83. Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->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 == NULL){
13             return head;
14         }
15         
16         
17         ListNode* l1 = head;
18         
19         while(l1 && l1->next)
20         {
21             if(l1->val != l1->next->val){
22                 l1 = l1->next;
23             }else{
24                 ListNode* p = l1->next->next;
25                 l1->next = p;
26             }
27             
28         }
29         return head;
30     }
31 };