第十课，循环链表

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专题三：渐入佳境。包括以下章节：

无招胜有招-静态链表
气宗门道-循环链表
剑宗门道-双向链表
课后练习

单链表的局限

单链表可以用于表示任意的线性关系
有些线性关系是循环的，即没有队尾元素

单链表的改进

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

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循环链表的操作

循环链表拥有单链表的所有操作

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

这里写图片描述

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。

这里写图片描述

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

循环链表的应用

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。

这里写图片描述

小结

循环链表只是在单链表的基础上做了一个加强
循环链表可以完全取代单链表的使用
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

将单链表改写成循环链表

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() // 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;        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) // 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.c

#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;};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;}

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