[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) {
        
        ListNode *p = NULL,*q;
        
        if(head == NULL || head->next == NULL)
            return head;
            
        p = head;
        
        while(p!=NULL && p->next !=NULL){
            if(p->next->val == p->val){
                q = p->next->next;
                //Delete p->next;    //不需要的指针不删除吗？提示‘Delete‘ was not declared in this scope                p->next = q;
            }else{
                p = p->next;
            }//end if   
        }//end while
        return head;
    }
};