LeetCode - 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;}bool isDuplicate=false;ListNode *tmp=new ListNode(0);tmp->next=head;ListNode *p=tmp, *q=head,*r=head;while(q){r=q->next;while(r&&q->val==r->val){isDuplicate=true;r=r->next;}if(isDuplicate){isDuplicate=false;}else{p->next=q;p=q;}q=r;}p->next=q;//最后一组结点可能是重复结点head=tmp->next;delete tmp;tmp=NULL;return head;    }};