Converting Integers to Roman Numerals - Java

Converting integers to their roman numeral equivalents

To minimize confusion, I suggest making two function instead of one:

private static final String[] ROMAN_LETTERS = {"I", "IV", "V", "IX", "X", "XL", "L", "XC", "C", "CD", "D", "CM",  "M" };
private static final int[] ROMAN_NUMBERS    = {  1,    4,   5,    9,  10,   40,  50,   90, 100,  400, 500,  900, 1000 };

public static String romanizer(int num) {
    StringBuilder result = new StringBuilder();
    for (int h = ROMAN_NUMBERS.length - 1; h >= 0; h--) {
        result.append(ROMAN_LETTERS[h].repeat(num / ROMAN_NUMBERS[h]));
        num = num % ROMAN_NUMBERS[h];
    }
    return result.toString();
}

public static List<String> romanizer(List<Integer> numbers) {
    List<String> result = new ArrayList<>();
    for (int num : numbers)
        result.add(romanizer(num));
    return result;
}

Converting integers into words and roman numerals

Take a look at cl-format, it can return "twenty one", I used that for project euler.

http://clojuredocs.org/clojure_core/1.2.0/clojure.pprint/cl-format

and Roman too:

~@R prints arg as a Roman numeral: IV; and ~:@R prints arg as an old Roman numeral: IIII.

Sorting roman numeral in java

You can use the Comparator util class to compare by the actual numeral value:

static void sortRomanNumerals(List<String> romanNumerals){
    romanNumerals.sort(Comparator.comparing(Main::romanToDecimal));
}

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