两个有序链表序列的合并

题目要求如下：

7-51 两个有序链表序列的合并（20 分）
已知两个非降序链表序列S1与S2，设计函数构造出S1与S2的并集新非降序链表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:
在一行中输出合并后新的非降序链表，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 3 5 -1
2 4 6 8 10 -1
输出样例:
1 2 3 4 5 6 8 10

C语言code：

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

struct lian { //定义链表结构 
    int data; //数据区 
    struct lian *next; //指向自身的结构指针 
};

struct lian *Randlian()  //创建链表 
{
    int x;
    struct lian *h, *s, *p;
    p = (struct lian *)malloc(sizeof(struct lian));
    s = (struct lian *)malloc(sizeof(struct lian));
    h = NULL;
    scanf("%d", &x);
    if(x != -1) {
        h = s;
    }
    while(x != -1) {
        p = s;
        s->data = x;
        s = (struct lian *)malloc(sizeof(struct lian));
        p->next = s;
        scanf("%d", &x);
    }
    p->next = NULL;

    return h;
}

struct lian *Addlian(struct lian *l1, struct lian *l2) //合并链表 
{
    struct lian *head, *h1, *h2, *p, *s1, *s2;
    h1 = s1 = l1;
    h2 = s2 = l2;
    head = NULL;
    if((s1 != NULL) && (s2 == NULL)) {
        head = h1;
    }
    else if((s1 == NULL) && (s2 != NULL)) {
        head = h2;
    }
    else if(s1 != NULL && s2 != NULL) {
        if(s1->data < s2->data) {
            head = h1;
            p = s1;
            s1 = p->next;
        }
        else {
            head = h2;
            p = s2;
            s2 = p->next;
        }   
        while(1) {
            if(s1->data < s2->data) {
                p->next = s1;
                p = s1;
                s1 = p->next;
                if(s1 == NULL) {
                    p->next = s2;
                    break;
                }
            }
            else{
                p->next = s2;
                p = s2;
                s2 = p->next;
                if(s2 == NULL) {
                    p->next = s1;
                    break;
                }
            }
        }
    }

    return head;
}

void Putlian(struct lian *l)  //打印新链表 
{
    struct lian *p;
    p = l;
    if(p != NULL){
        printf("%d", p->data);
        p = p->next;
        while(p) {
            printf(" %d", p->data);
            p = p->next;
        }
    }
    else {
        printf("NULL");
    }
}

int main(void)
{
    struct lian *h1, *h2;
    h1 = Randlian(); 
    h2 = Randlian();
    Putlian(Addlian(h1, h2));

    return 0;
}