Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

 

public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head==null || head.next==null) return head;
        ListNode safe = new ListNode(-1);
        safe.next = head;
        ListNode pre = safe;
        ListNode cur = head;
        ListNode post = head.next;
        while(post!=null){
            if(post.val==cur.val){
                while(post!=null && post.val==cur.val){
                    cur = post;
                    post = post.next;
                }
                cur = post;
                if(post!=null)
                    post = post.next;
                continue;
            }
             pre.next = cur;
             pre = cur;
             cur = post;
             if(post!=null)
                post = post.next;
        }
        pre.next = cur;
        return safe.next;
    }
}