单循环链表（C语言实现）

//clist.h
//结构体定义以及函数声明

#ifndef clist_h
#define clist_h

#include 
#include 
#include 
#include 

typedef  int elemtype;

typedef struct node
{
    elemtype data;
    struct node *next;
}node, *pnode;

typedef struct list
{
    pnode head;
    pnode tail;
    int size;
}list,*plist;

bool initlist(plist list);
void create_t(plist list,elemtype x);             //尾插
void create_h(plist list,elemtype x);             //头插
void del_back(plist list);                        //尾删
void del_front(plist list);                       //头删
void sortlist(plist list);                        //排序
void insert_val(plist list,elemtype x);           //按值插
pnode find(plist list,elemtype x);
void del_val(plist list,elemtype x);
void modify(plist list,elemtype x1,elemtype x2);
void clear(plist list);
void destroy(plist list);
void reserve(plist list);
int length(plist list);
void menu();
void showlist(plist list);
void show_tail(plist list);
elemtype next(plist list,elemtype x);
elemtype prio(plist list,elemtype x);
pnode prev(plist list,pnode p);

#endif

//clist.cpp
//函数实现

#include"clist.h"

void menu()           //提供选项的菜单函数
{
    printf("***************************************************************\n");
    printf("* [0] quit_system [1] create_t   [2] create_h    [3] showlist *\n");
    printf("* [4] del_back    [5] del_front  [6] insert_val  [7] show_tail*\n");
    printf("* [8] find        [9] del_val    [10] sortlist   [11] modify  *\n");
    printf("* [12]clear       [13]destroy    [14] resver     [15]length   *\n");
    printf("* [16] next       [17]prio                                    *\n");
    printf("***************************************************************\n");
}
bool initlist(plist list)
{
    list->head = (pnode)malloc(sizeof(node)); /初始化一个头结点
    assert(list->head != null);               //断言，表达式为真，接着往下执行

    list->head->next = list->head;            //初始化head和tail指针，使其都指向头节点
    list->tail = list->head;

    list->size = 0;                           //长度初始化为0
    return true;
}

void create_t(plist list,elemtype x)     //尾插法
{
    pnode s = (pnode)malloc(sizeof(node));
    assert(s != null);
    s->data = x;                         //填充数据域
    list->tail->next = s;                //tail指向最后一个节点，把新建立的节点链接到链表的最后
    s->next = list->head;                //单循环链表，新节点的next指向头结点           
    list->tail = s;                      //改变尾指针的指向
    list->size++;
} 
void showlist(plist list)            //链表显示函数
{
    if(1>list->size)
    {
        printf("--链表为空\n");
        return ;
    }
    pnode p = list->head->next;
    while(list->head != p)           //逐个遍历链表
    {
        printf("%d ",p->data);
        p=p->next;
    }
    printf("\n");
}
void create_h(plist list,elemtype x)  //头插法
{
    pnode s = (pnode)malloc(sizeof(node));
    assert(s != null);
    s->data = x;                             //填充数据域
    s->next = list->head->next;              //新节点指向第一个节点           
    list->head->next = s;                    //头节点的next指向新节点s
    if(list->size == 0)                      //如果是第一次头插，需改变尾指针和尾节点的next指向，之后都不改变
    {
        list->tail = s;
        list->tail->next = list->head;        
    }
    list->size++;        //插入一个，长度加1
}

void del_back(plist list)    //尾删
{
    if(0==list->size)
        return;
    pnode p = list->head;
    while(list->head != p->next->next)      //找到倒数第二个节点
    {
        p = p->next;
    }                      
    p->next = list->head;                   //把最后一个节点分离
    free(list->tail);                       //释放最后一个节点
    list->tail = p;                         //尾指针指向原来的倒数第二个节点（现在倒数第一）
    printf("--尾节点已删除\n");
    list->size--;
}

