I rarely define such subroutines without also defining the inverse. And once you have the inverse it seems like the most natural thing to do is use it to set up a straight forward table-driven version of the required routine:
#! perl -sw
use 5.010;
use strict;
use constant _1to9 => [ '', qw[ I II III IV V VI VII VIII IX ] ]
+;
use constant _10to90 => [ '', qw[ X XX XXX XL L LX LXX LXXX XC ] ]
+;
use constant _100to900 => [ '', qw[ C CC CCC CD D DC DCC DCCC CM ] ]
+;
sub dec2roman {
my $dec = shift;
die "Bad input' unless $dec =~ m[^[0-9]+$] and $dec < 4e3;
my @decDigits = split '', $dec;
my $roman = '';
$roman .= 'M' x shift @decDigits if @decDigits == 4;
$roman .= _100to900->[ shift @decDigits ] if @decDigits == 3;
$roman .= _10to90-> [ shift @decDigits ] if @decDigits == 2;
$roman .= _1to9-> [ shift @decDigits ] if @decDigits == 1;
return $roman;
}
sub roman2dec {
state %roman2dec;
%roman2dec = map{ dec2roman( $_ ), $_ } 1 .. 3999 unless %roman2de
+c;
my $roman = uc shift;
return $roman2dec{ $roman } if exists $roman2dec{ $roman };
die "Input '$roman' out of range (1..3999 (roman) inclusive)";
}
for my $r ( qw[ XLII LXIX mi MMMCMLXXXVIII ] ) {
printf "%15s : %d\n", $r, roman2dec($r);
}
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
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