合并有序链表遇到的问题

Question

合并两个有序链表，学号如果相同就保留分高的一个，调试通过不了，而且感觉我写的有没有头结点这个地方就很混乱，麻烦指出错误修改程序，讲解详细一点
样例输入：
5
20303 62
20304 75
20307 87
20311 89
20320 79
6
20301 99
20302 65
20307 92
20311 87
20322 83
20323 88
样例输出
20301 99
20302 65
20303 62
20304 75
20307 92
20311 89
20320 79
20322 83
20323 88

#include<stdio.h>
#include<string.h>
#include <stdlib.h>


struct  data_array{
   long num;
   int score;
 };
typedef  struct student{
  long num;
  int score;
  struct student *next;
} NODE;
NODE * create(int n)
{
    int i;
    NODE *head,*p,*tail;
    head=(NODE*)malloc(sizeof(NODE));//创建头结点
    tail=head;
    p=head;
    head->num=0;
    head->score=0;
    for(i=0;i<n;i++)
    {
        p=(NODE*)malloc(sizeof(NODE));//申请下一个节点
        scanf("%ld %d",&p->num,&p->score);
        tail->next=p;
        tail=p;
    }
    tail->next=NULL;
    return head;
}
void display (NODE *head)
{
    NODE *p;
    p=head->next;//原先是p=head就不行
    while(p!=NULL)
    {
        printf("%ld %d\n",p->num,p->score);
        p=p->next;
    }
    printf("----\n");
}
NODE* merge(NODE *head1, NODE *head2)
{
    NODE *head=NULL;
    NODE *l1=NULL,*l2=NULL;
    head = (NODE*)malloc(sizeof(NODE));
    l1=head1->next;
    l2=head2->next;
    
    if(l1->num<l2->num)
    {
        head=l1;
        l1=l1->next;
    }
    else
    {
        head=l2;
        l2=l2->next;
    }
    NODE *tail=head;
    while(l1!=NULL&&l2!=NULL)//?
    {
        if(l1->num<l2->num)
        {
            tail->next=l1;
            l1=l1->next;
        }
        else if(l1->num>l2->num)
        {
            tail->next=l2;
            l2=l2->next;
        }
        else
        {
            if(l1->score>=l2->score)
            {
                tail->next=l1;
            }
            else
            {
                tail->next=l2;
            }
            l1=l1->next;
            l2=l2->next;
        }
        tail=tail->next;
    }
    if (l1!=NULL)
        tail->next = l1;    
    if (l2!=NULL)
        tail->next = l2;
    NODE *first=head->next;
    free(head);
    return first;
}
//void del(NODE *head1, NODE *head2)



    

int main(void)
{
    NODE *head1,*head2;
    NODE *head;
    int num1,num2;
    scanf("%d",&num1);
    getchar();
    head1=create(num1);
    scanf("%d",&num2);
    getchar();
    head2=create(num2);
    display(head1);
    display(head2);
    head=merge(head1,head2);
    display(head);
}

Answer 1

要不就重写一个，要不就在你的代码上修改，怎么说