Add solution #12

Author: JoshCrozier

README.md

@@ -13,6 +13,7 @@
 7|[Reverse Integer](./0007-reverse-integer.js)|Easy|
 8|[String to Integer (atoi)](./0008-string-to-integer-atoi.js)|Medium|
 10|[Regular Expression Matching](./0010-regular-expression-matching.js)|Hard|
+12|[Integer to Roman](./0012-integer-to-roman.js)|Medium|
 14|[Longest Common Prefix](./0014-longest-common-prefix.js)|Easy|
 17|[Letter Combinations of a Phone Number](./0017-letter-combinations-of-a-phone-number.js)|Medium|
 27|[Remove Element](./0027-remove-element.js)|Easy|

solutions/0012-integer-to-roman.js

@@ -0,0 +1,44 @@
+/**
+ * 12. Integer to Roman
+ * https://leetcode.com/problems/integer-to-roman/
+ * Difficulty: Medium
+ *
+ * Roman numerals are represented by seven different symbols: `I`, `V`, `X`, `L`, `C`, `D` and `M`.
+ *
+ * Symbol       Value
+ * I            1
+ * V            5
+ * X            10
+ * L            50
+ * C            100
+ * D            500
+ * M            1000
+ *
+ * For example, `2` is written as `II` in Roman numeral, just two one's added together. `12` is written
+ * as `XII`, which is simply `X + II`. The number `27` is written as `XXVII`, which is `XX + V + II`.
+ *
+ * Roman numerals are usually written largest to smallest from left to right. However, the numeral for
+ * four is not `IIII`. Instead, the number four is written as `IV`. Because the one is before the five
+ * we subtract it making four. The same principle applies to the number nine, which is written as `IX`.
+ * There are six instances where subtraction is used:
+ *
+ * - `I` can be placed before `V (5)` and `X (10)` to make 4 and 9.
+ * - `X` can be placed before `L (50)` and `C (100)` to make 40 and 90.
+ * - `C` can be placed before `D (500)` and `M (1000)` to make 400 and 900.
+ *
+ * Given an integer, convert it to a roman numeral.
+ */
+
+/**
+ * @param {number} num
+ * @return {string}
+ */
+var intToRoman = function(num) {
+  const map = { M: 1000, CM: 900, D: 500, CD: 400, C: 100, XC: 90, L: 50, XL: 40, X: 10, IX: 9, V: 5, IV: 4, I: 1 };
+
+  return Object.entries(map).reduce((result, [letter, n]) => {
+    result += letter.repeat(Math.floor(num / n));
+    num %= n;
+    return result;
+  }, '');
+};