Remove Duplicates from Sorted List II [LeetCode]

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:

 1     ListNode *deleteDuplicates(ListNode *head) {
 2         if(head == NULL || head->next == NULL)
 3             return head;
 4         
 5         //remove the head 
 6         ListNode * same_node = NULL;
 7         while(head != NULL) {
 8             if(same_node == NULL) {
 9                 if(head->next != NULL && head->val == head->next->val){
10                     same_node = head; 
11                     head = head->next;
12                 }else {
13                     break;
14                 }
15             }else {
16                 if(head->val == same_node->val)
17                     head = head->next;
18                 else
19                     same_node = NULL;   
20             }
21         }
22           
23         if(head == NULL || head->next == NULL)
24             return head;  
25             
26         ListNode * pre = head;
27         ListNode * same = NULL; 
28         ListNode * current = pre->next;
29         while(current != NULL) {
30             if(same == NULL) {
31                if(current->next != NULL && current->val == current->next->val){
32                     same = current;
33                     pre->next = current->next;
34                 }else{
35                     pre = pre->next;
36                 }
37                 current = current->next;
38             }else {
39                 if(current->val == same->val){
40                     pre->next = current->next;
41                     current = current->next;
42                 }else {
43                     same = NULL;
44                 }
45             }
46         }
47         
48         return head;
49     }