循环链表

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一、单链表的局限

1.单链表可以用于表示任意的线性关系

2.有些关系是循环的即没有头和尾

二、循环链表的定义

将单链表中的最后一个元素的next指针指向第一个元素

三、循环链表中游标的定义

在循环链表中可以定义一个“当前”的指针，这个指针通常称为游标，可以通过这个游标来遍历链表中所有的元素。

三、循环链表的操作(比单链表多的函数操作)

1.获取当前游标指向的数据元素

2.将游标重置指向数据链表的第一个元素

3.将游标重置指向到链表中的下一个数据元素

4.直接删除链表中的某个数据元素

CircleListNode* CircleList_DeleteNode(CircleList* list, CircleListNode* node);  //可以直接删除数据元素而不用知道数据元素的下标

 CircleListNode* CircleList_Reset(CircleList* list);

 CircleListNode* CircleList_Current(CircleList* list);

 CircleListNode* CircleList_Next(CircleList* list);

四、循环链表的应用

约瑟夫问题：

N个人从 1 开始一个人一个人顺时针报数，报到第 m 个人，令其出列。然后再从下一个人开始从 1 顺时针报数，报到第 m 个人，再令其出列，…，如此下去，求出列顺序。

五、循环链表的代码

CircleList.h

#ifndef _CIRCLELIST_H_
#define _CIRCLELIST_H_
 
typedef void CircleList;
 
typedef struct _tag_CircleListNode CircleListNode;
 
struct  _tag_CircleListNode
{
 
CircleListNode* next;
};
 
CircleList* CircleList_Create();
 
void CircleList_DestoryCircleList* list);
 
void CircleList_Clear(CircleList* list);
 
int CircleList_length(CircleList* list);
 
int CircleList_Insert(CircleList* list, CircleListNode* node, int pos);
 
CircleListNode* Circle_Get(CircleList* list,int pos);
 
CircleListNode* Circle_Delete(CircleList* list,int pos);
 
 
/**************************循环链表比单链表多的操作***********************/
 
/*通过游标直接删掉循环链表中的一个元素*/
CircleListNode* CircleList_DeleteNode(CircleList* list, CircleListNode* node);  //可以直接删除数据元素而不用知道数据元素的下标   
/*将循环链表中的游标指向第一个元素*/
CircleListNode* CircleList_Reset(CircleList* list);
/*当前游标指向的元素*/
CircleListNode* CircleList_Current(CircleList* list);
/*移动游标*/
CircleListNode* CircleList_Next(CircleList* list);
 
#endif

CircleList.c

#include<stdio.h>
#include<malloc.h>
#include"CircleList.h"
 
/*头结点的结构*/
typedef struct _tag_CircleList
{
CircleListNode header;
CircleListNode* slider;/*定义游标,游标的默认初始位置应该为第一个元素*/
int length;
}TCircleList;
 
/*循环链表的创建*/
CircleList* CircleList_Create()
{
TCircleList* ret = (TCircleList*)malloc(sizeof(TCircleList));
if (ret != NULL)
{
ret->header.next = NULL;
ret->slider = NULL;  //链表中无元素，游标为空,
ret->length = 0;
}
 
return ret;
}
/*销毁创建的循环链表*/
void CircleList_Destory(CircleList* list)
{
free(list);
}
/*清空循环链表*/
void CircleList_Clear(CircleList* list)
{
TCircleList* slist = (TCircleList*)list;
if (slist != NULL)
{
slist->header.next = NULL;
slist->slider = NULL;
slist->length = 0;
}
 
}
/*得到循环链表的长度*/
 
int CircleList_length(CircleList* list)
{
TCircleList* slist = (TCircleList*)list;
int ret = -1;
if (slist != NULL)
{
ret = slist->length;
}
       return ret;
 
}
 
/*向循环链表中插入一个元素*/  //O(n)
int CircleList_Insert(CircleList* list, CircleListNode* node, int pos)
{
TCircleList* slist = (TCircleList*)list;
int ret = (slist != NULL) && (pos >= 0) && (node != NULL);
int i = 0;
if (ret)
{
CircleListNode* current = (CircleListNode*)slist;
for (i = 0; (i < pos) && (current->next!=NULL); i++)
{
current = current->next;
}
node->next = current->next;
current->next = node;
/*如果插入的元素是第一个,将新插入的元素next指针指向自己*/
if (slist->length == 0)
{
slist->slider = node;  //将游标指向刚插入的第一个结点
node->next = node;
}
slist->length++;
}
return ret;
}
/*取循环链表中的一个元素*/
CircleListNode* Circle_Get(CircleList* list,int pos)
{
TCircleList* slist = (TCircleList*)list;
CircleListNode* ret = NULL;
int i = 0;
if ((slist != NULL) && (0 <= pos))
{
CircleListNode* current = (CircleListNode*)slist;
for (i = 0; i < pos; i++)
{
current = current->next;
}
ret = current->next;
}
return ret;
 
}
/*删除循环链表中的一个元素*/ //O（n）
CircleListNode* Circle_Delete(CircleList* list,int pos)
{
TCircleList* slist = (TCircleList*)list;
int i = 0;
CircleListNode* ret = NULL;
if ((slist != NULL) && (pos >= 0))
{
CircleListNode* current = (CircleListNode*)slist;
/*用来标记第一个元素*/
CircleListNode* first = slist->header.next;
/*用来标记最后一个元素*/
CircleListNode* last = (CircleListNode*)(Circle_Get(slist,slist->length-1));
for (i = 0; i < pos; i++)
{
current->next = current;
}
ret = current->next;
current->next = ret->next;
slist->length--;
/*如果删除的是第一个元素*/
if (first = ret)
{
slist->header.next = ret->next;
last->next = ret->next;
}
 
