Reverse Nodes in k-Group

class Solution {
public:
    ListNode* reverseKGroup(ListNode* head, int k) {
        if(k < 2) {
            return head;
        }
        ListNode *result = new ListNode(0);
        result->next = head;
        ListNode *cur = head, *start = head, *nextP, *preP = result, *head2, *tail;
        int count = 0;
        while(cur) {
            count ++;
            if(count == 1) {
                //Record the start point of every son list.
                head2 = preP;
                start = cur;
                preP = cur;
                if(cur) {
                    cur = cur->next;
                }
            }
            else if(count == k) {
                //Record the next point of every son lists.
                tail = cur->next;
                cur = start->next;
                preP = start;
                nextP = cur->next;
                while(count > 1) {
                    cur->next = head2->next;
                    head2->next = cur;
                    preP->next = nextP;
                    cur = nextP;
                    if(nextP) {
                        nextP = nextP->next;
                    }
                    count --;
                }
                count = 0;
            }
            else {
                preP = cur;
                if(cur) {
                    cur = cur->next;
                }
            }
        }
        return result->next;
    }
};