LeetCode - 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.

/** * 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 *p=head, *q=head;while(p){q=p->next;while(q&&p->val==q->val){q=q->next;}p->next=q;p=q;}        return head;    }};