83. 删除排序链表中的重复元素

class Solution {
    public ListNode deleteDuplicates(ListNode head) {
         ListNode dummy = new ListNode();
         dummy.next = head;
         ListNode pre = dummy, cur = head;
         while (cur != null) {
             // 注意别越界
             if (cur.next != null && cur.val == cur.next.val) { //重复了，跳一格
                 cur = cur.next;
                 pre.next = cur;
             } else { //不重复
                 cur = cur.next;
                 pre = pre.next;
             }
         }
         return dummy.next;
    }
}