struct ListNode* mergeInBetween(struct ListNode* list1, int a, int b, struct ListNode* list2){
    struct ListNode* cur1 = list1;
    struct ListNode* pre = NULL;
    struct ListNode* end = list2;
    while(end->next != NULL)
    {
        end = end->next;  
    }
    while(a--)
    {
        pre = cur1;
        cur1 = cur1->next;
    }
    cur1 = list1;
    while(b--)
    {
        cur1 = cur1->next;
    }
    pre->next = list2;
    end->next = cur1->next;
    return list1;
}