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.

Solution

/**
 * 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 dummyNode = new ListNode(1);
        dummyNode.next = head;

        ListNode prev = dummyNode;
        ListNode cur = head;

        while (cur != null) {
            while (cur.next != null && cur.val == cur.next.val) {
                cur = cur.next;
            }

            if (prev.next == cur) {
                prev = prev.next;
            } else {
                prev.next = cur.next;
            }

            cur = cur.next;
        }

        return dummyNode.next;
    }
}