diff --git a/exercises/practice/roman-numerals/.docs/instructions.md b/exercises/practice/roman-numerals/.docs/instructions.md index 247ea089..50e2f5bf 100644 --- a/exercises/practice/roman-numerals/.docs/instructions.md +++ b/exercises/practice/roman-numerals/.docs/instructions.md @@ -1,41 +1,12 @@ -# Instructions +# Introduction -Write a function to convert from normal numbers to Roman Numerals. +Your task is to convert a number from Arabic numerals to Roman numerals. -The Romans were a clever bunch. -They conquered most of Europe and ruled it for hundreds of years. -They invented concrete and straight roads and even bikinis. -One thing they never discovered though was the number zero. -This made writing and dating extensive histories of their exploits slightly more challenging, but the system of numbers they came up with is still in use today. -For example the BBC uses Roman numerals to date their programs. +For this exercise, we are only concerned about traditional Roman numerals, in which the largest number is MMMCMXCIX (or 3,999). -The Romans wrote numbers using letters - I, V, X, L, C, D, M. -(notice these letters have lots of straight lines and are hence easy to hack into stone tablets). +~~~~exercism/note +There are lots of different ways to convert between Arabic and Roman numerals. +We recommend taking a naive approach first to familiarise yourself with the concept of Roman numerals and then search for more efficient methods. -```text - 1 => I -10 => X - 7 => VII -``` - -The maximum number supported by this notation is 3,999. -(The Romans themselves didn't tend to go any higher) - -Wikipedia says: Modern Roman numerals ... are written by expressing each digit separately starting with the left most digit and skipping any digit with a value of zero. - -To see this in practice, consider the example of 1990. - -In Roman numerals 1990 is MCMXC: - -1000=M -900=CM -90=XC - -2008 is written as MMVIII: - -2000=MM -8=VIII - -Learn more about [Roman numerals on Wikipedia][roman-numerals]. - -[roman-numerals]: https://wiki.imperivm-romanvm.com/wiki/Roman_Numerals +Make sure to check out our Deep Dive video at the end to explore the different approaches you can take! +~~~~ diff --git a/exercises/practice/roman-numerals/.docs/introduction.md b/exercises/practice/roman-numerals/.docs/introduction.md new file mode 100644 index 00000000..6fd942fe --- /dev/null +++ b/exercises/practice/roman-numerals/.docs/introduction.md @@ -0,0 +1,59 @@ +# Description + +Today, most people in the world use Arabic numerals (0–9). +But if you travelled back two thousand years, you'd find that most Europeans were using Roman numerals instead. + +To write a Roman numeral we use the following Latin letters, each of which has a value: + +| M | D | C | L | X | V | I | +| ---- | --- | --- | --- | --- | --- | --- | +| 1000 | 500 | 100 | 50 | 10 | 5 | 1 | + +A Roman numeral is a sequence of these letters, and its value is the sum of the letters' values. +For example, `XVIII` has the value 18 (`10 + 5 + 1 + 1 + 1 = 18`). + +There's one rule that makes things trickier though, and that's that **the same letter cannot be used more than three times in succession**. +That means that we can't express numbers such as 4 with the seemingly natural `IIII`. +Instead, for those numbers, we use a subtraction method between two letters. +So we think of `4` not as `1 + 1 + 1 + 1` but instead as `5 - 1`. +And slightly confusingly to our modern thinking, we write the smaller number first. +This applies only in the following cases: 4 (`IV`), 9 (`IX`), 40 (`XL`), 90 (`XC`), 400 (`CD`) and 900 (`CM`). + +Order matters in Roman numerals! +Letters (and the special compounds above) must be ordered by decreasing value from left to right. + +Here are some examples: + +```text + 105 => CV +---- => -- + 100 => C ++ 5 => V +``` + +```text + 106 => CVI +---- => -- + 100 => C ++ 5 => V ++ 1 => I +``` + +```text + 104 => CIV +---- => --- + 100 => C ++ 4 => IV +``` + +And a final more complex example: + +```text + 1996 => MCMXCVI +----- => ------- + 1000 => M ++ 900 => CM ++ 90 => XC ++ 5 => V ++ 1 => I +``` diff --git a/exercises/practice/roman-numerals/.meta/config.json b/exercises/practice/roman-numerals/.meta/config.json index b14bec8d..80889e9e 100644 --- a/exercises/practice/roman-numerals/.meta/config.json +++ b/exercises/practice/roman-numerals/.meta/config.json @@ -23,7 +23,7 @@ ".meta/example.erl" ] }, - "blurb": "Write a function to convert from normal numbers to Roman Numerals.", + "blurb": "Convert modern Arabic numbers into Roman numerals.", "source": "The Roman Numeral Kata", "source_url": "https://codingdojo.org/kata/RomanNumerals/" }