Remove Duplicates from Sorted List

https://leetcode.com/problems/remove-duplicates-from-sorted-list/
 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         ListNode * temp=NULL;
13         ListNode * tail=NULL;
14         temp=head;
15         while(temp!=NULL)
16         {
17             if(tail!=NULL)
18             {
19                 if(tail->val==temp->val)
20                 {
21                     tail->next=temp->next;
22                     temp=tail->next;
23                 }
24                 else
25                 {
26                     tail=temp;
27                     temp=temp->next;
28                 }
29             }
30             else
31             {
32                 tail=temp;
33                 temp=temp->next;
34             }
35             
36 
37         }
38         return head;
39     }
40 };