Rearrange a Linked List in Zig-Zag fashion

<script>

// Javascript program to arrange
// linked list in zigzag fashion

    /* Link list Node */
     class Node {
            constructor() {
                this.data = 0;
                this.next = null;
            }
        }

    var head = null;
    var temp = 0;

    // This function distributes
    // the Node in zigzag fashion
    function zigZagList(head) {
        // If flag is true, then
        // next node should be greater
        // in the desired output.
        var flag = true;

        // Traverse linked list starting from head.
        var current = head;
        while (current != null && current.next != null) {
            if (flag == true) /* "<" relation expected */
            {
                /*
                 * If we have a situation like A > B > C
                 where A, B and C are consecutive Nodes
                 * in list we get A > B < C by swapping B and C
                 */
                if (current.data > current.next.data) {
                    temp = current.data;
                    current.data = current.next.data;
                    current.next.data = temp;
                }
            } else /* ">" relation expected */
            {
                /*
                 * If we have a situation like A < B < C 
                 where A, B and C are consecutive Nodes
                 * in list we get A < C > B by swapping B and C
                 */
                if (current.data < current.next.data) {
                    temp = current.data;
                    current.data = current.next.data;
                    current.next.data = temp;
                }
            }

            current = current.next;

            /* flip flag for reverse checking */
            flag = !(flag);
        }
    }

    /* 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 of 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;
        }
        document.write("NULL<br/>");
    }

    /* Driver code */
    
        /* Start with the empty list */
        // Node head = null;

        // create a list 4 -> 3 -> 7 -> 8 -> 6 -> 2 -> 1
        // answer should be -> 3 7 4 8 2 6 1
        push(1);
        push(2);
        push(6);
        push(8);
        push(7);
        push(3);
        push(4);

        document.write("Given linked list <br/>");
        printList(head);

        zigZagList(head);

        document.write("Zig Zag Linked list <br/>");
        printList(head);

// This code contributed by gauravrajput1

</script>

<script>
// javascript program for the above approach// Node class
class Node {
    constructor(val) {
        this.data = val;
        this.next = null;
    }
}

var head;

    // Print Linked List
     function printLL() {
var t = head;
        while (t != null) {
            document.write(t.data + " ->");
            t = t.next;
        }
        document.write();
    }

    // Swap both nodes
     function swap(a,  b) {
        if (a == null || b == null)
            return;
        var temp = a.data;
        a.data = b.data;
        b.data = temp;
    }

    // Rearrange the linked list
    // in zig zag way
     function zigZag(node , flag) {
        if (node == null || node.next == null) {
            return node;
        }
        if (flag == 0) {
            if (node.data > node.next.data) {
                swap(node, node.next);
            }
            return zigZag(node.next, 1);
        } else {
            if (node.data < node.next.data) {
                swap(node, node.next);
            }
            return zigZag(node.next, 0);
        }
    }

    // Driver Code
    
        head = new Node(11);
        head.next = new Node(15);
        head.next.next = new Node(20);
        head.next.next.next = new Node(5);
        head.next.next.next.next = new Node(10);
        printLL();

        // 0 means the current element
        // should be smaller than the next
        var flag = 0;
        zigZag(head, flag);
        document.write("<br/>LL in zig zag fashion : <br/>");
        printLL();

// This code contributed by umadevi9616
</script>