2. Add Two Numbers.js

/**
 * You are given two non-empty linked lists representing two non-negative integers.
 * The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
 * You may assume the two numbers do not contain any leading zero, except the number 0 itself.
 */

/**
 * Example
 * Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
 *  Output: 7 -> 0 -> 8
 * Explanation: 342 + 465 = 807.
 */

/**
* Hints:
* Iterate
*/

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function(l1, l2) {
  const ro = [];

  const add = (l1, l2, carry) => {
    if (l1 !== null || l2 !== null || carry !== 0) {
      const val = (l1 ? l1.val : 0) + (l2 ? l2.val : 0) + carry;
      ro.push(val % 10);
      return add(l1 ? l1.next : null, l2 ? l2.next : null, Math.floor(val / 10));
    }
  }

  add(l1, l2, 0, []);

  return ro;
};