第二题：

void removeDuplicates(ListNode *head) {
    // 在这里编写代码
    ListNode *p = head;
    while(p != NULL && p->next != NULL){
        ListNode *p1 = p->next;
        if(p->val != p1->val){
            p1 = p1->next;
            p = p->next;
            continue;
        }
        while(p1->next != NULL && p1->next->val == p->val)
            p1 = p1->next;
        p->next = p1;
        p = p->next;
        p1 = p1->next;
    }
}