roman.pl

use v5.16;
use warnings;
use Test::More tests => 13;

sub to_roman {
    my ($num) = @_;
    my $out = '';

    my @mapping = (
        [ 10000 => 'Q' ],
        [ 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' ],
    );

    while ( $num > 0 ) {
        for (@mapping) {
            my ( $decimal, $roman ) = @$_;
            if ( $num >= $decimal ) {
                $out .= $roman x ( $num / $decimal );
                $num = $num % $decimal;
            }
        }
    }

    return $out;
}

is to_roman(1), "I";
is to_roman(2), "II";
is to_roman(3), "III";
is to_roman(4), "IV";
is to_roman(5), "V";
is to_roman(6), "VI";
is to_roman(7), "VII";
is to_roman(8), "VIII";
is to_roman(9), "IX";
is to_roman(10), "X";

# Wikipedia examples
is to_roman(1954), "MCMLIV";
is to_roman(1990), "MCMXC";
is to_roman(2008), "MMVIII";