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.

Have you met this question in a real interview? 

Yes

Example

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

/**
 * Definition for ListNode
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param ListNode head is the head of the linked list
     * @return: ListNode head of the linked list
     */
    public static ListNode deleteDuplicates(ListNode head) {
        // write your code here
        ListNode pre = new ListNode(0);
        ListNode dummy = pre;
        while(head != null){
            boolean repeating = false;
            while(head.next != null && head.val == head.next.val){
                head = head.next;
                repeating = true;
            }
            pre.next = repeating ? head.next : head;
            pre = repeating ? pre : pre.next;
            head = head.next;
        }
        return dummy.next;
    }
}