LeetCode-Reverse Nodes in k-Group

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *reverseKGroup(ListNode *head, int k) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if (head == NULL || head->next == NULL || k <= 1)
{
return head;
}
ListNode *newHead = head;
ListNode *q = head;    ////目前要翻转的结点
ListNode *p = NULL;    //目前要翻转的结点的下一个结点
ListNode *pNext = NULL;    //p的下一个结点
ListNode *pEnd = q;    //用于探测剩余结点是够k个
ListNode *pPreEnd = NULL;    //目前已翻转的子链表中的最后一个结点
ListNode *pBeg = NULL;    //当前要翻转的k的结点的第一个结点，亦为翻转后的最后一个结点
while(true)
{
//剩余结点是否够k个
for (int i = 0; i < k - 1; ++i)
{
if (pEnd != NULL)
{
pEnd = pEnd->next;
}
else
{
break;
}
}
if (pEnd == NULL)
{
break;
}
//初始化p, pBeg
p = q->next;
pBeg = q;
//依次翻转k个相邻结点，注意保存p的下一个结点
for (int i = 0; i < k - 1; ++i)
{
pNext = p->next;
p->next = q;
q = p;
p = pNext;
}
//更新pPreEnd, q, pEnd
if (pPreEnd != NULL)
{
pPreEnd->next = q;
}
else
{
newHead = q;
}
pPreEnd = pBeg;
q = p;
pEnd = q;
pPreEnd->next = q;
}
return newHead;
}
};