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.

 1 class Solution {
 2 public:
 3     ListNode *deleteDuplicates(ListNode *head) {
 4         return deleteDuplicates_1(head);
 5     }
 6     
 7     ListNode *deleteDuplicates_1(ListNode *head) {
 8         ListNode dummy(0), *cur = &dummy;
 9         dummy.next = head;
10         while (cur->next)
11         {
12             ListNode *node = cur->next;
13             int val = node->val;
14             if (!node->next || node->next->val != val) {
15                 cur = cur->next;
16                 continue;
17             }
18             while (node && node->val == val) {
19                 ListNode *del = node;
20                 node = node->next;
21                 delete del;
22             }
23             cur->next = node;
24         }
25         return dummy.next;
26     }
27     
28     ListNode *deleteDuplicates_2(ListNode *head) {
29         if (!head) return NULL;
30         if (!head->next || head->val != head->next->val) {
31             head->next = deleteDuplicates(head->next);
32             return head;
33         }
34         int val = head->val;
35         while(head && head->val == val) {
36             ListNode *del = head;
37             head = head->next;
38             delete del;
39         }
40         return deleteDuplicates(head);
41     }
42 };