void del_front(plist list)   //头删
{
    if(0==list->size)
        return;
    else
    {
        pnode p = list->head->next;
        if(1==list->size) 
        {                                    //只有一个节点，若删去，需改变尾指针
            list->tail = list->head;
            list->head->next = list->head;
        }
        else
        {                
            list->head->next = p->next;      //头指针指向第二个节点    
        }
        free(p);                             //释放第一个节点
    }                            
    printf("--头节点已删除\n");
    list->size--;
}


void show_tail(plist list)     //为测试尾指针是否正确改变，需显示最后一个节点
{
    printf("--链表的尾节点是：》%d \n",list->tail->data);
}

void sortlist(plist list)      // 对无序链表进行从小到大排序
{
    if(2>list->size)
        return ;
    pnode p = list->head->next;
    pnode q = p->next;
    for(int i = 0;isize-1;i++,p = list->head->next,q = p->next)      //n个数比较n-1趟
    {
        for(int j = 0;jsize-1-i;j++,p=q,q=q->next)   //第i趟比较n-i次
        {
            if(p->data > q->data)        //如果前面的数大于后面，则交换
            {
                p->data = p->data + q->data;
                q->data = p->data - q->data;
                p->data = p->data - q->data;
            }
        }
    }
}

void insert_val(plist list,elemtype x)   //链表有序的前提下，给一个值插入
{
    pnode p = list->head->next,q = list->head;
    while(list->head != p)               //找到能插入的位置，会在p、q之间
    {   
        if(xdata)
            break;
        q = p;
        p = p->next;
    }
    pnode s = (pnode)malloc(sizeof(node)); //初始化新节点
    s->data = x;
    q->next = s;              //把新节点插入到链表中（在p,q之间插入）
    s->next = p;
    if(list->head == p)       //如果新节点的值最大，即尾插，需改变尾指针和尾节点的next指向
    {
        list->tail = s;
        list->tail->next=list->head;
    }
    list->size++;
}

pnode find(plist list,elemtype x)       //返回要查找元素的前面一个的地址
{
    pnode p = list->head;
    while(list->tail != p && list->head != p->next && x != p->next->data)
    {
        p = p->next;                   //循环结束，p指向x的前面一个元素
    }                      
    if(list->head == p->next)          //如果p指向最后一个元素，说明没有找到
    {
        printf("--没找到！\n");
        return null;
    }
    return p;
}

void del_val(plist list,elemtype x)     //删除指定的值x
{
    if(0 == list->size)
        return ;
    pnode p = find(list,x);
    pnode q = null;
    if(null != p)
    {
        q = p->next;               //q指向要删除的节点  
        if(q == list->tail)        //若删除最后一个节点，需改变尾指针
        {
            p->next = list->head;
            list->tail = p;
        }
        else
        {
            p->next = q->next;
        }
        free(q);                  //释放要删除的节点
        list->size--;
        printf("--%d已删除!\n",x);
    }
    return ;
}

void modify(plist list,elemtype x1,elemtype x2)    //把原有的x1修改成x2
{
    pnode p = find(list,x1);
    if(null != p)
        p->next->data = x2;
    else
        return ;
}

void clear(plist list)       //删除链表的所有节点，但不删除头结点
{
    pnode p = list->head->next;
    pnode q = p;
    while(list->head != p)      
    {
        p = p->next;         //p依次后移，跟屁虫q依次释放节点
        free(q);
        q = p;
    }
    list->tail = list->head;   //修改尾指针和链表长度
    list->head->next = list->head;
    list->size = 0;
    printf("--链表已被清空！\n");
}

void destroy(plist list)   //摧毁链表，包括所有节点和头结点
{
    clear(list);
    free(list->head);
    list->head = null;
    list->tail = null;
    printf("--链表已被摧毁！\n");
}

