Leetcode -- Remove Duplicates from Sorted List

/**  
  * Definition for singly-linked list.  
  * struct ListNode {  
  *   int val;  
  *   ListNode *next;  
  *   ListNode(int x) : val(x), next(NULL) {}  
  * };  
  */  
 class Solution {  
 public:  
   ListNode *deleteDuplicates(ListNode *head) {  
     if(head == NULL) {  
       return head;  
     }  
     ListNode * prev = head;  
     ListNode * curr = head->next;  
     while(curr != NULL) {  
       if(prev->val == curr->val) {  
         prev->next = curr->next;  
         curr->next = NULL;  
         delete curr;  
         curr = prev->next;  
       } else {  
         prev = curr;  
         curr = curr->next;  
       }  
     }  
     return head;  
   }  
 };