Add Two Numbers

https://leetcode.com/problems/add-two-numbers/description/

function ListNode(val) {
  this.val = val;
  this.next = null;
}

function getLinkedListFromArray(arr) {
  const list = new ListNode(0);
  let current = list;
  for (let el of arr) {
    current.next = new ListNode(el);
    current = current.next;
  }

  return list.next;
}

function printLinkedList(head) {
  const result = [];

  while (head !== null) {
    result.push(head.val);
    head = head.next;
  }

  console.log(result.join(' -> '));
}

function addTwoLists(a, b) {
  let carry = 0;
  let sum = 0;
  const head = new ListNode(0);
  let now = head;

  while (a !== null || b !== null) {
    sum = (a ? a.val : 0) + (b ? b.val : 0) + carry;
    carry = Math.floor(sum / 10);
    now.next = new ListNode(sum % 10);
    now = now.next;

    a = a ? a.next : null;
    b = b ? b.next : null;
  }

  if (carry) now.next = new ListNode(carry);
  return head.next;
}

const l1 = getLinkedListFromArray([1, 2, 3]); // 1 -> 2 -> 3
const l2 = getLinkedListFromArray([2, 3]); // 2 -> 3

printLinkedList(addTwoLists(l1, l2)); // 3 -> 5 -> 3