删除双向链表中的第一个节点是最简单的操作。只需要将头指针复制到指针ptr并将头指针移动到下一个指针。
ptr = head;
head = head -> next;
现在使这个新头节点的prev指针指向NULL。这将通过使用以下语句来完成。
head -> prev = NULL;
现在使用free函数释放指针ptr。
free(ptr);
算法
第1步：如果HEAD = NULL
提示 内存溢出。
转到第6步
第2步：设置PTR = HEAD
第3步：设置HEAD = HEAD->NEXT
第4步：设置HEAD->PREV = NULL
第5步：释放PTR
第6步：退出
示意图
C语言实现示例代码 -
#include<stdio.h>
#include<stdlib.h>
void create(int);
void beginning_delete();
struct node
{
int data;
struct node *next;
struct node *prev;
};
struct node *head;
void main()
{
int choice, item;
do
{
printf("1.Append List\n");
printf("2.Delete node from beginning\n");
printf("3.Exit\n");
printf("4.Enter your choice ? ");
scanf("%d", &choice);
switch (choice)
{
case 1:
printf("Enter the item\n");
scanf("%d", &item);
create(item);
break;
case 2:
beginning_delete();
break;
case 3:
exit(0);
break;
default:
printf("Please enter valid choice\n");
}
} while (choice != 3);
}
void create(int item)
{
struct node *ptr = (struct node *)malloc(sizeof(struct node));
if (ptr == NULL)
{
printf("OVERFLOW\n");
}
else
{
if (head == NULL)
{
ptr->next = NULL;
ptr->prev = NULL;
ptr->data = item;
head = ptr;
}
else
{
ptr->data = item;printf("Press 0 to insert more ?\n");
ptr->prev = NULL;
ptr->next = head;
head->prev = ptr;
head = ptr;
}
printf("Node Inserted\n");
}
}
void beginning_delete()
{
struct node *ptr;
if (head == NULL)
{
printf("UNDERFLOW\n");
}
else if (head->next == NULL)
{
head = NULL;
free(head);
printf("Node Deleted\n");
}
else
{
ptr = head;
head = head->next;
head->prev = NULL;
free(ptr);
printf("Node Deleted\n");
}
}
执行上面示例代码，得到以下结果 -
1.Append List
2.Delete node from beginning
3.Exit
4.Enter your choice?1
Enter the item
12
Node Inserted
1.Append List
2.Delete node from beginning
3.Exit
4.Enter your choice?2
Node Deleted
1.Append List
2.Delete node from beginning
3.Exit
4.Enter your choice?
