Course of Raku / Addendum 🆕 / Bringing it together / Mixed mini-projects / Exercises / Roman numerals

Solution: Roman numerals

Here is a possible solution to the task.

Code

my @table =
    1000 => 'M', 900 => 'CM', 500 => 'D', 400 => 'CD',
    100  => 'C', 90  => 'XC', 50  => 'L', 40  => 'XL',
    10   => 'X', 9   => 'IX', 5   => 'V', 4   => 'IV',
    1    => 'I';

my $n = 1994;
my $roman = '';

for @table -> $pair {
    while $n >= $pair.key {
        $roman ~= $pair.value;
        $n -= $pair.key;
    }
}

say $roman;

🦋 You can find the source code in the file roman-numerals.raku.

Output

MCMXCIV

Comments

The table lists every symbol in descending value, including the subtractive forms like CM (900) and IV (4), so the algorithm never has to special-case them.
For each entry, the while appends the symbol and subtracts its value as many times as it fits, so the largest pieces are used up first.

← Roman numerals | A reverse-Polish calculator →