Java Program For Reversing A Linked List In Groups Of Given Size - Set 1

// Java program to reverse a 
// linked list in groups of
// given size
class LinkedList
{
    // Head of list
    Node head; 

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

    Node reverse(Node head, int k)
    {
        if(head == null)
          return null;
        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 the 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 code
    public static void main(String args[])
    {
        LinkedList llist = new LinkedList();

        // Create 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();
    }
}
// This code is contributed by Rajat Mishra