双指针

• 82. 删除排序链表中的重复元素 II
• [15. 三数之和](https://blog.csdn.net/qq_43788026/article/details/119736076)

82. 删除排序链表中的重复元素 II

//双指针
public ListNode deleteDuplicates(ListNode head) {
    if (head ==null || head.next == null){
        return head;
    }

    ListNode re = new ListNode();
    re.next = head;

    ListNode pre = re;
    ListNode cur = head;
    while (cur != null && cur.next !=null) {
        if (cur.val == cur.next.val) {
            while (cur.next != null && cur.val == cur.next.val) {
                cur = cur.next;
            }
            pre.next = cur.next;
            cur = cur.next;
        } else {
            pre = cur;
            cur = cur.next;
        }
    }
    return re.next;
}

//递归
public ListNode deleteDuplicates1(ListNode head) {
    if (head == null) return head;
    if (head.next != null && head.val == head.next.val) {
        while (head.next != null && head.val == head.next.val) {
            head = head.next;
        }
        return deleteDuplicates1(head.next);
    }else {
        head.next = deleteDuplicates1(head.next);
    }
    return head;
}

15. 三数之和