4、循环单链表

1、代码实现

#include<stdio.h>
#include<malloc.h>
#include<assert.h>
typedef int ElemType;

typedef struct Node{
    ElemType data;
    struct Node* next;
}Node,*PNode;

typedef struct SCList{
    PNode first;
    PNode last;
    int size;
}SCList;


void initSCList(SCList* list){
    //申请空间 创建虚拟头节点 
    Node* node = (Node*)malloc(sizeof(Node));
    assert(node != NULL);
    //第一个节点 和 最后一个节点 指向虚拟头节点 
    list->first = list->last = node;
    //虚拟头结点指向自己完成循环 
    node->next = node;
    //当前链表大小为0 
    list->size = 0;
}

//申请节点 
Node* malloc_node(ElemType e){
    Node* node = (Node* )malloc(sizeof(Node));
    assert(node != NULL);
    node->next = NULL;
    node->data = e;
    return node;
}

//尾插 
void push_back(SCList* list,ElemType e){
    //申请新节点 
    Node* node = malloc_node(e);
    //链表最后一个节点指向新节点 
    list->last->next = node;
    //更新last指针 
    list->last = node;
    //新节点的next指向第一个节点 形成循环 
    node->next = list->first;
    //元素数量+1 
    list->size++;
}

//头插 
void push_front(SCList* list,ElemType e){
    //申请新节点 
    Node* node = malloc_node(e);
    node->next = list->first->next;
    list->first->next = node;
    //判断当前链表是否为空 
    if(list->first == list->last){
        //为空当前插入的节点则为last所指向的节点 
        list->last = node;
    }
    list->size++;
}
//打印链表
void show_SCList(SCList* list){
    Node* p = list->first->next;
    while(p != list->first){
        printf("%d->",p->data);
        p = p->next;
    }
    printf("NULL .\n last=%d,size=%d",list->last->data,list->size);
} 

//删除尾部 
void pop_back(SCList* list){
    if(list->size == 0){
        //当前链表为空
        printf("当前链表为空,不可删除.\n");
        return; 
    }    
    PNode p = list->first;
    while(p->next != list->last){
        p = p->next;
    }
    free(list->last);
    list->last = p;
    p->next = list->first;
    list->size--;
}

//删除头部
void pop_front(SCList* list){
    if(list->size == 0){
        //当前链表为空
        printf("当前链表为空,不可删除.\n");
        return; 
    }
    
    Node* node = list->first->next;
    list->first->next = node->next;
    if(list->size == 1){
        //说明删除的是最后一个元素
        list->last = list->first; 
    }
    free(node);
    list->size--;
} 

//插入元素 [默认链表升序排序] 
void insert_val(SCList* list,ElemType e){
    Node* node = malloc_node(e);
    Node* p = list->first;
    while(p->next != list->first && p->next->data < e){
        p = p->next;
    } 
    node->next = p->next;
    p->next = node;
    if(node->next == list->first){
        //说明插入的位置是末尾
        list->last = node; 
    }
    list->size++;
}

//查找元素
Node* find(SCList* list,ElemType key){
    if(list->first == list->last){
        return NULL;
    } 
    Node* p = list->first->next;
    while(p != list->first){
        if(p->data == key){
            return p;
        }
        p = p->next;
    }
    return NULL;
} 

//返回链表长度
int length(SCList list){
    return list.size;
}

//按值删除
void delete_val(SCList* list,ElemType e){
    if(list->size == 0){
        return;
    }
    Node* p = find(list,e);
    if(p == NULL){
        return;
    }
    if(p->next == list->last){
        pop_back(list);
    }else{
        p->data = p->next->data;
        p->next = p->next->next; 
        free(p);
        list->size--;
    }
} 

//排序
void sort(SCList* list){
    if(list->size <= 1){
        return;
    }
    //指向第一个节点 
    Node* p = list->first->next;
    //指向第二个节点 
    Node* q = p->next;
    
    //将原链表最后一个节点指向NULL 
    list->last->next = NULL;
    //改变last指针指向第一个节点 
    list->last = p;
    //形成循环
    p->next = list->first; 
    
    while(q != NULL){
        p = q;
        q = q->next;
        Node* s = list->first; 
        //找到要插入的位置的上一个节点 
        while(s->next != list->first && s->next->data < p->data){
            s = s->next;
        } 
        //插入该节点
        p->next = s->next;
        s->next = p;
        if(s->next == list->first){
            //插入的位置是末尾
            list->last = p;
        }
    }
} 

//逆置链表
void reverse(SCList* list){
    if(list->size <= 1){
        return;
    }
    
    //指向第一个节点 
    Node* p = list->first->next;
    //指向第二个节点 
    Node* q = p->next;
    
    //将原链表最后一个节点指向NULL 
    list->last->next = NULL;
    //改变last指针指向第一个节点 
    list->last = p;
    //形成循环
    list->last->next = list->first;
     
    while(q != NULL){
        p = q;
        q = q->next;
    
        //头插法插入节点 
        p->next = list->first->next;
        list->first->next = p;
    } 
} 

//清空链表 
void clear(SCList* 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->next = list->first;
    list->size = 0;
} 

//销毁链表
void destroy(SCList* list){
    clear(list);
    free(list->first);
    list->first = list->last = NULL;
} 
int main(){
    SCList list;
    initSCList(&list);
    
    int select = 1;
    ElemType item = 0;
    while(select){
        printf("\n");
        printf("***********************************\n");
        printf("* [1] push_back   [2] push_front  *\n");        
        printf("* [3] show_list   [4] pop_back    *\n");
        printf("* [5] pop_front   [6] insert_val  *\n");
        printf("* [7] find        [8] length      *\n");
        printf("* [9] delete_val  [10] sort       *\n");
        printf("* [11] reverse    [12] clear      *\n");
        printf("* [13] destroy    [0] exit_system *\n");
        printf("***********************************\n");
        printf("请选择> ");
        scanf("%d",&select);
        if(!select){
            break;
        }
        PNode p = NULL;
        switch(select){
            case 1:
                printf("请输入要输入的数据(-1结束):>");
                while(scanf("%d",&item),item != -1){
                    push_back(&list,item);
                }
                break;
            case 2:
                printf("请输入要输入的数据(-1结束):>");
                while(scanf("%d",&item),item != -1){
                    push_front(&list,item);
                }
                break;
            case 3:
                show_SCList(&list);
                break;
            case 4:
                pop_back(&list);
                break;
            case 5:
                pop_front(&list);
                break;
            case 6:
                printf("请输入要插入的数据:>");
                scanf("%d",&item);
                insert_val(&list,item);
                break;
            case 7:
                printf("请输入要查找的数据:>");
                scanf("%d",&item);
                p = find(&list,item);
                if(p == NULL){
                    printf("查找的数据不存在.\n");
                }
                break;
            case 8:
                printf("该链表长度为: %d.\n",length(list));
                break;
            case 9:
                printf("请输入要删除的数据:>");
                scanf("%d",&item);
                delete_val(&list,item);
                break;    
            case 10:
                sort(&list);
                break;
            case 11:
                reverse(&list);
                break;
            case 12:
                clear(&list);
                break;
            case 13:
                destroy(&list);
                break; 
        }    
    }
    destroy(&list);
    return 0;
} 

2、排序和逆置代码画图演示