2.add-two-numbers.md

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.

JavaScript

/**
 * 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 before = new ListNode();
  let tail = before;
  let c = 0;

  while (l1 || l2 || c) {
    const v1 = l1 ? l1.val : 0;
    const v2 = l2 ? l2.val : 0;
    const v = v1+v2+c;

    tail.next = new ListNode(v%10);
    tail = tail.next;
    c = v >= 10 ? 1 : 0;
    l1 = l1!==null ? l1.next : null;
    l2 = l2!==null ? l2.next : null;
  }

  return before.next;
};