向该前驱节
点,该前驱节点的next指向newnode,pos->prev指newnode,
newnode->next指向pos。
2.2.9 删除pos位置
c
//删除pos位置
void ListErase(LTNode* pos)
{
assert(pos != NULL);
LTNode* posPrev = pos->prev;
LTNode* posNext = pos->next;
posPrev->next = posNext;
posNext->prev = posPrev;
free(pos);
}
找到pos位置的前驱节点和后继结点,让该前驱节点的next指向该后
继结点,该后继结点的prev指向该前驱节点。
2.2.10 链表的打印
c
//打印
void ListPrint(LTNode* phead)
{
assert(phead);
LTNode* cur = phead->next;
while (cur != phead)
{
printf("%d ", cur->val);
cur = cur->next;
}
printf("\n");
}
从头结点的后继结点开始遍历链表,当节点不是头结点时就打印该节点的值。
2.2.11 销毁链表
c
//销毁链表
void ListDestroy(LTNode* phead)
{
assert(phead);
LTNode* cur = phead->next;
while (cur != phead)
{
LTNode* tmp = cur;
cur = cur->next;
free(tmp);
tmp = NULL;
}
cur = NULL;
phead = NULL;
}
从头结点的后继结点开始销毁,先记录该后继结点的下一个节点,再销毁该后继结点。重复上述操作,直到再一次回到头结点的位置,此时销毁该头结点。
3 完整代码的实现
List.h文件
c
#pragma once
#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
typedef int LDataType;
typedef struct ListNode
{
LDataType val;
struct ListNode* next;
struct ListNode* prev;
}LTNode;
//初始化双向循环带头链表'
LTNode* ListInit();
//打印
void ListPrint(plist);
//尾插
void ListPushBack(LTNode* phead, LDataType x);
//尾删
void ListPopBack(LTNode* phead);
//头插
void ListPushFront(LTNode* phead, LDataType x);
//头删
void ListPopFront(LTNode* phead);
//查找
LTNode* ListFind(LTNode* phead, LDataType x);
//pos位置之前插入
void ListInsert(LTNode* pos, LDataType x);
//删除pos位置
void ListErase(LTNode* pos);
//销毁链表
void ListDestroy(LTNode* phead);
List.c文件
c
#define _CRT_SECURE_NO_WARNINGS
#include"List.h"
//初始化双向循环带头链表
LTNode* ListInit()
{
//哨兵位头结点
LTNode* phead = (LTNode*)malloc(sizeof(LTNode));
if (phead == NULL)
{
printf("malloc fail\n");
exit(-1);
}
phead->next = phead;
phead->prev = phead;
return phead;
}
//打印
void ListPrint(LTNode* phead)
{
assert(phead);
LTNode* cur = phead->next;
while (cur != phead)
{
printf("%d ", cur->val);
cur = cur->next;
}
printf("\n");
}
//销毁链表
void ListDestroy(LTNode* phead)
{
assert(phead);
LTNode* cur = phead->next;
while (cur != phead)
{
LTNode* tmp = cur;
cur = cur->next;
free(tmp);
tmp = NULL;
}
cur = NULL;
phead = NULL;
}
//创建新节点
LTNode* BuyListNode(LDataType x)
{
LTNode* newnode = (LTNode*)malloc(sizeof(LTNode));
if (newnode == NULL)
{
printf("malloc fail\n");
exit(-1);
}
newnode->val = x;
//newnode->prev = newnode->next = NULL;
return newnode;
}
//尾插
void ListPushBack(LTNode* phead, LDataType x)
{
assert(phead);
LTNode* tail = phead->prev;
/*LTNode* newnode = (LTNode*)malloc(sizeof(LDataType));
if (newnode == NULL)
{
printf("malloc fail\n");
exit(-1);
}
newnode->val = x;*/
LTNode* newnode = BuyListNode(x);
newnode->next = phead;
phead->prev = newnode;
newnode->prev = tail;
tail->next = newnode;
}
//尾删
void ListPopBack(LTNode* phead)
{
assert(phead);
assert(phead->next != phead);
LTNode* tail = phead->prev;
LTNode* tailPrev = tail->prev;
//free(tail);
tailPrev->next = phead;
phead->prev = tailPrev;
free(tail);
}
//头插
void ListPushFront(LTNode* phead, LDataType x)
{
assert(phead);
LTNode* newnode = BuyListNode(x);
LTNode* pheadNext = phead->next;
phead->next = newnode;
newnode->prev = phead;
pheadNext->prev = newnode;
newnode->next = pheadNext;
}
//头删
void ListPopFront(LTNode* phead)
{
assert(phead);
assert(phead->next != phead);
LTNode* head = phead->next;
LTNode* next = head->next;
next->prev = phead;
phead->next = next;
free(head);
}
//查找
LTNode* ListFind(LTNode* phead, LDataType x)
{
assert(phead);
LTNode* cur = phead->next;
while (cur != phead)
{
if (cur->val == x)
{
return cur;
}
else
{
cur = cur->next;
}
}
return NULL;
}
//pos位置之前插入
void ListInsert(LTNode* pos, LDataType x)
{
assert(pos != NULL);
LTNode* newnode = BuyListNode(x);
LTNode* posPrev = pos->prev;
posPrev->next = newnode;
newnode->prev = posPrev;
newnode->next = pos;
pos->prev = newnode;
}
//删除pos位置
void ListErase(LTNode* pos)
{
assert(pos != NULL);
LTNode* posPrev = pos->prev;
LTNode* posNext = pos->next;
posPrev->next = posNext;
posNext->prev = posPrev;
free(pos);
}
test.c文件
c
#define _CRT_SECURE_NO_WARNINGS
#include"List.h"
void ListTest1()
{
LTNode* plist = ListInit();
ListPushBack(plist, 1);
ListPushBack(plist, 2);
ListPushBack(plist, 3);
ListPushBack(plist, 4);
ListPushBack(plist, 5);
ListPrint(plist);
ListPopBack(plist);
ListPopBack(plist);
ListPrint(plist);
ListPushFront(plist, 6);
ListPushFront(plist, 7);
ListPushFront(plist, 8);
ListPushFront(plist, 9);
ListPushFront(plist, 10);
ListPrint(plist);
ListPopFront(plist);
ListPopFront(plist);
ListPopFront(plist);
ListPrint(plist);
LTNode* pos = ListFind(plist, 2);
if (NULL != pos)
{
printf("找到了\n");
}
else
{
printf("找不到\n");
}
ListInsert(pos, 10);
ListPrint(plist);
pos = ListFind(plist, 1);
ListErase(pos);
ListPrint(plist);
ListDestroy(plist);
plist = NULL;
//ListPrint(plist);
}
int main()
{
ListTest1();
return 0;
}