removeDuplicates(链表)

https://leetcode.com/problems/remove-duplicates-from-sorted-list/
Input: 1->1->2
Output: 1->2

    public ListNode deleteDuplicates(ListNode head) {
   ListNode res = head;
        while (head != null && head.next != null) {
            if (head.val == head.next.val) {
                head.next = head.next.next;
                continue;
            }
            head = head.next;
        }
        return res;
    }

https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/
Input: 1->2->3->3->4->4->5
Output: 1->2->5

          if (head == null || head.next == null) {
            return head;
        }
        ListNode res = new ListNode(-1);
        ListNode pre = res;
        res.next = head;
        while (pre.next != null) {
            ListNode cur = pre.next;
            while (cur.next != null && cur.next.val == cur.val) {
                cur = cur.next;
            }
            if (cur != pre.next) {
                pre.next = cur.next;
            } else {
                pre = pre.next;
            }
        }
        return res.next;