Remove Duplicates from Sorted List

</pre><pre name="code" class="java">public class Solution {    public ListNode deleteDuplicates(ListNode head) {        if(head == null || head.next == null){            return head;        }                ListNode pre = head;        ListNode cur = head.next;        while(cur != null && pre != null){            if(cur.val == pre.val){                cur = cur.next;            }            else {                pre.next = cur;                pre = cur;                cur = cur.next;            }        }                if(cur == null){            pre.next = null;        }                return head;    }}

Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.