Remove Duplicates from Sorted List II

public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(head == null || head.next == null)
            return head;
        ListNode fakehead = new ListNode(-1);
        fakehead.next = head;
        ListNode runner = head;
        ListNode prerunner = fakehead;
        boolean isDup = false;
        int tmp = 0;
        while(runner!=null){
            if(!isDup){
                if(runner.next!=null && runner.val == runner.next.val){
                    tmp = runner.val;
                    isDup = true;
                    runner = runner.next;
                    prerunner.next = runner;
                }
                else{
                    runner = runner.next;
                    prerunner = prerunner.next;
                }
            }
            else{
                if(runner.val == tmp){
                    runner = runner.next;
                    prerunner.next = runner;
                }
                else{
                    isDup = false;
                }
            }
        }
        
        prerunner.next = null;
        return fakehead.next;
    }
}