gistfile1.pl

use common::sense;

say to_roman(5); #V
say to_roman(18); #XVIII

sub to_roman {
	state $pairs = [
		[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'],
	];

	#add 1 so it's possible to use a single comparison
	my $number = (shift) + 1;
	my $roman;

	#convert negative to positive
	$number *= - 1 if $_[0] < 0;

	for (@$pairs) {
		while ($number > $_->[0]) {
			$roman .= $_->[1];
			$number -= $_->[0];
		}
	}

	return $roman;
}