/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
       ListNode temp=new ListNode(0);
        temp.next=head;
        ListNode pre=temp;
        while (head!=null){
            while (head.next!=null&&head.val==head.next.val){
                    head=head.next;
            }
            if (pre.next==head){//no Duplicates
                pre=pre.next;
            }else {// has Duplicates
                pre.next = head.next;
            }
            head=head.next;
        }
        return temp.next;
    }
}