/*如果删除的元素正好是游标指向的元素*/
if (slist->slider == ret)
{ 
/*将游标指向要删除元素的下一个元素*/
slist->slider = ret->next;
 
}
/*判断链表是否为空*/
if (slist->length == 0)
{ 
/*将表头置为空*/
slist->header.next = NULL;
/*游标设置为空*/
slist->slider = NULL;
}
}
return ret;
}
/*通过游标直接删掉CircleList_DeleteNode循环链表中的一个元素*/  //O(n)
CircleListNode* CircleList_DeleteNode(CircleList* list, CircleListNode* node)
{
TCircleList* slist = (TCircleList*)list;
int i = 0;
CircleListNode* ret = NULL;
if (slist != NULL)
{      
  /*使current指向链表的头*/
      CircleListNode* current = (CircleListNode*)slist;
 /*查找node在循环链表中的逻辑位置*/
for (i = 0; i < slist->length; i++)
{
 /*如果找到node元素，则i为node元素的逻辑位置*/
if (current->next == node)
{
ret = current->next;
break;
}
/*将链表指向下一个元素*/
     current = current->next;
}
/*ret不为空说明找到该元素，将该元素删除*/
if (ret != NULL)
{
Circle_Delete(slist, i);
}
}
 
return ret;
 
}
/*将循环链表中的游标指向第一个元素*///O(1)
CircleListNode* CircleList_Reset(CircleList* list)
{
TCircleList* slist = (TCircleList*)list;
CircleListNode* ret = NULL;
if (slist != NULL)
{
slist->slider = slist->header.next;
ret = slist->slider;
}
return ret;
}
/*当前游标指向的元素*/ //O(1)
CircleListNode* CircleList_Current(CircleList* list)
{
TCircleList* slist = (TCircleList*)list;
CircleListNode* ret = NULL;
if (slist != NULL)
{
ret = slist->slider;
}
return ret;
 
}
/*移动游标*/
CircleListNode* CircleList_Next(CircleList* list)
{
TCircleList* slist = (TCircleList*)list;
CircleListNode* ret = NULL;
/*判断链表和游标是否为空*/
if ((slist != NULL)&&(slist->slider!=NULL))
{
ret = slist->slider;
slist->slider = ret->next;
}
return ret;
}

main.c

#include<stdio.h>
#include"Circlelist.h"
 
struct Value
{
CircleListNode  header;
int v;
};
 
int main()
{
int i = 0;
 
CircleList* list = CircleList_Create();
 
struct Value V1;
struct Value V2;
struct Value V3;
struct Value V4;
struct Value V5;
struct Value V6;
struct Value V7;
struct Value V8;
V1.v = 1;
V2.v = 2;
V3.v = 3;
V4.v = 4;
V5.v = 5;
V6.v = 6;
V7.v = 7;
V8.v = 8;
CircleList_Insert(list,(CircleListNode*)&V1,CircleList_length(list));
CircleList_Insert(list,(CircleListNode*)&V2,CircleList_length(list));
CircleList_Insert(list,(CircleListNode*)&V3,CircleList_length(list));
CircleList_Insert(list,(CircleListNode*)&V4,CircleList_length(list));
//CircleList_Insert(list,(CircleListNode*)&V5,CircleList_length(list));
 
    //Circle_Delete(list, 0);
   CircleList_Insert(list, (CircleListNode*)&V5, 5);
 
for (i = 0; i <2*CircleList_length(list); i++)
{
struct Value* V = (struct Value*) Circle_Get(list, i);
 
printf("%d\n",V->v);
}
  printf("\n");
 
while (CircleList_length(list) > 0)
{
struct Value *pv = (struct Value*)Circle_Delete(list, 0);
printf("%d\n", pv->v);
 
}
    printf("\n");
 
/*以下为约瑟夫问题的解决*/
 
CircleList_Insert(list, (CircleListNode*)&V1, CircleList_length(list));
CircleList_Insert(list, (CircleListNode*)&V2, CircleList_length(list));
CircleList_Insert(list, (CircleListNode*)&V3, CircleList_length(list));
CircleList_Insert(list, (CircleListNode*)&V4, CircleList_length(list));
CircleList_Insert(list, (CircleListNode*)&V5, CircleList_length(list));
CircleList_Insert(list, (CircleListNode*)&V6, CircleList_length(list));
CircleList_Insert(list, (CircleListNode*)&V7, CircleList_length(list));
CircleList_Insert(list, (CircleListNode*)&V8, CircleList_length(list));
for (i = 0; i <CircleList_length(list); i++)
{
struct Value* V = (struct Value*) CircleList_Next(list);
 
printf("%d\n", V->v);
}
 
CircleList_Reset(list);//?
 while (CircleList_length(list) > 0)
 {
 struct Value* pv = NULL;
 for (i = 0; i < 3; i++)
 { 
 CircleList_Next(list);
 }
 pv = (struct Value*) CircleList_Current(list);
 printf("%d\n",pv->v);
 CircleList_DeleteNode(list,(CircleListNode*)pv); 
 }
 
     CircleList_Destory(list);
 
 return 0;
}

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