Reverse a Linked List in groups of given size k, Java

Reverse a Linked List in groups of given size k

//'main' method must be in a class 'Rextester'.
//openjdk version '11.0.5'

import java.util.*;
import java.lang.*;

class Rextester
{  
    public static class Node
    {
      // public Node head;
        public int data;
        public Node next;
        
        public Node(int data)
        {
           this.data=data;
           this.next=null;
        } 
    }
  public static Node reverse(Node head, int x, int dup)
    {
       if (head == null)
           return null;
        Node prev=null;
        Node next=null;
        Node curr=head;
        dup=dup-x; //System.out.println(dup);
        int c=0; 
        while( dup >= x && c<x && curr!=null)
        {
            next=curr.next;
            curr.next=prev;
            prev=curr;
            curr=next;
            c++;
        }
       /*  while(curr!=null)
            {
                System.out.println(curr.data);
                curr=curr.next;
          }  */
        if(next!=null)
            head.next=reverse(next,x,dup);
        
        return prev;
    }
    public static void main(String args[])
    {
       Scanner sc=new Scanner(System.in);
        int t=sc.nextInt();
        while(t>0)
        {
            t--;
           int n=sc.nextInt();
           int x=sc.nextInt();
            Node head=null;
            int duplicate=n;
           // head.next=null;
            while(n>0)
            {
                 //System.out.println("1");
                n--;
                int tmp=sc.nextInt();
                Node ptr= new Node(tmp);
                ptr.next=null;
               // ptr=head;
               //  System.out.println(ptr.data);
                if(head == null)
                {
                   head=ptr;
                  // System.out.println(head.data);
                }
                else
                {
                  Node tmpp=head;
                    while( tmpp.next !=null)
                        tmpp=tmpp.next;
                    tmpp.next=ptr;
                    
                }
                
            }
        /*    while(head!=null)
            {
                System.out.println(head.data);
                head=head.next;
            }   */
            
           Node head2=reverse(head,x,duplicate);
            
            while(head2!=null)
            {
                System.out.println(head2.data);
                head2=head2.next;   
            }
                
        }
    }
}


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