Remove Duplicates from Sorted List

 1 //Definition for singly-linked list.
 2  struct ListNode {
 3      int val;
 4      ListNode *next;
 5      ListNode(int x) : val(x), next(NULL) {}
 6  };
 7  
 8 class Solution {
 9 public:
10     ListNode *deleteDuplicates(ListNode *head) {
11         if(head==NULL) return NULL;
12         ListNode * index =head;
13         ListNode * p=head->next;
14         while(p){
15             if(index->val!=p->val){
16                 index=index->next;
17                 index->val=p->val;
18             }
19             p=p->next;
20         }
21         ListNode * del=index->next;
22         index->next=NULL;
23         while(del){
24             ListNode * tmp = del->next;
25             delete del;
26             del=del->next;
27         }
28         return head;
29     }
30 };