Add solution #2

Author: JoshCrozier

README.md

@@ -7,6 +7,7 @@
 |#|Title|Difficulty|
 |:---|:---|:---|
 1|[Two Sum](./0001-two-sum.js)|Easy|
+2|[Add Two Numbers](./0002-add-two-numbers.js)|Medium|
 4|[Median of Two Sorted Arrays](./0004-median-of-two-sorted-arrays.js)|Hard|
 7|[Reverse Integer](./0007-reverse-integer.js)|Easy|
 27|[Remove Element](./0027-remove-element.js)|Easy|

solutions/0002-add-two-numbers.js

@@ -0,0 +1,43 @@
+/**
+ * 2. Add Two Numbers
+ * https://leetcode.com/problems/add-two-numbers/
+ * Difficulty: Medium
+ *
+ * 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.
+ */
+
+/**
+ * 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) {
+  const result = new ListNode();
+  let tail = result;
+  let carry = 0;
+
+  while (l1 || l2 || carry) {
+    const v1 = l1 ? l1.val : 0;
+    const v2 = l2 ? l2.val : 0;
+    const v = v1 + v2 + carry;
+
+    tail.next = new ListNode(v % 10);
+    tail = tail.next;
+    carry = v >= 10 ? 1 : 0;
+    l1 = l1 && l1.next;
+    l2 = l2 && l2.next;
+  }
+
+  return result.next;
+};