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📜  数据结构-双链表

📅  最后修改于: 2020-10-15 00:45:38             🧑  作者: Mango

双链表

双链表是链表的一种复杂类型，其中节点包含指向序列中上一个节点和下一个节点的指针。因此，在双向链表中，节点由三部分组成：节点数据，指向顺序中下一个节点的指针(下一个指针)，指向上一个节点的指针(上一个指针)。图中显示了双向链接列表中的示例节点。

下图显示了一个双向链接列表，该列表包含三个节点，这些节点的数据部分中的数字从1到3。

在C语言中，双向链表中节点的结构可以表示为：

struct node 
{
    struct node *prev; 
    int data;
    struct node *next; 
}

第一个节点的上一个部分和最后一个节点的下一个部分将始终包含null，指示在每个方向上的结束。

在单链列表中，我们只能在一个方向上遍历，因为每个节点都包含下一个节点的地址，并且没有任何先前节点的记录。但是，双链表克服了单链表的这一局限性。由于列表中的每个节点都包含其先前节点的地址，因此，我们也可以使用存储在每个节点的先前部分中的先前地址来找到有关先前节点的所有详细信息。

双链表的内存表示

下图显示了双向链接列表的内存表示形式。通常，双向链表会为每个节点占用更多空间，因此会导致更广泛的基本操作，例如插入和删除。但是，由于列表在两个方向(向前和向后)都维护指针，因此我们可以轻松地操作列表的元素。

在下图中，列表的第一个元素(即13)存储在地址1。头指针指向起始地址1。由于这是添加到列表的第一个元素，因此列表的上一页包含null。列表的下一个节点位于地址4，因此第一个节点的下一个指针包含4。

我们可以用这种方式遍历列表，直到找到下一个包含null或-1的节点。

双链表上的操作

节点创建

struct node 
{
    struct node *prev;
    int data;
    struct node *next;
};
struct node *head;

下表描述了有关双链表的所有其余操作。

SN Operation Description
1 Insertion at beginning Adding the node into the linked list at beginning.
2 Insertion at end Adding the node into the linked list to the end.
3 Insertion after specified node Adding the node into the linked list after the specified node.
4 Deletion at beginning Removing the node from beginning of the list
5 Deletion at the end Removing the node from end of the list.
6 Deletion of the node having given data Removing the node which is present just after the node containing the given data.
7 Searching Comparing each node data with the item to be searched and return the location of the item in the list if the item found else return null.
8 Traversing Visiting each node of the list at least once in order to perform some specific operation like searching, sorting, display, etc.

C中的菜单驱动程序可实现双链表的所有操作

#include
#include
struct node
{
    struct node *prev;
    struct node *next;
    int data;
};
struct node *head;
void insertion_beginning();
void insertion_last();
void insertion_specified();
void deletion_beginning();
void deletion_last();
void deletion_specified();
void display();
void search();
void main ()
{
int choice =0;
    while(choice != 9)
    {
        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.Insert at any random location\n4.Delete from Beginning\n
        5.Delete from last\n6.Delete the node after the given data\n7.Search\n8.Show\n9.Exit\n");
        printf("\nEnter your choice?\n");
        scanf("\n%d",&choice);
        switch(choice)
        {
            case 1:
            insertion_beginning();
            break;
            case 2:
                    insertion_last();
            break;
            case 3:
            insertion_specified();
            break;
            case 4:
            deletion_beginning();
            break;
            case 5:
            deletion_last();
            break;
            case 6:
            deletion_specified();
            break;
            case 7:
            search();
            break;
            case 8:
            display();
            break;
            case 9:
            exit(0);
            break;
            default:
            printf("Please enter valid choice..");
        }
    }
}
void insertion_beginning()
{
   struct node *ptr; 
   int item;
   ptr = (struct node *)malloc(sizeof(struct node));
   if(ptr == NULL)
   {
       printf("\nOVERFLOW");
   }
   else
   {
    printf("\nEnter Item value");
    scanf("%d",&item);
    
   if(head==NULL)
   {
       ptr->next = NULL;
       ptr->prev=NULL;
       ptr->data=item;
       head=ptr;
   }
   else 
   {
       ptr->data=item;
       ptr->prev=NULL;
       ptr->next = head;
       head->prev=ptr;
       head=ptr;
   }
   printf("\nNode inserted\n");
}
   
