LeetCode83 - Remove Duplicates from Sorted List--删除有序链表中重复的元素

/**
 * 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 NULL;
       ListNode* p1=head;
       ListNode* p2=head->next;
       while(p2!= NULL)
       {
          while(p2!=NULL && p1->val == p2->val)
              p2=p2->next;
           if(p2==NULL)
               p1->next = NULL;
           else
           {
               p1->next = p2;
               p1=p2;
               p2=p2->next;
           }
       }
       return head;
    }
};