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 || head.next == null) return head;
        ListNode rt = head, prev = new ListNode(0), ans = prev;
        prev.next = head;
        int distinct = head.val+1;
        while(rt!= null){
            if(distinct == rt.val) {prev.next = rt.next; rt = prev.next;}
            else {distinct = rt.val; 
                if(rt.next != null && rt.next.val == distinct){prev.next = rt.next; rt = prev.next;}
                else{ prev = rt; rt = rt.next;}
            }
        }
        return ans.next;
    }
}