add Easy_415_Add_Strings

Author: zongyanqi

Easy_415_Add_Strings.js

@@ -0,0 +1,37 @@
+/**
+ * Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.
+ * Note:
+ *
+ * The length of both num1 and num2 is < 5100.
+ * 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 addStrings = function (num1, num2) {
+    var carry = 0;
+    var len1 = num1.length;
+    var len2 = num2.length;
+    var forCount = Math.max(len1, len2);
+    var newNum = '';
+    for (var i = 0; i < forCount; i++) {
+        var a = parseInt(num1[len1 - 1 - i]) || 0;
+        var b = parseInt(num2[len2 - 1 - i]) || 0;
+        var c = a + b + carry;
+        carry = Math.floor(c / 10);
+        var e = c % 10;
+        newNum = e + newNum;
+    }
+
+    if (carry) {
+        newNum = carry + newNum
+    }
+    return newNum;
+};
+
+console.log(addStrings('12', '123') == '135');