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;
}
};