Here's one take on the problem: /** * <p>Created by IntelliJ IDEA. * <p>Date: 2/4/21 * <p>Time: 1:36 AM * * @author Miguel Mu\u00f1oz */ public class ToRomans { private static int[] divisors = {1000, 500, 100, 50, 10, 5, 1}; private static char[] romans = {'M', 'D', 'C', 'L', 'X', 'V', 'I'};
/** * Convert a positive, non-zero integer to Roman numerals. * 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. * * Zero cannot be expressed in Roman numerals. The Romans never invented zero. (Yeah. I'm serious.) * @param num The number to convert * @return A string expressing the number in Roman numerals */ public String intToRoman(final int num) { if ((num < 1) || (num > 3999)) { throw new IllegalArgumentException(String.format("Value %d is out of range (1 - 3999)", num)); } int val = num; StringBuilder builder = new StringBuilder(); for (int i = 0; i < divisors.length; i += 2) { int mod = divisors[i]; int v = val / mod; if (v > 0) { if (v == 9) { builder.append(romans[i]); builder.append(romans[i - 2]); } else if (v >= 5) { builder.append(romans[i - 1]); builder.append(repeat(romans[i], v-5)); } else if (v == 4) { builder.append(romans[i]); builder.append(romans[i - 1]); } else { builder.append(repeat(romans[i], v)); } val -= v * divisors[i]; } } return builder.toString(); } private static char[] repeat(char c, int count) { char[] data = new char[count]; Arrays.fill(data, c); return data; } public static void main(String[] args) { int[] testCases = {1, 4, 5, 6, 8, 9, 10, 11, 13, 14, 15, 30, 32, 36, 39, 125, 234, 345, 456, 567, 678, 789, 890, 891, 900, 901, 912, 1234, 2345, 3456, 1567, 2678, 3789, 2001, 2493, 2587, 3888, 3999}; ToRomans s = new ToRomans(); for (int test : testCases) { System.out.printf("%4d = %s%n", test, s.intToRoman(test)); } test(); } private static void test() { Map<Integer, String> dataMap = new HashMap<>(); load(dataMap, 1, "I"); load(dataMap, 4, "IV"); load(dataMap, 5, "V"); load(dataMap, 6, "VI"); load(dataMap, 8, "VIII"); load(dataMap, 9, "IX"); load(dataMap, 10, "X"); load(dataMap, 11, "XI"); load(dataMap, 13, "XIII"); load(dataMap, 14, "XIV"); load(dataMap, 15, "XV"); load(dataMap, 30, "XXX"); load(dataMap, 32, "XXXII"); load(dataMap, 36, "XXXVI"); load(dataMap, 39, "XXXIX"); load(dataMap, 125, "CXXV"); load(dataMap, 234, "CCXXXIV"); load(dataMap, 345, "CCCXLV"); load(dataMap, 456, "CDLVI"); load(dataMap, 567, "DLXVII"); load(dataMap, 678, "DCLXXVIII"); load(dataMap, 789, "DCCLXXXIX"); load(dataMap, 890, "DCCCXC"); load(dataMap, 891, "DCCCXCI"); load(dataMap, 900, "CM"); load(dataMap, 901, "CMI"); load(dataMap, 912, "CMXII"); load(dataMap, 1234, "MCCXXXIV"); load(dataMap, 2345, "MMCCCXLV"); load(dataMap, 3456, "MMMCDLVI"); load(dataMap, 1567, "MDLXVII"); load(dataMap, 2678, "MMDCLXXVIII"); load(dataMap, 3789, "MMMDCCLXXXIX"); load(dataMap, 2001, "MMI"); load(dataMap, 2493, "MMCDXCIII"); load(dataMap, 2587, "MMDLXXXVII"); load(dataMap, 3888, "MMMDCCCLXXXVIII"); load(dataMap, 3999, "MMMCMXCIX"); ToRomans toRomans = new ToRomans(); for (Integer i: dataMap.keySet()) { String expected = dataMap.get(i); String actual = toRomans.intToRoman(i); // assertEquals(String.valueOf(i), expected, actual); if (!expected.equals(actual)) { // in JUnit, replace this block with the line commented out above. throw new AssertionError(String.format("For %d, expected %s, got %s", i, expected, actual)); } } } private static void load(Map<Integer, String> map, int i, String result) { map.put(i, result); } } — Miguel Muñoz ——— 4210 Via Arbolada #226Los Angeles, CA 90042 323-225-7285 – The Sun, with all those planets going around it and dependent on it, can still ripen a vine of grapes like it has nothing else to do in the world. — Galileo On Thursday, May 27, 2021, 03:21:09 PM PDT, Thad Guidry <thadgui...@gmail.com> wrote: Hello, I've checked the source of https://commons.apache.org/proper/commons-numbers but didn't find support for Roman numeral conversion. Is this in another project? Not at all? Planned for Numbers or another subproject like Lang, Text, or Math? Thad https://www.linkedin.com/in/thadguidry/ https://calendly.com/thadguidry/