Add_Two_Numbers.js

/*
Add Two Numbers
https://leetcode.com/problems/add-two-numbers/

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.
*/

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

/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */

var addTwoNumbers = function (l1, l2) {
  if (l1 === null) return l2 === null ? new ListNode(0) : l2;
  else if (l2 === null) return l1;

  var elem = l1.val + l2.val;
  var number = new ListNode(elem % 10);
  var carry = elem >= 10 ? 1 : 0;
  l1 = l1.next;
  l2 = l2.next;

  const head = number;
  while (l1 !== null || l2 !== null) {
    elem = carry;
    if (l1 !== null) {
      elem += l1.val;
      l1 = l1.next;
    }
    if (l2 !== null) {
      elem += l2.val;
      l2 = l2.next;
    }

    number.next = new ListNode(elem % 10);
    number = number.next;
    carry = elem >= 10 ? 1 : 0;
  }
  if (carry === 1) number.next = new ListNode(1);
  return head;
};

module.exports.addTwoNumbers = addTwoNumbers;