删除链表中重复的元素

有序链表：
输入: 1->2->3->3->4->4->5
输出: 1->2->5

public ListNode deleteDuplicates(ListNode head) {
       if (head == null || head.next == null) {
            return head;
        }
        ListNode result = new ListNode(-1);
        result.next = head;
        ListNode slow = result;
        ListNode fast = result.next;
        while (fast != null) {
            while (fast.next != null && slow.next.val == fast.next.val)
                fast = fast.next;
            if ( slow.next == fast)
                slow = fast;
            else {
                slow.next = fast.next;
            }
            fast = fast.next;
        }
        return result.next;
    }

采用快慢指针，快指针用来跳过链表中重复的元素，慢指针用来拼接链表