it-tools/src/tools/roman-numeral-converter/roman-numeral-converter.service.ts

export function arabicToRoman(num: number) {
  if (num < 1) return '';

  const lookup: { [key: string]: number } = { 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 };
  let roman = '';
  for (const i in lookup) {
    while (num >= lookup[i]) {
      roman += i;
      num -= lookup[i];
    }
  }
  return roman;
}

export function romanToArabic(s: string) {
  const map: { [key: string]: number } = { I: 1, V: 5, X: 10, L: 50, C: 100, D: 500, M: 1000 };
  return [...s].reduce((r, c, i, s) => (map[s[i + 1]] > map[c] ? r - map[c] : r + map[c]), 0);
}