数据结构-循环链表（学习笔记）

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

游标：

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。

一些新的操作：

1.获取当前游标指向的数据元素

2.将游标重置指向链表中的第一个数据元素

3.将游标移动指向到链表中的下一个数据元素

4.直接指定删除链表中的某个数据元素

头文件:

#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

c文件

#include <stdio.h>
#include <malloc.h>
#include "CircleList.h"

typedef struct _tag_CircleList
{
CircleListNode header;
CircleListNode* slider;
int length;
} TCircleList;

CircleList* CircleList_Create() // O(1)
{
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) // O(1)
{
free(list);
}

void CircleList_Clear(CircleList* list) // O(1)
{
TCircleList* sList = (TCircleList*)list;

if( sList != NULL )
{
sList->length = 0;
sList->header.next = NULL;
sList->slider = NULL;
}
}

int CircleList_Length(CircleList* list) // O(1)
{
TCircleList* sList = (TCircleList*)list;
int ret = -1;

if( sList != NULL )
{
ret = sList->length;
}

return ret;
}

int CircleList_Insert(CircleList* list, CircleListNode* node, int pos) // O(n)
{
TCircleList* sList = (TCircleList*)list;
int ret = (sList != NULL) && (pos >= 0) && (node != NULL);
int i = 0;

if( ret )
{
CircleListNode* current = (CircleListNode*)sList;
//查找pos的元素
for(i=0; (i<pos) && (current->next != NULL); i++)
{
current = current->next;
}
//插入元素
node->next = current->next;
current->next = node;
//如果只有一个元素则自己指向自己
if( sList->length == 0 )
{
sList->slider = node;
node->next = node;
}

sList->length++;
}

return ret;
}

CircleListNode* CircleList_Get(CircleList* list, int pos) // O(n)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
int i = 0;

if( (sList != NULL) && (pos >= 0) )
{
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) // O(n)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
int i = 0;

if( (sList != NULL) && (pos >= 0) )
{
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) // O(n)
{
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) // O(1)
{
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) // O(1)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;

if( sList != NULL )
{
ret = sList->slider;
}

return ret;
}

CircleListNode* CircleList_Next(CircleList* list) // O(1)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;

if( (sList != NULL) && (sList->slider != NULL) )
{
ret = sList->slider;
sList->slider = ret->next;
}

return ret;
}

main文件：

#include <stdio.h>
#include <stdlib.h>
#include "CircleList.h"

/* run this program using the console pauser or add your own getch, system("pause") or input loop */

struct Value
{
CircleListNode header;
int v;
};

/* run this program using the console pauser or add your own getch, system("pause") or input loop */

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, 5);
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);
}

printf("\n");

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* pv = (struct Value*)CircleList_Next(list);

printf("%d\n", pv->v);
}

printf("\n");

CircleList_Reset(list);

while( CircleList_Length(list) > 0 )
{
struct Value* pv = NULL;

for(i=1; i<3; i++)
{
CircleList_Next(list);
}

pv = (struct Value*)CircleList_Current(list);

printf("%d\n", pv->v);

CircleList_DeleteNode(list, (CircleListNode*)pv);
}

CircleList_Destroy(list);
return 0;
}

运行结果：



总结：

1.循环链表只是在单链表的基础上做了一个加强

2. 循环链表可以完全取代单链表的使用

3.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