Javascript Program For Recursive Selection Sort For Singly Linked List – Swapping Node Links

Given a singly linked list containing n nodes. The problem is to sort the list using the recursive selection sort technique. The approach should be such that it involves swapping node links instead of swapping node data.  

Examples:

Input: 10 -> 12 -> 8 -> 4 -> 6
Output: 4 -> 6 -> 8 -> 10 -> 12 

In Selection Sort, we first find the minimum element, swap it with the beginning node and recur for the remaining list. Below is the recursive implementation of these steps for the linked list. 

recurSelectionSort(head)
     if head->next == NULL
         return head
     Initialize min = head
     Initialize beforeMin = NULL
     Initialize ptr = head
    
     while ptr->next != NULL 
         if min->data > ptr->next->data
         min = ptr->next
         beforeMin = ptr
     ptr = ptr->next    
    
     if min != head
         swapNodes(&head, head, min, beforeMin)
    
     head->next = recurSelectionSort(head->next)
     return head

swapNodes(head_ref, currX, currY, prevY)
     head_ref = currY
     prevY->next = currX

     Initialize temp = currY->next
     currY->next = currX->next
     currX->next  = temp    

The swapNodes(head_ref, currX, currY, prevY) is based on the approach discussed here but it has been modified accordingly for the implementation of this post. 

Javascript

<script>
// Javascript implementation of recursive
// selection sort for singly linked list
// | Swapping node links

// A Linked list node
class Node
{
    constructor(val)
    {
        this.data = val;
        this.next = null;
    }
}

// Function to swap nodes 'currX' and
// 'currY' in a linked list without
// swapping data
function swapNodes(head_ref, currX,
                   currY,  prevY)
{
    // Make 'currY' as new head
    head_ref = currY;

    // Adjust links
    prevY.next = currX;

    // Swap next pointers
    var temp = currY.next;
    currY.next = currX.next;
    currX.next = temp;
    return head_ref;
}

// Function to sort the linked list using
// recursive selection sort technique
function recurSelectionSort(head)
{
    // If there is only a single node
    if (head.next == null)
        return head;

     // 'min' - pointer to store the node
     // having minimum data value
     var min = head;

     // 'beforeMin' - pointer to store node
     // previous to 'min' node
     var beforeMin = null;
     var ptr;

     // Traverse the list till the last node
     for (ptr = head; ptr.next != null;
          ptr = ptr.next)
     {
         // if true, then update 'min' and
         // 'beforeMin'
         if (ptr.next.data < min.data)
         {
             min = ptr.next;
             beforeMin = ptr;
         }
     }

     // if 'min' and 'head' are not same,
     // swap the head node with the 'min' node
     if (min != head)
         head = swapNodes(head, head,
                          min, beforeMin);

     // recursively sort the remaining list
     head.next = recurSelectionSort(head.next);

     return head;
}

// Function to sort the given linked list
function sort(head_ref)
{
    // If list is empty
    if ((head_ref) == null)
        return null;

    // Sort the list using recursive
    // selection sort technique
    head_ref = recurSelectionSort(head_ref);
    return head_ref;
}

// Function to insert a node at the
// beginning of the linked list
function push(head_ref, new_data)
{
    // Allocate node
    var new_node = new Node();

    // Put in the data
    new_node.data = new_data;

    // Link the old list to the
    // new node
    new_node.next = (head_ref);

    // Move the head to point to the
    // new node
    (head_ref) = new_node;
    return head_ref;
}

// Function to print the linked list
function printList(head)
{
    while (head != null)
    {
        document.write(head.data + " ");
        head = head.next;
    }
}

// Driver code
var head = null;

// Create linked list 10.12.8.4.6
head = push(head, 6);
head = push(head, 4);
head = push(head, 8);
head = push(head, 12);
head = push(head, 10);

document.write(
"Linked list before sorting:<br/>");
printList(head);

// Sort the linked list
head = sort(head);

document.write(
"<br/>Linked list after sorting:<br/>");
printList(head);
// This code is contributed by todaysgaurav
</script>

Output:

Linked list before sorting:
10 12 8 4 6
Linked list after sorting:
4 6 8 10 12

Time Complexity: O(n²)

Auxiliary Space: O(n)

Please refer complete article on Recursive selection sort for singly linked list | Swapping node links for more details!