Reverse Nodes in k-Group

 https://leetcode.com/problems/reverse-nodes-in-k-group/

class Solution {
public:
    ListNode* reverseKGroup(ListNode* head, int k) {
        if(head ==NULL || k==1) return head;
        ListNode* dummy = new ListNode(0);
        dummy->next=head;
        ListNode* cur=dummy, *nex=dummy ,*pre=dummy;
        int count=0;
        while(cur->next!=NULL){
            cur=cur->next;
            count++;
        }
        while(count>=k){
            cur=pre->next;
            nex=cur->next;
            for(int i=1;i<k;i++)
            {
               cur->next=nex->next;
                nex->next=pre->next;
                pre->next=nex;
                nex=cur->next;
            }
            pre=cur;
            count-=k;
        }
        return dummy->next;
    }
};