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