/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
  public ListNode reverseKGroup(ListNode head, int k) {
        ListNode resHead = null;
        ListNode cur = head;
        int totalNodes = 0;
        while (cur != null) {
            cur = cur.next;
            totalNodes++;
        }
        cur = head;
        ListNode prevTail = null;
        int pNodes = 0;
        while (cur != null) {
            int ck = k;
            ListNode curTail = cur;
            ListNode prev = null;
            while (ck > 0 && cur != null) {
                pNodes++;
                ListNode next = cur.next;
                cur.next = prev;
                prev=cur;
                cur = next;
                ck--;
            }
            ListNode curHead = prev;
            if (resHead == null) {
                resHead = curHead;

            }
            ListNode cr = curHead;
            while (cr!=null){
                System.out.println(cr.val);
                cr=cr.next;
            }
           // System.out.println("-----");

            if (prevTail != null) {
                prevTail.next = prev;
                prevTail = curTail;
                prevTail.next = null;
            }
            if (prevTail == null) {
                prevTail = curTail;
            }
            if (totalNodes - pNodes < k) {
                prevTail.next = cur;
                return resHead;
            }
        }
        return resHead;
    }
}