7-51 两个有序链表序列的合并 (20分)

#include <iostream>
using namespace std;
typedef struct node
{
    int id;
    struct node* next;
}*L;
int main()
{
    L l1=NULL, l2=NULL, l3=NULL;//三个链表
    int cnt = 0;//结点总数
    int in;//输入的数据
  L p = NULL;//临时保存链表头
    while (1)
    {
    scanf("%d",&in);
        if (in == -1)break;
        cnt++;
        if (NULL == l1)
        {
            l1 = new struct node;
            l1->id = in;
            l1->next = NULL;
      p = l1;
        }
        else
        {
            struct node* s = new struct node;
            s->next = NULL;
            s->id = in;
            l1->next = s;
      l1=l1->next;
        }
    }
  l1=p;
    while (1)
    {
        cin >> in;
        if (in == -1)break;
        cnt++;
        if (NULL == l2)
        {
            l2 = new struct node;
            l2->id = in;
            l2->next = NULL;
      p=l2;
        }
        else
        {
            struct node* s = new struct node;
            s->next = NULL;
            s->id = in;
            l2->next = s;
      l2 = l2->next;
        }
    }    
  l2=p;
    p=NULL;
    for (int i = 0; i < cnt; i++)
    {
        struct node* s = new struct node;
        s->next = NULL;
        if (!l3)
        {
            l3= s;
            p = l3;
        }
        else
        {
            l3->next = s; 
      l3=l3->next;
        }
    }
    l3 = p;
    while (l1 || l2)
    {
        if (((l1 && l2) &&(l1->id < l2->id)) || (l1 && !l2))
        {
            l3->id = l1->id;    
            printf("%d", l3->id);
            l1 = l1->next;
            l3 = l3->next;
        }
        else if (((l1 && l2) && (l1->id >= l2->id)) || (!l1 && l2))
        {
            l3->id = l2->id;
            printf("%d", l3->id);
            l2 = l2->next;
            l3 = l3->next;
        }
        if (NULL != l2 || NULL != l1)
            printf(" ");
    }
    l3 = p;
    if (!l3)printf("NULL");
    return 0;
}