[LC] 82. 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.

Example 1:

Input: 1->2->3->3->4->4->5
Output: 1->2->5

Example 2:

Input: 1->1->1->2->3
Output: 2->3

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        
        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode cur = dummy;
        // check the next two node
        while(cur.next != null && cur.next.next != null) {
            if (cur.next.val == cur.next.next.val) {
                int num = cur.next.val;
                while(cur.next != null && cur.next.val == num) {
                    cur.next = cur.next.next;
                }
            } else {
                cur = cur.next;
            }
        }
        return dummy.next;
    }
}