in reply to Re^2: Perl Golf Ethics
in thread Perl Golf Ethics

To do well at Perl golf, perhaps the most important thing is to unearth the "fundamental insights" into the problem. Some of the fundamental insights of this golf were:

Notice that none of these insights depends on knowing Ton's magic formula. Golfers like Ton have a knack for finding these insights quickly and easily, while I struggle; once I find them, it is a simple matter of golfing technique to whittle down the solution. For me, the hard part is to find them. Using the above insights, a simple solution like this:
#!perl -pl map{$_.=(!y/IVXLC/XLCDM/,I,II,III,IV,V,VI,VII,VIII,IX)[$&]while s/\d// +;$$_=$n++}@R=0..3999; y/mp/-+/;s/\w+/${$&}/g;$_=$R[eval]
comes in at around 130. You could get down to around 120, again without knowing Ton's magic formula, by whittling the arabic-to-roman converter:
#!perl -pl map{y/IVXLC/XLCDM//s//$&-9?$&-4?I x$&:IV:IX/e&s/I{5}/V/while/\d/;$$_=$ +n++}@R=0..3999; y/m/-/;s/\w+/+${$&}/g;$_=$R[eval]
To go lower, you'll need to sneak in y/iul-}/-$+ / somewhere to transform $_ directly into symrefs (e.g. $II  +$  III) that can be directly eval'ed. Doing that allows you to eliminate the s/\w+/${$&}/g above. Still further savings are available by replacing the @R array above with a second set of symbolic references, this time mapping negative numbers back to roman numerals.

While I don't fully understand your shortest 186 solution:

#!perl -pla %n=I1V5X10L50C100D500M1000=~/(.)(\d+)/g;sub d{$#_-=$z*2*(@_&&$z<$_)-($z=$_)for@n{/./g};@_}$t+=($.=/p/-/n/||$.)*d for@F;map{$s.=$_ x($t/d),$t%=d}M,CM,D,CD,C,XC,L,XL,X,IX,V,IV,I;$_=$s
it seems like sour grapes to claim that:
this contest was effectively written for a few people who were in the know, who had seen your magic algorithm, shutting out the rest of us.
As shown above, without knowing Ton's magic algorithm, you could have easily trimmed 60 strokes off your solution by unearthing the fundamental insights into the problem.

Update: oops, changed 4e3 to 3999 (4e3 fails test case "MD plus I") plus minor code improvements. Added extra symbolic reference insight.

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