var assert = require('assert');

​

function swapEveryTwo(head) {

  // Fill in this method

  return head;

}

​

function Node(val) {

  this.val = val;

  this.next = null;

}

​

function LinkedListNode(val) {

  this.val = val;

  this.next = null;

}

​

var list1 = new LinkedListNode(3);

var nodes1 = [4, 5, 6, 7, 8, 9, 10];

createNodes(list1, nodes1);

​

var list2 = new LinkedListNode(1);

var nodes2 = [2, 3, 4, 5, 6, 7, 8];

createNodes(list2, nodes2);

​

function createNodes(head, nodes) {

  for (let i = 0; i < nodes.length; i++) {