线性表：循环链表

来自https://www.bilibili.com/video/av2975983/?p=17&t=13
个人感悟：循环链表的插入与删除与普通链表的区别就是在一个结点   而且初始化功能循环链表的头指向尾则代表空  普通链表头指针指针域指向NULL为空

//算法描述
//链表存储结构定义 
typedef struct CLinkList
{
    int data;
    struct ClinkList *next;
}node;
#define LEN sizeof(node)
//初始化循环链表
void ds_init(node **pNode)
{
    int item;
    node *temp;
    node *target;
    
    printf("输入结点的值，输入0完成初始化");
    
    while(1)
    {
        scanf("%d",&item);
        
        if(item == 0)
        return;
        
        if((*pNode) == NULL)
        {//循环链表只有一个结点 
            *pNode = (node *)malloc(LEN);
            if(!(*pNode))
            exit(1);
            (*pNode)->data = item;
            (*pNode)->next = *pNode;
        }
        else
        {   //target最终指向最后一个结点 
            for(target = (*pNode);target->next != (*pNode);target = target->next)
            
            temp = (node *)malloc(LEN);
            if(!temp)
            exit(1);
            
            temp->data = item;
            temp->next = *pNode;
            target->next = temp;
        }
    } 
} 

//插入结点
void ds_insert(node **pNode,int i)//参数：链表的第一个结点，插入的位置 
{
    node *temp;
    node *target;
    node *p;
    int item;
    int j = 1;
    
    printf("输入要插入结点的值：");
    scanf("%d",&item);
    
    if(i == 1)
    { //新插入的结点作为第一个结点 
        temp = (node *)malloc(LEN);
        
        if(!temp)
        exit(1);
        
        temp->data = item;
        //寻找最后一个结点
        for(target = (*pNode); target->next != (*pNode); target = target->next); 
        
        temp->next = (*pNode);
        target->next = temp;
        *pNode = temp;
    }
    else
    {
        target = *pNode; //target指向第一个元素 
        
        for(j; j < (i-1); j++)//找到要插入的位置  
        {
            target = target->next;
        }
        target = (node *)malloc(LEN);
        
        if(!temp)
        exit(0);
        
        temp->data = item; 
        p = target->next; //p作为中间变量 
        target->next = temp; //target指向新插入的结点 
        temp->next = p; //新插入的结点指向 p中存的是旧版本的第i个位置的结点 
    }
}
//删除结点
void ds_delete(node **pNode,int i)
{
    node *target;
    node temp;
    int j = 1;
    
    if(i == 1)
    {
        //删除的是第一个结点
        //找到最后一个结点
        for(target = *pNode; target->next != *pNode; target = target->next);
        
        temp = *pNode; //保存第一个结点以删除 
        *pNode = (*pNode)->next;//第一个结点指向下一个结点 
        target->next = *pNode;//尾结点指向第一个结点 
        free(temp);//释放 
    }
    else
    {
        target = *pNode;
        
        for(; j < i-1; j++)
        {
            target = target->next;//target只是指向要删除的结点  
        }
        
        temp = target->next;
        target->next = temp->next;
        free(temp);
    }
} 
//返回结点所在位置
int ds_search(node *pNode,int i)
{
    node *target;
    int i = 1;
    
    for(target = pNode; target->data != elem && target->next != pNode; i++)
    {
        target = target->nexxt;
    }
    
    if(target->next == pNode) //说明表中不存在该元素 
    return 0;
    else
    return i;
} 


相关代码实现：
#include <stdio.h>
#include <stdlib.h>

/*链表存储结构的定义*/
typedef struct CLinkList
{
    int data;
    struct CLinkList *next;
}node;

/************************************************************************/
/* 操作                                                                  */
/************************************************************************/

/*初始化循环链表*/
void ds_init(node **pNode)
{
    int item;
    node *temp;
    node *target;

    printf("输入结点的值，输入0完成初始化\n");

    while(1)
    {
        scanf("%d", &item);
        fflush(stdin);

        if(item == 0)
            return;

        if((*pNode) == NULL)
        { /*循环链表中只有一个结点*/
            *pNode = (node*)malloc(sizeof(struct CLinkList));
            if(!(*pNode))
                exit(0);
            (*pNode)->data = item;
            (*pNode)->next = *pNode;
        }
        else
        {
            /*找到next指向第一个结点的结点*/
            for(target = (*pNode); target->next != (*pNode); target = target->next)
                ;

            /*生成一个新的结点*/
            temp = (node *)malloc(sizeof(struct CLinkList));

            if(!temp)
                exit(0);

            temp->data = item;
            temp->next = *pNode;
            target->next = temp;
        }
    }
}

