add 043-Multiply-Strings

Author: zongyanqi

043-Multiply-Strings.js

@@ -0,0 +1,46 @@
+/**
+ * https://leetcode.com/problems/multiply-strings/description/
+ * Difficulty:Medium
+ *
+ * Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2.
+ * Note:
+ * The length of both num1 and num2 is < 110.
+ * Both num1 and num2 contains only digits 0-9.
+ * Both num1 and num2 does not contain any leading zero.
+ * 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) {
+    var m = num1.length;
+    var n = num2.length;
+    var arr = new Array(m + n).fill(0);
+    for (var i = m - 1; i >= 0; i--) {
+        for (var j = n - 1; j >= 0; j--) {
+            var mul = (num1[i] - '0') * (num2[j] - '0');
+
+            var sum = mul + arr[i + j + 1];
+
+            arr[i + j] += Math.floor(sum / 10);
+            arr[i + j + 1] = sum % 10;
+        }
+    }
+
+    var str = arr.reduce((a, b) => {
+        if (a === '' && b === 0) return a;
+        return a + b;
+    }, '');
+
+    return str ? str : '0';
+
+};
+
+console.log(multiply('89', '45'));
+console.log(multiply('123', '123'));
+console.log(multiply('123', '0'));
+
+