Reverse a Linked List in groups.java

class LinkedList 
{ 
    Node head;  // head of list 

    /* Linked list Node*/
    class Node 
    { 
        int data; 
        Node next; 
        Node(int d) {data = d; next = null; } 
    } 

    Node reverse(Node head, int k) 
    { 
       Node current = head; 
       Node next = null; 
       Node prev = null; 

       int count = 0; 

       /* Reverse first k nodes of linked list */
       while (count < k && current != null)  
       { 
           next = current.next; 
           current.next = prev; 
           prev = current; 
           current = next; 
           count++; 
       } 

       /* next is now a pointer to (k+1)th node  
          Recursively call for the list starting from current. 
          And make rest of the list as next of first node */
       if (next != null)  
          head.next = reverse(next, k); 

       // prev is now head of input list 
       return prev; 
    }                       


    /* Utility functions */

    /* Inserts a new Node at front of the list. */
    public void push(int new_data) 
    { 
        /* 1 & 2: Allocate the Node & 
                  Put in the data*/
        Node new_node = new Node(new_data); 

        /* 3. Make next of new Node as head */
        new_node.next = head; 

        /* 4. Move the head to point to new Node */
        head = new_node; 
    } 

    /* Function to print linked list */
    void printList() 
    { 
        Node temp = head; 
        while (temp != null) 
        { 
           System.out.print(temp.data+" "); 
           temp = temp.next; 
        }   
        System.out.println(); 
    } 

     /* Driver program to test above functions */
    public static void main(String args[]) 
    { 
        LinkedList llist = new LinkedList(); 

        /* Constructed Linked List is 1->2->3->4->5->6-> 
           7->8->8->9->null */
        llist.push(9); 
        llist.push(8); 
        llist.push(7); 
        llist.push(6); 
        llist.push(5); 
        llist.push(4); 
        llist.push(3); 
        llist.push(2); 
        llist.push(1); 

        System.out.println("Given Linked List"); 
        llist.printList(); 

        llist.head = llist.reverse(llist.head, 3); 

        System.out.println("Reversed list"); 
        llist.printList(); 
    } 
}