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/
