C语言版本：循环单链表的实现

SClist.h

#ifndef __SCLIST_H__
#define __SCLIST_H__

#include<cstdio>
#include<malloc.h>
#include<assert.h>
typedef int ElemType;
typedef struct Node {
    ElemType data;
    struct Node *next;
}Node,*PNode;

typedef struct List {
    PNode first;
    PNode last;
    size_t size;
}List;

void InitSClist(List *list);//初始化循环单链表
void push_back(List *list, ElemType x);//在循环单链表的末尾插入元素
void push_front(List *list, ElemType x);//在循环单链表的头部插入元素
void show_list(List *list);//打印循环单链表
void pop_back(List *list);//删除循环单链表的最后一个元素
void pop_front(List *list);//删除循环单链表的第一个元素
void insert_val(List *list, ElemType val);//将数据元素插入到循环单链表中（要求此时循环单链表中的数据元素顺序排列）
Node* find(List *list, ElemType x);//查找循环单链表中数据值为x的结点
int length(List *list);//求循环单链表的长度
void delete_val(List *list, ElemType x);//按值删除循环单链表中的某个数据元素
void sort(List *list);//对循环单链表进行排序
void reverse(List *list);//逆置循环单链表
void clear(List *list);//清除循环单链表
void destroy(List *list);//摧毁循环单链表

//优化
Node* _buynode(ElemType x);//创建结点

#endif

SClist.cpp

#include"SClist.h"

Node* _buynode(ElemType x) {
    Node *s = (Node*)malloc(sizeof(Node));
    assert(s != NULL);
    s->data = x;
    s->next = NULL;
    return s;
}

void InitSClist(List *list) {
    Node *s = (Node*)malloc(sizeof(Node));
    assert(s != NULL);
    list->first = list->last = s;
 15     list->last->next = list->first;//让链表最后一个结点的指针域指向头结点，从而时链表循环
    list->size = 0;
}

void push_back(List *list, ElemType x) {
    Node *s = _buynode(x);
    list->last->next = s;
    list->last = s;
 23     list->last->next = list->first;
    list->size++;
}

void push_front(List *list, ElemType x) {
    Node *s = _buynode(x);
    s->next = list->first->next;
    list->first->next = s;
 31     if (list->last == list->first)
 32         list->last = s;
    list->size++;
}

void show_list(List *list) {
    Node *p = list->first->next;
    while (p != list->first) {
        printf("%d->", p->data);
        p = p->next;
    }
    printf("Nul.
");
}

void pop_back(List *list) {
    if (list->size == 0) return;
    Node *p = list->first;
    while (p->next != list->last)
        p = p->next;
    free(list->last);
    list->last = p;
 52     list->last->next = list->first;
    list->size--;
}

void pop_front(List *list) {
    if (list->size == 0) return;
    Node *p = list->first->next;
    list->first->next = p->next;
 60     if (list->size == 1)
 61         list->last = list->first;
    free(p);
    list->size--;
}

void insert_val(List *list, ElemType x) {
    Node *p = list->first;
    while (p->next != list->last && p->next->data < x)
        p = p->next;
    if (p->next == list->last && p->next->data < x)
        push_back(list, x);
    else {
        Node *s = _buynode(x);
        s->next = p->next;
        p->next = s;
        list->size++;
    }
}

Node* find(List *list, ElemType key) {
    if (list->size == 0) return NULL;
    Node *p = list->first->next;
    while(p != list->first && p->data != key)
        p = p->next;
 85     if (p == list->first)
 86         return NULL;
    return p;
}


int length(List *list) {
    return list->size;
}

void delete_val(List *list, ElemType x) {
    if (list->size == 0) return;
    Node *p = find(list, x);
    if (p == NULL) {
        printf("没有要删除的数据!
");
        return;
    }
    if (p == list->last)
        pop_back(list);
    else {
        Node *q = p->next;
        p->data = q->data;
        p->next = q->next;
        free(q);
        list->size--;
    }
}

void sort(List *list) {
    if (list->size == 0 || list->size == 1) return;
    Node *s = list->first->next;
    Node *q = s->next;
    list->last->next = NULL;
    list->last = s;
    list->last->next = list->first;
    while (q != NULL) {
        s = q;
        q = q->next;
        Node *p = list->first;
        while (p->next != list->last && p->next->data < s->data)
            p = p->next;
        if (p->next == list->last &&p->next->data < s->data) {
            list->last->next = s;
            list->last = s;
            list->last->next = list->first;
        }
        else {
            s->next = p->next;
            p->next = s;
        }
    }
}

void reverse(List *list) {
    if (list->size == 0 || list->size == 1) return;
    Node *p = list->first->next;
    Node *q = p->next;
    list->last->next = NULL;
    list->last = p;
    list->last->next = list->first;
    while (q != NULL) {
        p = q;
        q = q->next;
        p->next = list->first->next;
        list->first->next = p;
    }
}

void clear(List *list) {
    Node *p = list->first->next;
    while (p != list->first) {
        list->first->next = p->next;
        free(p);
        p = list->first->next;
    }
    list->last = list->first;
    list->last->next = list->first;
    list->size = 0;
}

void destroy(List *list) {
    clear(list);
    free(list->first);
    list->first = list->last = NULL;
}

main.cpp

#include"SClist.h"

void main() {
    List mylist;
    InitSClist(&mylist);

    ElemType item;
    Node *p = NULL;
    int select = 1;
    while (select) {
        printf("*******************************************
");
        printf("*[1]  push_back        [2]  push_front    *
");
        printf("*[3]  show_list        [4]  pop_back      *
");
        printf("*[5]  pop_front        [6]  insert_val    *
");
        printf("*[7]  find             [8]  length        *
");
        printf("*[9]  delete_val       [10] sort          *
");
        printf("*[11] reverse          [12] clear         *
");
        printf("*[13*] destroy         [0]  quit_system   *
");
        printf("*******************************************
");
        printf("请选择：>>");
        scanf("%d", &select);
        if (select == 0) break;
        switch (select) {
        case 1:
            printf("请输入要插入的数据（-1结束）:>");
            while (scanf("%d", &item), item != -1) {
                push_back(&mylist, item);
            }
            break;
        case 2:
            printf("请输入要插入的数据（-1结束）:>");
            while (scanf("%d", &item), item != -1) {
                push_front(&mylist, item);
            }
            break;
        case 3:
            show_list(&mylist);
            break;
        case 4:
            pop_back(&mylist);
            break;
        case 5:
            pop_front(&mylist);
            break;
        case 6:
            printf("请输入要插入的数据:>");
            scanf("%d", &item);
            insert_val(&mylist, item);
            break;
        case 7:
            printf("请输入要查找的数据:>");
            scanf("%d", &item);
            p = find(&mylist, item);
            if (p == NULL)
                printf("要查找的数据在单链表中不存在！
");
            break;
        case 8:
            printf("单链表的长度为%d
", length(&mylist));
            break;
        case 9:
            printf("请输入要删除的值:>");
            scanf("%d", &item);
            delete_val(&mylist, item);
            break;
        case 10:
            sort(&mylist);
            break;
        case 11:
            reverse(&mylist);
            break;
        case 12:
            clear(&mylist);
            break;
            //case 13:
            //destroy(&mylist);
            //break;
        default:
            printf("选择错误,请重新选择！
");
            break;
        }
    }
    destroy(&mylist);
}