83. 删除排序链表中的重复元素

输入: 1->1->2
输出: 1->2

输入: 1->1->2->3->3
输出: 1->2->3

 public ListNode deleteDuplicates(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode now = head;
        while (now.next != null) {
            if (now.val == now.next.val) {
                now.next = now.next.next;
            } else {
                now = now.next;
            }
        }
        return head;
    }