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Javascript Program For Reversing A Linked List In Groups Of Given Size- Set 2

  • Last Updated : 19 Jan, 2022

Given a linked list, write a function to reverse every k nodes (where k is an input to the function). 
Examples:

Input: 1->2->3->4->5->6->7->8->NULL and k = 3 
Output: 3->2->1->6->5->4->8->7->NULL. 

Input: 1->2->3->4->5->6->7->8->NULL and k = 5
Output: 5->4->3->2->1->8->7->6->NULL.

We have already discussed its solution in below post 
Reverse a Linked List in groups of given size | Set 1
In this post, we have used a stack which will store the nodes of the given linked list. Firstly, push the k elements of the linked list in the stack. Now pop elements one by one and keep track of the previously popped node. Point the next pointer of prev node to top element of stack. Repeat this process, until NULL is reached.
This algorithm uses O(k) extra space.

Javascript




<script>
// Javascript program to reverse a linked list
// in groups of given size
class GfG
{
    // Link list node
    class Node
    {
        constructor()
        {
            this.data = 0;
            this.next = null;
        }
     }
 
    var head = null;
 
    /* Reverses the linked list in groups of
       size k and returns the pointer to the new head node. */
    function Reverse(head, k)
    {
        // Create a stack of Node*
        var mystack = [];
        var current = head;
        var prev = null;
 
        while (current != null)
        {
            // Terminate the loop whichever comes
            // first either current == NULL or
            // count >= k
            var count = 0;
            while (current != null && count < k)
            {
                mystack.push(current);
                current = current.next;
                count++;
            }
 
            // Now pop the elements of stack one
            // by one
            while (mystack.length > 0)
            {
                // If final list has not been
                // started yet.
                if (prev == null)
                {
                    prev = mystack.pop();
                    head = prev;
                     
                }
                else
                {
                    prev.next = mystack.pop();
                    prev = prev.next;
                     
                }
            }
        }
 
        // Next of last element will point
        // to NULL.
        prev.next = null;
 
        return head;
    }
 
    // UTILITY FUNCTIONS
    // Function to push a node
    function push(new_data)
    {
        // Allocate node
        var new_node = new Node();
 
        // Put in the data
        new_node.data = new_data;
 
        // Link the old list off the
        // new node
        new_node.next = head;
 
        // Move the head to point to the
        // new node
        head = new_node;
    }
 
    // Function to print linked list
    function printList(node)
    {
        while (node != null)
        {
            document.write(node.data + " ");
            node = node.next;
        }
    }
}
     
// Driver code
     
// Start with the empty list
// Node head = null;
 
/* Created Linked list is
   1->2->3-> 4->5->6->7->8->9 */
push(9);
push(8);
push(7);
push(6);
push(5);
push(4);
push(3);
push(2);
push(1);
 
document.write("Given linked list <br/>");
printList(head);
head = Reverse(head, 3);
document.write("<br/>");
 
document.write("Reversed Linked list <br/>");
printList(head);
// This code contributed by aashish1995
</script>

Output: 

Given Linked List
1 2 3 4 5 6 7 8 9 
Reversed list
3 2 1 6 5 4 9 8 7

Please refer complete article on Reverse a Linked List in groups of given size | Set 2 for more details!
 


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