Remove duplicates from sorted list II

deleteDuplicates.java

public static ListNode deleteDuplicates(ListNode head) {
    if(head == null) return null;

    ListNode fake = new ListNode(-1);
    fake.next = head;

    ListNode pre = fake;
    ListNode cur = head;
    while(cur != null){
        while(cur.next != null && cur.val == cur.next.val){
            cur = cur.next;
        }
        if(pre.next == cur){
            pre = pre.next;
        }else{
            pre.next = cur.next;
        }
        cur = cur.next;
    }
    return fake.next;
}