Javascript Program To Merge A Linked List Into Another Linked List At Alternate Positions

// Javascript program to merge a linked list 
// into another at alternate positions 

// A nexted list node 
class Node {
    constructor() {
        this.data = 0;
        this.next = null;
    }
};

/* Function to insert a node at 
   the beginning */
function push(head_ref, new_data) {
    let new_node = new Node();
    new_node.data = new_data;
    new_node.next = (head_ref);
    (head_ref) = new_node;
    return head_ref;

}

/* Utility function to print a 
   singly linked list */
function printList(head) {
    let temp = head;
    while (temp != null) {
        console.log(temp.data + " ");
        temp = temp.next;
    }
}

// Main function that inserts nodes of 
// linked list q into p at alternate 
// positions. Since head of first list 
// never changes and head of second list 
// may change, we need single pointer for 
// first list and double pointer for second 
// list. 
function merge(p, q) {
    let p_curr = p, q_curr = q;
    let p_next, q_next;

    // While there are available positions 
    // in p 
    while (p_curr != null &&
        q_curr != null) {
        // Save next pointers 
        p_next = p_curr.next;
        q_next = q_curr.next;

        // Make q_curr as next of p_curr 
        // Change next pointer of q_curr 
        q_curr.next = p_next;

        // Change next pointer of p_curr 
        p_curr.next = q_curr;

        // Update current pointers for next 
        // iteration 
        p_curr = p_next;
        q_curr = q_next;
    }

    // Update head pointer of second list
    q = q_curr;
    return q;
}

// Driver code 
let p = null, q = null;
p = push(p, 3);
p = push(p, 2);
p = push(p, 1);
console.log(
    "First Linked List:");
printList(p);
q = push(q, 8);
q = push(q, 7);
q = push(q, 6);
q = push(q, 5);
q = push(q, 4);
console.log(
    "Second Linked List:");
printList(q);
q = merge(p, q);
console.log(
    "Modified First Linked List:");
printList(p);
console.log(
    "Modified Second Linked List:");
printList(q);
// This code is contributed by rrrtnx.