Add solution #43

Author: JoshCrozier

README.md

@@ -8,6 +8,7 @@
 |:---|:---|:---|
 4|[Median of Two Sorted Arrays](./0004-median-of-two-sorted-arrays.js)|Hard|
 36|[Valid Sudoku](./0036-valid-sudoku.js)|Medium|
+43|[Multiply Strings](./0043-multiply-strings.js)|Medium|
 58|[Length of Last Word](./0058-length-of-last-word.js)|Easy|
 67|[Add Binary](./0067-add-binary.js)|Easy|
 151|[Reverse Words in a String](./0151-reverse-words-in-a-string.js)|Medium|

solutions/0043-multiply-strings.js

@@ -0,0 +1,40 @@
+/**
+ * 43. Multiply Strings
+ * https://leetcode.com/problems/multiply-strings/
+ * Difficulty: Medium
+ *
+ * Given two non-negative integers num1 and num2 represented as strings,
+ * return the product of num1 and num2, also represented as a string.
+ *
+ * - The length of both num1 and num2 is < 110.
+ * - Both num1 and num2 contain only digits 0-9.
+ * - Both num1 and num2 do not contain any leading zero, except the number 0 itself.
+ * - You must not use any built-in BigInteger library or convert the inputs to integer directly.
+ */
+
+/**
+ * @param {string} num1
+ * @param {string} num2
+ * @return {string}
+ */
+var multiply = function(num1, num2) {
+  const result = new Array(num1.length + num2.length).fill(0);
+  for (let i = num1.length - 1; i >= 0; i--) {
+    for (let j = num2.length - 1; j >= 0; j--) {
+      const sum = num1[i] * num2[j] + result[i + j + 1];
+      result[i + j] += Math.floor(sum / 10);
+      result[i + j + 1] = sum % 10;
+    }
+  }
+  return result.join('').replace(/^0+(?!$)/, '');
+};
+
+// one-liner alternative that breaks the rules:
+/**
+ * @param {string} num1
+ * @param {string} num2
+ * @return {string}
+ */
+var multiply = function(num1, num2) {
+  return ((BigInt(num1) * BigInt(num2))).toString();
+};