reverse linked list II

 ListNode* reverseBetween(ListNode* head, int m, int n) {
        if(m==n)return head;
        n-=m;
        ListNode*tmp=new ListNode(0);
        tmp->next=head;
        ListNode*pre=tmp,*cur;

        while(--m)pre=pre->next;

        cur=pre->next;
        ListNode*next=cur->next;
        while(n--)
        {
            next=cur->next;
            cur->next=next->next;
            next->next=pre->next;
            pre->next=next;
        }
        return tmp->next;
    }