leetcode--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.

/**
 * 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) {
		if(head==null) return null;
		ListNode pre = new ListNode(Integer.MAX_VALUE);
		pre.next = head;
		ListNode h = pre;
		ListNode cur = head;
		ListNode last = head.next;
		boolean found = false;
		while(last!=null){
			while(last!=null&&last.val==cur.val){
				last = last.next;
				found = true;
			}
			if(found){
				pre.next = last;
			}else{
				pre = cur;
				
			}		
			cur = last;
			if(last!=null) last=last.next;
			found = false;
		}
		return h.next;
    }
}