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);
}