Add solution #415

Author: JoshCrozier

README.md

@@ -185,6 +185,7 @@
 405|[Convert a Number to Hexadecimal](./0405-convert-a-number-to-hexadecimal.js)|Easy|
 412|[Fizz Buzz](./0412-fizz-buzz.js)|Easy|
 414|[Third Maximum Number](./0414-third-maximum-number.js)|Easy|
+415|[Add Strings](./0415-add-strings.js)|Easy|
 419|[Battleships in a Board](./0419-battleships-in-a-board.js)|Medium|
 435|[Non-overlapping Intervals](./0435-non-overlapping-intervals.js)|Medium|
 442|[Find All Duplicates in an Array](./0442-find-all-duplicates-in-an-array.js)|Medium|

solutions/0415-add-strings.js

@@ -0,0 +1,33 @@
+/**
+ * 415. Add Strings
+ * https://leetcode.com/problems/add-strings/
+ * Difficulty: Easy
+ *
+ * Given two non-negative integers, num1 and num2 represented as string, return the sum of num1 and
+ * num2 as a string.
+ *
+ * You must solve the problem without using any built-in library for handling large integers (such
+ * as BigInteger). You must also not convert the inputs to integers directly.
+ */
+
+/**
+ * @param {string} num1
+ * @param {string} num2
+ * @return {string}
+ */
+var addStrings = function(num1, num2) {
+  let result = '';
+
+  for (let i = num1.length - 1, j = num2.length - 1, carry = 0; i > -1 || j > -1 || carry === 1;) {
+    if (i > -1) {
+      carry += num1.charCodeAt(i--) - 48;
+    }
+    if (j > -1) {
+      carry += num2.charCodeAt(j--) - 48;
+    }
+    result = (carry % 10) + result;
+    carry = Math.floor(carry / 10);
+  }
+
+  return result;
+};