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📜  数据结构-循环单链表

📅  最后修改于: 2020-10-15 00:46:31             🧑  作者: Mango

循环单链接列表

在循环单链接列表中，列表的最后一个节点包含一个指向列表的第一个节点的指针。我们可以有循环单链表以及循环双链表。

我们遍历循环的单链列表，直到到达开始的同一节点。循环单个喜欢的列表没有开头也没有结尾。在任何节点的下一部分中都没有空值。

下图显示了循环单链接列表。

循环链表主要用于操作系统中的任务维护。在计算机科学中有很多使用循环链接列表的示例，包括浏览器浏览，其中用户过去访问过的页面的记录以循环链接列表的形式维护，可以通过单击上一个按钮再次访问。

循环链表的内存表示形式：

在下图中，一个圆形链接列表的内存表示形式，其中包含4个科目的学生的成绩。但是，该图像显示了循环列表如何在内存中存储的情况。列表的开头或开头指向索引为1的元素，数据部分包含13个标记，下一部分包含4个标记。这意味着它与存储在列表第4个索引处的节点链接。

但是，由于我们正在考虑在内存中使用循环链接列表，因此列表的最后一个节点包含列表的第一个节点的地址。

我们还可以在内存中拥有多个链接列表，并且不同的起始指针指向列表中的不同起始节点。最后一个节点由其下一部分标识，该下一部分包含列表的起始节点的地址。我们必须能够确定任何链接列表的最后一个节点，以便我们能够找出遍历列表时需要执行的迭代次数。

循环单链表上的操作：

插入

SN Operation Description
1 Insertion at beginning Adding a node into circular singly linked list at the beginning.
2 Insertion at the end Adding a node into circular singly linked list at the end.

删除和遍历

SN Operation Description
1 Deletion at beginning Removing the node from circular singly linked list at the beginning.
2 Deletion at the end Removing the node from circular singly linked list at the end.
3 Searching Compare each element of the node with the given item and return the location at which the item is present in the list otherwise return null.
4 Traversing Visiting each element of the list at least once in order to perform some specific operation.

C语言中的菜单驱动程序，可实现所有操作

在循环单链表上

#include
#include
struct node 
{
    int data;
    struct node *next; 
};
struct node *head;

void beginsert (); 
void lastinsert ();
void randominsert();
void begin_delete();
void last_delete();
void random_delete();
void display();
void search();
void main ()
{
    int choice =0;
    while(choice != 7) 
    {
        printf("\n*********Main Menu*********\n");
        printf("\nChoose one option from the following list ...\n");
        printf("\n===============================================\n");
        printf("\n1.Insert in begining\n2.Insert at last\n3.Delete from Beginning\n4.Delete from last\n5.Search for an element\n6.Show\n7.Exit\n");
        printf("\nEnter your choice?\n");        
        scanf("\n%d",&choice);
        switch(choice)
        {
            case 1:
            beginsert();    
            break;
            case 2:
            lastinsert();        
            break;
            case 3:
            begin_delete();        
            break;
            case 4:
            last_delete();        
            break;
            case 5:
            search();        
            break;
            case 6:
            display();        
            break;
            case 7:
            exit(0);
            break;
            default:
            printf("Please enter valid choice..");
        }
    }
}
void beginsert()
{
    struct node *ptr,*temp; 
    int item; 
    ptr = (struct node *)malloc(sizeof(struct node));
    if(ptr == NULL)
    {
        printf("\nOVERFLOW");
    }
    else 
    {
        printf("\nEnter the node data?");
        scanf("%d",&item);
        ptr -> data = item;
        if(head == NULL)
        {
            head = ptr;
            ptr -> next = head;
        }
        else 
        {    
            temp = head;
            while(temp->next != head)
                temp = temp->next;
            ptr->next = head; 
            temp -> next = ptr; 
            head = ptr;
        } 
        printf("\nnode inserted\n");
    }
            
