用C语言写两个非降序链表的并集，例如将链表1->2->3 和 2->3->5 并为 1->2->3->5，只能输出结果，不能修改两个链表的数据。

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

typedef struct node {
    int val;
    struct node *next;
} Node;

Node *merge(Node *l1, Node *l2) {
    Node *dummy = (Node *)malloc(sizeof(Node));
    Node *cur = dummy;
    while (l1 && l2) {
        if (l1->val < l2->val) {
            cur->next = l1;
            l1 = l1->next;
        } else {
            cur->next = l2;
            l2 = l2->next;
        }
        cur = cur->next;
    }
    cur->next = l1 ? l1 : l2;
    return dummy->next;
}

int main() {
    Node *l1 = (Node *)malloc(sizeof(Node));
    l1->val = 1;
    l1->next = (Node *)malloc(sizeof(Node));
    l1->next->val = 2;
    l1->next->next = (Node *)malloc(sizeof(Node));
    l1->next->next->val = 3;
    l1->next->next->next = NULL;

    Node *l2 = (Node *)malloc(sizeof(Node));
    l2->val = 2;
    l2->next = (Node *)malloc(sizeof(Node));
    l2->next->val = 3;
    l2->next->next = (Node *)malloc(sizeof(Node));
    l2->next->next->val = 5;
    l2->next->next->next = NULL;

    Node *result = merge(l1, l2);

    while (result) {
        printf("%d ", result->val);
        result = result->next;
    }
    printf("\n");

    return 0;
}