链表从指定前方插入节点

在链表的前方插入节点

#include<stdio.h>

struct Test
{
  int data;
  struct Test * next;
};

printfLink(struct Test * head)
{
   while(head!=NULL)
   {
      printf("%d\n",head->data);
      head=head->next;
   }
   putchar('\n');
}

struct Test * InsertBeforeNode(struct Test *head,int data,struct Test * new)
{
    struct Test * p=head;
   if(p->data==data)
   {
     new->next=head;
     return new;
   }
    while(p->next!=NULL)
    {
       if(p->next->data==data)
       {
          new->next=p->next;
          p->next=new;
          printf("insert OK\n");
          return head;
       }
       p=p->next;
       printf("no insert\n");
    }
    return head;
}

void InsertAfterNode(struct Test *head,int data,struct Test *new)
{
    struct Test * p=head;
    while(p!=NULL)
    {
        if(p->data==data)
        {
           new->next=p->next;
           p->next=new;
        }
        p=p->next;
    }
}

int main()
{
   struct Test head={1,NULL};
   struct Test new1={2,NULL};
   struct Test new2={3,NULL};
   struct Test new3={4,NULL};
   InsertAfterNode(&head,1,&new1);
   printf("after insert:\n");
   printfLink(&head);
   struct Test *hp=InsertBeforeNode(&head,2,&new3);
   printf("after insert:\n");
   printfLink(hp)；
   return 0;
}

首先通过InsertAfterNode在data=1的节点的后面插入一个new1节点，然后通过InsertBeforeNode在data=2的节点前插入一个new3节点

输出结果：

after insert:
1
2
insert OK
after insert:
1
4
2