}
void lastinsert()
{
    struct node *ptr,*temp; 
    int item;
    ptr = (struct node *)malloc(sizeof(struct node));
    if(ptr == NULL)
    {
        printf("\nOVERFLOW\n");
    }
    else
    {
        printf("\nEnter Data?");
        scanf("%d",&item);
        ptr->data = item;
        if(head == NULL)
        {
            head = ptr;
            ptr -> next = head;    
        }
        else
        {
            temp = head;
            while(temp -> next != head)
            {
                temp = temp -> next;
            }
            temp -> next = ptr; 
            ptr -> next = head;
        }
        
        printf("\nnode inserted\n");
    }

}

void begin_delete()
{
    struct node *ptr; 
    if(head == NULL)
    {
        printf("\nUNDERFLOW");    
    }
    else if(head->next == head)
    {
        head = NULL;
        free(head);
        printf("\nnode deleted\n");
    }
    
    else
    {    ptr = head; 
        while(ptr -> next != head)
            ptr = ptr -> next; 
        ptr->next = head->next;
        free(head);
        head = ptr->next;
        printf("\nnode deleted\n");

    }
}
void last_delete()
{
    struct node *ptr, *preptr;
    if(head==NULL)
    {
        printf("\nUNDERFLOW");
    }
    else if (head ->next == head)
    {
        head = NULL;
        free(head);
        printf("\nnode deleted\n");

    }
    else 
    {
        ptr = head;
        while(ptr ->next != head)
        {
            preptr=ptr;
            ptr = ptr->next;
        }
        preptr->next = ptr -> next;
        free(ptr);
        printf("\nnode deleted\n");

    }
}

void search()
{
    struct node *ptr;
    int item,i=0,flag=1;
    ptr = head; 
    if(ptr == NULL)
    {
        printf("\nEmpty List\n");
    }
    else
    { 
        printf("\nEnter item which you want to search?\n"); 
        scanf("%d",&item);
        if(head ->data == item)
        {
        printf("item found at location %d",i+1);
        flag=0;
        }
        else 
        {
        while (ptr->next != head)
        {
            if(ptr->data == item)
            {
                printf("item found at location %d ",i+1);
                flag=0;
                break;
            } 
            else
            {
                flag=1;
            }
            i++;
            ptr = ptr -> next;
        }
        }
        if(flag != 0)
        {
            printf("Item not found\n");
        }
    }    
        
}

void display()
{
    struct node *ptr;
    ptr=head;
    if(head == NULL)
    {
        printf("\nnothing to print");
    }    
    else
    {
        printf("\n printing values ... \n");
        
        while(ptr -> next != head)
        {
        
            printf("%d\n", ptr -> data);
            ptr = ptr -> next;
        }
        printf("%d\n", ptr -> data);
    }
            
}

输出：

*********Main Menu*********

Choose one option from the following list ...

===============================================

1.Insert in begining
2.Insert at last
3.Delete from Beginning
4.Delete from last
5.Search for an element
6.Show
7.Exit

Enter your choice?
1

Enter the node data?10

node inserted

*********Main Menu*********

Choose one option from the following list ...

===============================================

1.Insert in begining
2.Insert at last
3.Delete from Beginning
4.Delete from last
5.Search for an element
6.Show
7.Exit

Enter your choice?
2

Enter Data?20

node inserted

*********Main Menu*********

Choose one option from the following list ...

===============================================

1.Insert in begining
2.Insert at last
3.Delete from Beginning
4.Delete from last
5.Search for an element
6.Show
7.Exit

Enter your choice?
2

Enter Data?30

node inserted

*********Main Menu*********

Choose one option from the following list ...

===============================================

1.Insert in begining
2.Insert at last
3.Delete from Beginning
4.Delete from last
5.Search for an element
6.Show
7.Exit

Enter your choice?
3

node deleted

*********Main Menu*********

Choose one option from the following list ...

===============================================

1.Insert in begining
2.Insert at last
3.Delete from Beginning
4.Delete from last
5.Search for an element
6.Show
7.Exit

Enter your choice?
4

node deleted

*********Main Menu*********

Choose one option from the following list ...

===============================================

1.Insert in begining
2.Insert at last
3.Delete from Beginning
4.Delete from last
5.Search for an element
6.Show
7.Exit

Enter your choice?
5

Enter item which you want to search?
20
item found at location 1
*********Main Menu*********

Choose one option from the following list ...

===============================================

1.Insert in begining
2.Insert at last
3.Delete from Beginning
4.Delete from last
5.Search for an element
6.Show
7.Exit

Enter your choice?
6

 printing values ... 
20

*********Main Menu*********

Choose one option from the following list ...

===============================================

1.Insert in begining
2.Insert at last
3.Delete from Beginning
4.Delete from last
5.Search for an element
6.Show
7.Exit

Enter your choice?
7