82. 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 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* deleteDuplicates(ListNode* head) {
12         if(!head){
13             return head;
14         }
15         
16         ListNode* newHead = new ListNode(-1);
17         newHead->next = head;
18         
19         ListNode* prev = newHead;
20         ListNode* p = head;
21         
22         while(p && p->next){
23             
24             if(p->val != p->next->val){
25                 prev = p;
26                 p = p->next;
27             }else{
28                 int val = p->val;
29                 ListNode* n = p->next->next;
30                 while(n){
31                     if(n->val != val){
32                         break;
33                     }
34                     n = n->next;
35                 }
36                 prev->next = n;
37                 p = n;
38             }
39         }
40         return newHead->next;
41     }
42 };