Javascript Program For QuickSort On Singly Linked List

QuickSort on Doubly Linked List is discussed here. QuickSort on Singly linked list was given as an exercise. The important things about implementation are, it changes pointers rather swapping data and time complexity is same as the implementation for Doubly Linked List.

In partition(), we consider last element as pivot. We traverse through the current list and if a node has value greater than pivot, we move it after tail. If the node has smaller value, we keep it at its current position. 

In QuickSortRecur(), we first call partition() which places pivot at correct position and returns pivot. After pivot is placed at correct position, we find tail node of left side (list before pivot) and recur for left list. Finally, we recur for right list.

Javascript

<script>
// Javascript program for Quick Sort on
// Singly LinKed List

// Sort a linked list using quick sort
class Node
{
    constructor(val)
    {
        this.data = val;
        this.next = null;
    }
}

var head;

function addNode(data)
{
    if (head == null)
    {
        head = new Node(data);
        return;
    }

    var curr = head;
    while (curr.next != null)
        curr = curr.next;

    var newNode = new Node(data);
    curr.next = newNode;
}

function printList(n)
{
    while (n != null)
    {
        document.write(n.data);
        document.write(" ");
        n = n.next;
    }
}

// Takes first and last node,
// but do not break any links in
// the whole linked list
function partitionLast(start, end)
{
    if (start == end ||
        start == null ||
        end == null)
        return start;

    var pivot_prev = start;
    var curr = start;
    var pivot = end.data;

    // Iterate till one before the end,
    // no need to iterate till the end
    // because end is pivot
    while (start != end)
    {
        if (start.data < pivot)
        {
            // Keep tracks of last modified
            // item
            pivot_prev = curr;
            var temp = curr.data;
            curr.data = start.data;
            start.data = temp;
            curr = curr.next;
        }
        start = start.next;
    }

    // Swap the position of curr i.e.
    // next suitable index and pivot
    var temp = curr.data;
    curr.data = pivot;
    end.data = temp;

    // Return one previous to current
    // because current is now pointing
    // to pivot
    return pivot_prev;
}

function sort(start, end)
{
    if (start == null ||
        start == end ||
        start == end.next)
            return;

    // Split list and partition recurse
    var pivot_prev = partitionLast(start, end);
    sort(start, pivot_prev);

    // If pivot is picked and moved to the start,
    // that means start and pivot is same
    // so pick from next of pivot
    if (pivot_prev != null &&
        pivot_prev == start)
        sort(pivot_prev.next, end);

    // If pivot is in between of the list,
    // start from next of pivot,
    // since we have pivot_prev, so we move two nodes
    else if (pivot_prev != null &&
             pivot_prev.next != null)
        sort(pivot_prev.next.next, end);
}

// Driver Code
addNode(30);
addNode(3);
addNode(4);
addNode(20);
addNode(5);

var n = head;
while (n.next != null)
    n = n.next;

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

sort(head, n);

document.write(
         "<br/>Linked List after sorting<br/>");
printList(head);
// This code is contributed by umadevi9616
</script>

Output:

Linked List before sorting 
30 3 4 20 5 
Linked List after sorting 
3 4 5 20 30 

Please refer complete article on QuickSort on Singly Linked List for more details!