Javascript Program For QuickSort On Singly Linked List

// 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;
    }
}

let head;

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

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

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

function printList(n) {
    while (n != null) {
        console.log(n.data);
        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;

    let pivot_prev = start;
    let curr = start;
    let 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;
            let 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
    let 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
    let 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);

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

console.log("Linked List before sorting");
printList(head);
sort(head, n);
console.log("Linked List after sorting");
printList(head);
// This code is contributed by umadevi9616