和24题差不多，用一个指针记录前一个节点，需要特判，若count结束后并不等于k则翻转回来

class Solution {
public:
    ListNode* reverseKGroup(ListNode* head, int k) {
    	ListNode *newHead = new ListNode(0);
    	ListNode *relativeHead = newHead;
    	ListNode *tail = newHead;
    	ListNode *p = head;
    	ListNode *pre = head;
    	int count = 0;
    	while(p) {
    		if(count == k || count == 0) {
    			relativeHead = tail;
    			tail = p;
    			count = 0;
    		}
    		pre = p;
    		p = p->next;
    		pre->next = relativeHead->next;
    		relativeHead->next = pre;
    		count++;
    	}
    	if(count != k){
    		p = relativeHead->next;
    		relativeHead->next = NULL;
    		while(p) {
    			pre = p;
    			p = p->next;
    			pre->next = relativeHead->next;
    			relativeHead->next = pre;
    		}
    	}
    	return newHead->next;      
    }
};

题目链接：https://leetcode-cn.com/problems/reverse-nodes-in-k-group/