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 ListNode *deleteDuplicates(ListNode *head) {
 2     // Start typing your C/C++ solution below
 3     // DO NOT write int main() function
 4     if(head==NULL || head->next==NULL)
 5         return head;
 6     ListNode * p = head;
 7      8     while(p->next!=NULL && p->val == p->next->val){
 9         p=p->next;
10     }
11 
12     if(p!=head){
13         while(head!=p->next)
14         {
15             ListNode * tmp = head;
16             head=head->next;
17             free(tmp);
18         }
19 
20         return deleteDuplicates(p->next);
21     }
22 
23     head->next=deleteDuplicates(head->next);
24     return head;
25 }