Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given

1->2->3->3->4->4->5

, return

1->2->5

.
Given

1->1->1->2->3

, return

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||head->next==NULL)
return head;
ListNode *dummy=new ListNode(0);
dummy->next=head;
ListNode *p=dummy,*tmp;
while(p->next!=NULL)
{
if(p->next->next!=NULL)
{
if(p->next->val==p->next->next->val)
{
while(p->next->val==p->next->next->val)
{
tmp=p->next->next->next;
p->next->next=tmp;
if(p->next->next==NULL)
break;
}
tmp=p->next->next;
p->next=tmp;
continue;
}
}

p=p->next;
if(p==NULL)
break;

}
return dummy->next;
}
};