Remove Duplicates from Sorted List

 1 class Solution {
 2 public:
 3     ListNode* deleteDuplicates(ListNode* head) {
 4         ListNode prehead(0);
 5         prehead.next=head;
 6         ListNode *pre=&prehead;
 7         while(head)
 8         {
 9             if(head&&head->next&&head->val==head->next->val)
10             {
11                 while(head&&head->next&&head->val==head->next->val)head=head->next;
12                 pre->next=head;
13             }
14             else
15             {
16                 pre=head;
17                 head=head->next;
18             }
19             
20         }
21         return prehead.next;
22         
23     }
24 };