freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-javascript/691b559495c5cb5a37b9b483.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
691b559495c5cb5a37b9b483	Challenge 123: Roman Numeral Builder	28	challenge-123

--description--

Given an integer, return its equivalent value in Roman numerals.

Roman numerals use these symbols:

Symbol	Value
I	1
V	5
X	10
L	50
C	100
D	500
M	1000

Roman numerals are written from largest to smallest, left to right using the following rules:

• Addition is used when a symbol is followed by one of equal or smaller value. For example, 18 is written as XVIII (10 + 5 + 1 + 1 + 1 = 18).
• Subtraction is used when a smaller symbol appears before a larger one, to represent 4 or 9 in any place value. For example, 19 is written as XIX (10 + (10 - 1)).
• No symbol may be repeated more than three times in a row. Subtraction is used when you would otherwise need to write a symbol more than three times in a row. So the largest number you can write is 3999.

Here's one more example: given 1464, return "MCDLXIV" (1000 + (500 - 100) + 50 + 10 + (5 - 1)).

--hints--

toRoman(18) should return "XVIII".

assert.equal(toRoman(18), "XVIII");

toRoman(19) should return "XIX".

assert.equal(toRoman(19), "XIX");

toRoman(1464) should return "MCDLXIV".

assert.equal(toRoman(1464), "MCDLXIV");

toRoman(2025) should return "MMXXV".

assert.equal(toRoman(2025), "MMXXV");

toRoman(3999) should return "MMMCMXCIX".

assert.equal(toRoman(3999), "MMMCMXCIX");

--seed--

--seed-contents--

function toRoman(num) {
  return num;
}

--solutions--

function toRoman(num) {
  const symbols = [
    ["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 result = "";
  for (const [sym, val] of symbols) {
    while (num >= val) {
      result += sym;
      num -= val;
    }
  }
  return result;
}