单链表的局限
单链表可以用于表示任意的线性关系，但有些线性关系是循环的，即没有队尾元素的
循环链表的定义
将单链表中最后一个数据元素的next指针指向第一个元素
循环链表的操作
- 创建链表
- 销毁链表
- 获取链表长度
- 清空链表
- 获取第pos个元素操作
- 插入元素到位置pos
- 删除位置pos处的元素
游标的定义
在循环链表中可以定义一个“当前”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的所有元素。
循环链表的新操作
- 获取当前游标指向的数据元素
- 将游标重置指向链表中的第一个数据元素
- 将游标移动指向到链表中的下一个数据元素
- 直接指定删除链表中的某个数据元素
CircleListNode* CircleList_DeleteNode(CircleList* list,CircleListNode* node);
CircleListNode* CircleList_Reset(CircleList* list);
CircleListNode* CircleList_Current(CircleList* list);
CircleListNode* CircleList_Next(CircleList* list);
完整代码
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_Destroy(CircleList* list);
void CircleList_Clear(CircleList* list);
int CircleList_Length(CircleList* list);
int CircleList_Insert(CircleList* list, CircleListNode* node, int pos);
CircleListNode* CircleList_Get(CircleList* list, int pos);
CircleListNode* CircleList_Delete(CircleList* list, int pos);
CircleListNode* CircleList_DeleteNode(CircleList* list,CircleListNode* node);
CircleListNode* CircleList_Reset(CircleList* list);
CircleListNode* CircleList_Current(CircleList* list);
CircleListNode* CircleList_Next(CircleList* list);
#endif
CircleList.c
#include <stdio.h>
#include <malloc.h>
#include "CircleList.h"
typedef struct _tag_CircleList
{
CircleListNode header;
CircleListNode* slider;
int length;
} TCircleList;
CircleList* CircleList_Create()
{
TCircleList* ret = (TCircleList*)malloc(sizeof(TCircleList));
if( ret != NULL )
{
ret->length = 0;
ret->header.next = NULL;
ret->slider = NULL;
}
return ret;
}
void CircleList_Destroy(CircleList* list)
{
free(list);
}
void CircleList_Clear(CircleList* list)
{
TCircleList* sList = (TCircleList*)list;
if( sList != NULL )
{
sList->length = 0;
sList->header.next = NULL;
sList->slider = NULL;
}
}
int CircleList_Length(CircleList* list)
{
TCircleList* sList = (TCircleList*)list;
int ret = -1;
if( sList != NULL )
{
ret = sList->length;
}
return ret;
}
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;
if(sList->length == 0)
{
sList->slider = node;
node->next = node;
}
sList->length++;
}
return ret;
}
CircleListNode* CircleList_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;
}
CircleListNode* CircleList_Delete(CircleList* list, int pos)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
int i = 0;
if( (sList != NULL) && (0 <= pos) )
{
CircleListNode* current = (CircleListNode*)sList;
CircleListNode* first = sList->header.next;
CircleListNode* last = (CircleListNode*)CircleList_Get(sList, sList->length-1);
for(i=0; i<pos; i++)
{
current = current->next;
}
ret = current->next;
current->next = ret->next;
sList->length--;
if(first == ret)
{
sList->header.next = ret->next;
last->next = ret->next;
}
if(sList->slider == ret)
{
sList->slider = ret->next;
}
if(sList->length == 0)
{
sList->header.next = NULL;
sList->slider = NULL;
}
}
return ret;
}
CircleListNode* CircleList_DeleteNode(CircleList* list,CircleListNode* node)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
int i = 0;
if(sList != NULL)
{
CircleListNode* current = (CircleListNode*)sList;
for(i=0; i<sList->length; i++)
{
if(current->next == node)
{
ret = current->next;
break;
}
current = current->next;
}
if(ret != NULL)
{
CircleList_Delete(sList, i);
}
}
return ret;
}
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;
}
CircleListNode* CircleList_Current(CircleList* list)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
if(sList != NULL)
{
ret = sList->slider;
}
return ret;
}
CircleListNode* CircleList_Next(CircleList* list)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
if((sList != NULL)&&(sList->slider != NULL))
{
ret = sList->slider;
sList->slider = ret->next;
}
return ret;
}
main.c
#include <stdio.h>
#include <stdlib.h>
#include "CircleList.h"
struct Value
{
CircleListNode header;
int v;
};
int main(int argc, char *argv[])
{
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)+1);
CircleList_Delete(list, 0);
for(i=0; i<2*CircleList_Length(list); i++)
{
struct Value* pv = (struct Value*)CircleList_Get(list, i);
printf("%d\n", pv->v);
}
printf("\n");
while(CircleList_Length(list) > 0)
{
struct Value* pv = (struct Value*)CircleList_Delete(list, 0);
printf("%d\n", pv->v);
}
CircleList_Destroy(list);
return 0;
}
约瑟夫问题
n个人围成一个圆圈，首先第1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。
应用代码
main.c
#include <stdio.h>
#include <stdlib.h>
#include "CircleList.h"
typedef struct _tag_Value
{
CircleListNode header;
int v;
}Value;
int main(int argc, char *argv[])
{
int i = 0;
int n = 0;
int m = 0;
printf("Please enter: n,m\n");
scanf("%d,%d",&n,&m);
Value* v = (Value*)malloc(sizeof(Value)*n);
CircleList* list = CircleList_Create();
for(i=0;i<n;i++)
{
v[i].v=i+1;
CircleList_Insert(list, (CircleListNode*)&v[i], CircleList_Length(list));
}
for(i=0; i<CircleList_Length(list); i++)
{
Value* pv = (Value*)CircleList_Next(list);
printf("%d\n", pv->v);
}
printf("\n");
CircleList_Reset(list);
while(CircleList_Length(list)>0)
{
Value* pv = NULL;
for(i=1;i<m;i++)
{
CircleList_Next(list);
}
pv = (Value*)CircleList_Current(list);
printf("%d\n", pv->v);
CircleList_DeleteNode(list, (CircleListNode*)pv);
}
CircleList_Destroy(list);
return 0;
}
小结
- 循环链表只是在单链表的基础上做了一个加强
- 循环链表完全可以取代单链表的使用
- 循环链表的Next和Current操作可以高效的遍历链表中的所有元素