pnode prev(plist list,pnode p)     //返回p指向的前面一个节点
{
    if(p != list->head)
    {
        pnode q = list->head->next;
        while(q != list->head && q->next != p)  //依次往后移，知道尾指针的前面一个节点
            q=q->next;
        if(q->next == p)
            return q;
    }
    return null;
}
void reserve(plist list)   //逆置链表 
{
    pnode s = (pnode)malloc(sizeof(node));       //建立一个节点
    s->next = list->tail;
    pnode p = list->tail;
    while(list->tail != list->head->next)        //把原链表的尾节点到第一个节点依次连接到新节点上
    {
        list->tail = prev(list,list->tail);
        list->tail->next = list->head;
        p->next = list->tail;
        p=p->next;
    }
    p->next = s;              //p指向第一个节点，即新链表的最后一个节点，尾指针的next指向头结点s，链表结束
    free(list->head);         //释放原来的头结点
    list->head = s;           //把s变成新的头指针
}

int length(plist list)     //求链表的长度
{
    return list->size;
}

elemtype next(plist list,elemtype x)      //返回x的后继
{
    pnode p = find(list,x);  
    if(null == p) 
        return -1;
    if(p->next == list->tail)           //因为是单循环链表，尾节点的下一个元素是第一个节点
    {
        return list->head->next->data;    
    }
    p=p->next;
    return p->next->data;
}
elemtype prio(plist list,elemtype x)         //返回x的前驱
{
    pnode p = find(list,x);
    if(null != p)
    {
        if(p == list->head || p == list->tail)
        {
            return list->tail->data;
        }
        return p->data;
    }
    return -1;
}

//main.cpp
//测试函数

#include "clist.h"

int main()
{
    list mylist;
    initlist(&mylist);
    elemtype item = 0;
    int pos = 0;
    int chose = 1;
    pnode p = null;
    while(chose)
    {
        menu();
        printf("给出想要操作的序号：\n");
        scanf("%d",&chose);
        switch(chose)
        {
        case 0:
            destroy(&mylist);
            chose = 0;
            break;
        case 1:
            printf("输入要尾插的数据[-1结束]：\n");
            while(scanf("%d",&item),item!=-1)
            {
                create_t(&mylist,item);
            }
            break;
        case 2:
            printf("输入要头插的数据：\n");
            while(scanf("%d",&item),item!=-1)
            {
                create_h(&mylist,item);
            }
            break;
        case 3:
            showlist(&mylist);
            break;
        case 4:
            del_back(&mylist);
            break;
        case 5:
            del_front(&mylist);
            break;
        case 6:
            printf("给出要插入的数：\n");
            scanf("%d",&item);
            insert_val(&mylist,item);
            break;
        case 7:
            show_tail(&mylist);
            break;
        case 8:
            printf("输入要查找的数：\n");
            scanf("%d",&item);
            p = find(&mylist,item);
            if(null!=p)
                printf("%d\n",p->next->data);
            break;
        case 9:
            printf("输入要删除的数：\n");
            scanf("%d",&item);
            del_val(&mylist,item);
            break;
        case 10:
            sortlist(&mylist);
            break;
        case 11:
            printf("输入要修改的数和修改后的数\n");
            scanf("%d %d",&item,&pos);
            modify(&mylist,item,pos);
            break;
        case 12:
            clear(&mylist);
            break;            
        case 13:
            destroy(&mylist);
            break;
        case 14:
            reserve(&mylist);
            break;
        case 15:
            printf("链表长度为：%d\n",length(&mylist));
            break;
        case 16:
            printf("输入想要找哪个一数的后继：\n");
            scanf("%d",&item);
            printf("%d 的后继是：%d\n",item,next(&mylist,item));
            break;
        case 17:
            printf("输入想要找哪个一数的前驱：\n");
            scanf("%d",&item);
            printf("%d 的前驱是：%d\n",item,prio(&mylist,item));
            break;
        default:
            printf("重新输入\n");
            break;
        }   
    }
    return 0;
}