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

id, title, challengeType, dashedName

id	title	challengeType	dashedName
691b559495c5cb5a37b9b483	Challenge 123: Roman Numeral Builder	29	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--

to_roman(18) should return "XVIII".

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(to_roman(18), "XVIII")`)
}})

to_roman(19) should return "XIX".

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(to_roman(19), "XIX")`)
}})

to_roman(1464) should return "MCDLXIV".

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(to_roman(1464), "MCDLXIV")`)
}})

to_roman(2025) should return "MMXXV".

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(to_roman(2025), "MMXXV")`)
}})

to_roman(3999) should return "MMMCMXCIX".

({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(to_roman(3999), "MMMCMXCIX")`)
}})

--seed--

--seed-contents--

def to_roman(num):

    return num

--solutions--

def to_roman(num):
    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)
    ]

    result = ""
    for sym, val in symbols:
        while num >= val:
            result += sym
            num -= val
    return result