LeetCode 25. Reverse Nodes in k-Group

#include <iostream>#include <vector>using namespace std;struct ListNode {  int val;  ListNode* next;  ListNode(int x) : val(x), next(NULL) {}};// set up a linked list and then reverse it in K-length group.ListNode* setUpLinkList() {  ListNode* newHead = new ListNode(0);  ListNode* current = newHead;  for(int i = 1; i < 6; ++i) {    ListNode* tmp = new ListNode(i);    current->next = tmp;    current = tmp;  }  return newHead;}void printList(ListNode* head) {  ListNode* tmp = head;  while(tmp) {    cout << tmp->val << " ";    tmp = tmp->next;  }  cout << endl;}ListNode* reverse(ListNode* prev, ListNode* end) {  ListNode* last = prev->next;  ListNode* curr = last->next;  while(curr != end) {    last->next = curr->next;    curr->next = prev->next;    prev->next = curr;    curr = last->next;  }  return last;}// reverse the linklist in 3-length.ListNode* reverseKLength(ListNode* head, int k) {  ListNode* dummy = new ListNode(0);  dummy->next = head;  int count = 0;  ListNode* prev = dummy;  while(head) {    count++;    if(count % k == 0) {      prev = reverse(prev, head->next);      head = prev->next;    } else {      head = head->next;    }  }  return dummy->next;}int main(void) {  ListNode* head = setUpLinkList();  printList(head);  ListNode* tmp = reverseKLength(head, 3);  printList(tmp);}