}
void insertion_last()
{
   struct node *ptr,*temp;
   int item;
   ptr = (struct node *) malloc(sizeof(struct node));
   if(ptr == NULL)
   {
       printf("\nOVERFLOW");
   }
   else
   {
       printf("\nEnter value");
       scanf("%d",&item);
        ptr->data=item;
       if(head == NULL)
       {
           ptr->next = NULL;
           ptr->prev = NULL;
           head = ptr;
       }
       else
       {
          temp = head;
          while(temp->next!=NULL)
          {
              temp = temp->next;
          }
          temp->next = ptr;
          ptr ->prev=temp;
          ptr->next = NULL;
          }
           
       }
     printf("\nnode inserted\n");
    }
void insertion_specified()
{
   struct node *ptr,*temp;
   int item,loc,i;
   ptr = (struct node *)malloc(sizeof(struct node));
   if(ptr == NULL)
   {
       printf("\n OVERFLOW");
   }
   else
   {
       temp=head;
       printf("Enter the location");
       scanf("%d",&loc);
       for(i=0;inext;
           if(temp == NULL)
           {
               printf("\n There are less than %d elements", loc);
               return;
           }
       }
       printf("Enter value");
       scanf("%d",&item);
       ptr->data = item;
       ptr->next = temp->next;
       ptr -> prev = temp;
       temp->next = ptr;
       temp->next->prev=ptr;
       printf("\nnode inserted\n");
   }
}
void deletion_beginning()
{
    struct node *ptr;
    if(head == NULL)
    {
        printf("\n UNDERFLOW");
    }
    else if(head->next == NULL)
    {
        head = NULL; 
        free(head);
        printf("\nnode deleted\n");
    }
    else
    {
        ptr = head;
        head = head -> next;
        head -> prev = NULL;
        free(ptr);
        printf("\nnode deleted\n");
    }

}
void deletion_last()
{
    struct node *ptr;
    if(head == NULL)
    {
        printf("\n UNDERFLOW");
    }
    else if(head->next == NULL)
    {
        head = NULL; 
        free(head);    
        printf("\nnode deleted\n");
    }
    else 
    {
        ptr = head; 
        if(ptr->next != NULL)
        {
            ptr = ptr -> next; 
        }
        ptr -> prev -> next = NULL; 
        free(ptr);
        printf("\nnode deleted\n");
    }
}
void deletion_specified()
{
    struct node *ptr, *temp;
    int val;
    printf("\n Enter the data after which the node is to be deleted : ");
    scanf("%d", &val);
    ptr = head;
    while(ptr -> data != val)
    ptr = ptr -> next;
    if(ptr -> next == NULL)
    {
        printf("\nCan't delete\n");
    }
    else if(ptr -> next -> next == NULL)
    {
        ptr ->next = NULL;
    }
    else
    { 
        temp = ptr -> next;
        ptr -> next = temp -> next;
        temp -> next -> prev = ptr;
        free(temp);
        printf("\nnode deleted\n");
    }    
}
void display()
{
    struct node *ptr;
    printf("\n printing values...\n");
    ptr = head;
    while(ptr != NULL)
    {
        printf("%d\n",ptr->data);
        ptr=ptr->next;
    }
} 
void search()
{
    struct node *ptr;
    int item,i=0,flag;
    ptr = head; 
    if(ptr == NULL)
    {
        printf("\nEmpty List\n");
    }
    else
    { 
        printf("\nEnter item which you want to search?\n"); 
        scanf("%d",&item);
        while (ptr!=NULL)
        {
            if(ptr->data == item)
            {
                printf("\nitem found at location %d ",i+1);
                flag=0;
                break;
            } 
            else
            {
                flag=1;
            }
            i++;
            ptr = ptr -> next;
        }
        if(flag==1)
        {
            printf("\nItem not found\n");
        }
    }    
        
}

输出量

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
8

 printing values...

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
1

Enter Item value12

Node inserted

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
1

Enter Item value123

Node inserted

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
1

Enter Item value1234

Node inserted

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
8

 printing values...
1234
123
12

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
2

Enter value89

node inserted

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
3
Enter the location1
Enter value12345

node inserted

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
8

 printing values...
1234
123
12345
12
89

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.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.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
5

node deleted

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
8

 printing values...
123
12345

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
6

 Enter the data after which the node is to be deleted : 123

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
8

 printing values...
123

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
7

Enter item which you want to search?
123

item found at location 1 
*********Main Menu*********

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
6

 Enter the data after which the node is to be deleted : 123

Can't delete

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

Choose one option from the following list ...

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

1.Insert in begining
2.Insert at last
3.Insert at any random location
4.Delete from Beginning
5.Delete from last
6.Delete the node after the given data
7.Search
8.Show
9.Exit

Enter your choice?
9 

Exited..