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 contains a single digit. Add the two numbers and return the sum as a linked list.

// You may assume the two numbers do not contain any leading zero, except the number 0 itself.

// Example 1:

// Input: l1 = [2,4,3], l2 = [5,6,4] Output: [7,0,8] Explanation: 342 + 465 = 807.

// Example 2:

// Input: l1 = [0], l2 = [0] Output: [0]

// Example 3:

// Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9] Output: [8,9,9,9,0,0,0,1]

// Constraints:

// The number of nodes in each linked list is in the range [1, 100].

// 0 <= Node.val <= 9

// It is guaranteed that the list represents a number that does not have leading zeros.

// ​

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function (l1, l2) {
  let linkedList = new ListNode(0, null);
  let current = linkedList;
  let plus = 0;

  while (l1 !== null || l2 !== null) {
    let sum = plus;
    if (l1 !== null) {
      sum += l1.val;
      l1 = l1.next;
    }
    if (l2 !== null) {
      sum += l2.val;
      l2 = l2.next;
    }
    if (10 <= sum) {
      sum -= 10;
      plus = 1;
    } else plus = 0;
    current.next = new ListNode(sum, null);
    current = current.next;
  }
  if (plus > 0) {
    current.next = new ListNode(plus, null);
  }
  return linkedList.next;
};