7-52 两个有序链表序列的交集 C语言

已知两个非降序链表序列S1与S2，设计函数构造出S1与S2的交集新链表S3。

输入格式:

输入分两行，分别在每行给出由若干个正整数构成的非降序序列，用−1表示序列的结尾（−1不属于这个序列）。数字用空格间隔。

输出格式:

在一行中输出两个输入序列的交集序列，数字间用空格分开，结尾不能有多余空格；若新链表为空，输出NULL。

输入样例:

1 2 5 -1
2 4 5 8 10 -1

输出样例:

2 5

  水平有限只会用很简陋的方法写,大数据还不知道能怎么优化????

代码示例:

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

typedef struct list* List;
struct list{
	int data;
	List next;
};

int main()
{
	int i,n,flag = 0;
	List s1,s2,s3,t,S1,S2,S3;
	S1 = (List)malloc(sizeof(struct list));
	S2 = (List)malloc(sizeof(struct list)); 
	S3 = (List)malloc(sizeof(struct list));
	S3->next = NULL;
	s1 = S1; 
	s2 = S2;
	s3 = S3;
	/* 往s1里输入数据 */
	while(1){
		scanf("%d",&n);
		if(n == -1) break;
		t = (List)malloc(sizeof(struct list));
		t->data = n;
		t->next = NULL;
		s1->next = t;
		s1 = s1->next;
	} 
	
	/* 往s2里输入数据 */
	while(1){
		scanf("%d",&n);
		if(n == -1) break;
		t = (List)malloc(sizeof(struct list));
		t->data = n;
		t->next = NULL;
		s2->next = t;
		s2 = s2->next;
	} 
	s1 = S1; 
	s2 = S2; 
 
	/* 判断交集并输入进s3 */
	while(s1->next != NULL && s2->next != NULL){
		if(s1->next->data == s2->next->data){
			s3->next = s1->next;
			s1 = s1->next;
			s2 = s2->next;
			s3 = s3->next;
		}else if(s1->next->data > s2->next->data){
			s2 = s2->next;
		}else{
			s1 = s1->next;
		}
	}
	
	/* 输出 */ 
	s3 = S3;
	if(s3->next == NULL){
		printf("NULL");
		return 0;
	}
	while(s3->next != NULL){
		if(!flag){
			flag = 1;
			printf("%d",s3->next->data);
		}else{
			printf(" %d",s3->next->data);
		}
		s3 = s3->next;
	}
}