Javascript Program For Merge Sort For Doubly Linked List

// javascript program to implement merge sort in singly linked list

// Linked List Class

let head; // head of list

/* Node Class */
class Node {

    // Constructor to create a new node
    constructor(d) {
        this.data = d;
        this.next = this.prev = null;
    }
}

function print(node) {
    temp = node;
    console.log("Forward Traversal using next pointer");
    while (node != null) {
        console.log(node.data + " ");
        temp = node;
        node = node.next;
    }
    console.log("Backward Traversal using prev pointer");
    while (temp != null) {
        console.log(temp.data + " ");
        temp = temp.prev;
    }
}

// Split a doubly linked list (DLL) into 2 DLLs of
// half sizes
function split(head) {
    fast = head, slow = head;
    while (fast.next != null && fast.next.next != null) {
        fast = fast.next.next;
        slow = slow.next;
    }
    temp = slow.next;
    slow.next = null;
    return temp;
}

function mergeSort(node) {
    if (node == null || node.next == null) {
        return node;
    }
    let second = split(node);

    // Recur for left and right halves
    node = mergeSort(node);
    second = mergeSort(second);

    // Merge the two sorted halves
    return merge(node, second);
}

// Function to merge two linked lists
function merge(first, second) {
    // If first linked list is empty
    if (first == null) {
        return second;
    }

    // If second linked list is empty
    if (second == null) {
        return first;
    }

    // Pick the smaller value
    if (first.data < second.data) {
        first.next = merge(first.next, second);
        first.next.prev = first;
        first.prev = null;
        return first;
    } else {
        second.next = merge(first, second.next);
        second.next.prev = second;
        second.prev = null;
        return second;
    }
}

// Driver program to test above functions
head = new Node(10);
head.next = new Node(30);
head.next.next = new Node(3);
head.next.next.next = new Node(4);
head.next.next.next.next = new Node(20);
head.next.next.next.next.next = new Node(5);

node = null;
node = mergeSort(head);
console.log("Linked list after sorting :");
print(node);

// This code is contributed by umadevi9616