/*插入结点*/
/*参数：链表的第一个结点，插入的位置*/
void ds_insert(node **pNode , int i)
{
    node *temp;
    node *target;
    node *p;
    int item;
    int j = 1;

    printf("输入要插入结点的值:");
    scanf("%d", &item);

    if(i == 1)
    { //新插入的结点作为第一个结点
        temp = (node *)malloc(sizeof(struct CLinkList));

        if(!temp)
            exit(0);

        temp ->data = item;

        /*寻找到最后一个结点*/
        for(target = (*pNode); target->next != (*pNode); target = target->next)
            ;

        temp->next = (*pNode);
        target->next = temp;
        *pNode = temp;
    }
    else
    {
        target = *pNode;

        for( ; j < (i-1); ++j )
        {
            target=target->next;
        }

        temp = (node *)malloc(sizeof(struct CLinkList));

        if(!temp)
            exit(0);

        temp ->data = item;
        p = target->next;
        target->next = temp;
        temp->next = p;
    }
}

/*删除结点*/
void ds_delete(node **pNode, int i)
{
    node *target;
    node *temp;
    int j = 1;

    if(i == 1)
    { //删除的是第一个结点
        /*找到最后一个结点*/
        for(target = *pNode; target->next != *pNode;target = target->next)
            ;

        temp = *pNode;
        *pNode = (*pNode)->next;
        target->next = *pNode;
        free(temp);
    }
    else
    {
        target = *pNode;

        for( ; j < i-1; ++j )
        {
            target = target->next;
        }

        temp = target->next;
        target->next = temp->next;
        free(temp);
    }
}

/*返回结点所在位置*/
int ds_search(node *pNode, int elem)
{
    node *target;
    int i = 1;

    for(target = pNode; target->data != elem && target->next != pNode; ++i)
    {
        target = target->next;
    }

    if(target->next == pNode) /*表中不存在该元素*/
        return 0;
    else
        return i;
}

/*遍历*/
void ds_traverse(node *pNode)
{
    node *temp;
    temp = pNode;
    printf("***********链表中的元素******************\n");

    do
    {
        printf("%4d ", temp->data);
    }while((temp = temp->next) != pNode);

    printf("\n");
}

int main()
{
    node *pHead = NULL;
    char opp;
    int find;

    printf("1.初始化链表 \n\n2.插入结点 \n\n3.删除结点 \n\n4.返回结点位置 \n\n5.遍历链表  \n\n0.退出 \n\n请选择你的操作：");
    while(opp != '0')
    {
        scanf("%c", &opp);
        switch(opp)
        {
            case '1':
                ds_init(&pHead);
                printf("\n");
                ds_traverse(pHead);
                break;

            case '2':
                printf("输入需要插入结点的位置？");
                scanf("%d",  &find);
                ds_insert(&pHead, find);
                printf("在位置%d插入值后：\n",  find);
                ds_traverse(pHead);
                printf("\n");
                break;

            case '3':
                printf("输入需要删除的结点位置？");
                scanf("%d",  &find);
                ds_delete(&pHead, find);
                printf("删除第%d个结点后:\n",  find);
                ds_traverse(pHead);
                printf("\n");
                break;

            case '4':
                printf("你要查找倒数第几个结点的值？");
                scanf("%d",  &find);
                printf("元素%d所在位置：%d\n",  find,  ds_search(pHead, find));
                //ListTraverse(L);
                printf("\n");
                break;

            case '5':
                ds_traverse(pHead);
                printf("\n");
                break;

            case '0':
                exit(0);
        }
    }

    return 0;
}

//自己实践的代码
一个简单的创建以及输出
#include<stdio.h>
#include<stdlib.h>

typedef struct Node
{
    int data;
    struct Node *next;
}LinkList;

#define LEN sizeof(LinkList)

LinkList *initList()  //设置头结点 
{
    int dat;
    LinkList *temp;
    LinkList *target;
    LinkList *pNode = NULL;
    
    printf("输入以0结束\n");
    
    while(1)
    {
        scanf("%d",&dat);
        if(dat == 0)
        break;
        
        if(pNode == NULL)
        {
            pNode = (LinkList *)malloc(LEN);
            if(pNode == NULL)
            exit(1);
            pNode->data = dat;
            pNode->next = pNode;
        }
        else
        {
            for(target=pNode; target->next!=pNode; target=target->next);
            
            temp = (LinkList *)malloc(LEN);
            if(temp == NULL)
            exit(1);
            
            temp->data = dat;
            temp->next = pNode;  //新插入数据的指针域指向头 
            target->next = temp; //指向末尾结点的target指向新插入的结点 
        }
        
    } 
    
    return pNode;
    
}

void printList(LinkList *pNode)
{
    LinkList *temp;
    temp = pNode;
    printf("链表中的元素是：\n");
    
    do
    {
        printf("%4d",temp->data);
        temp = temp->next;
    }while(temp != pNode);
    printf("\n");
}

int main(void)
{
    LinkList *pNode;
    LinkList *L;
    pNode = initList();   
    printList(pNode);
    
    return 0;
}