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Re: Luhn Number Golf

by chipmunk (Parson)
on Feb 26, 2002 at 19:57 UTC ( #147694=note: print w/replies, xml ) Need Help??

in reply to Luhn Number Golf

This is 60 characters. I've verified it by comparing the results to the referenced code from
sub luhn { # 1 2 3 4 5 6 #23456789012345678901234567890123456789012345678901234567890 my$s;$_=reverse@_;s/(.)(.)/$1.$2*2/ge;$s+=$_ for/./g;!chop$s }

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Re: Re: Luhn Number Golf
by PrakashK (Pilgrim) on Feb 26, 2002 at 21:47 UTC
    ++. You can eliminate reverse and shorten it to 55.
    sub luhn { # 1 2 3 4 5 #234567890123456789012345678901234567890123456789012345 my$s;$_=pop;~s/(.)(.)/$2.$1*2/ge;$s+=$_ for/./g;!chop$s }
    and, if you don't care for strict-ness, shave another 5 chars, by eliminating my$s;


      Unfortunately, you can't simply eliminate reverse. Cody Pendant explained why in the comments in his solution; if the number has an odd number of digits, you'll end doubling the wrong digits. For example, your solution would return true for 548979844, which is not a Luhn number.

      You shouldn't eliminate my$s; either. That's not there for strict-ness, but to allow the subroutine to be called more than once. Without it, $s would keep its values between calls, throwing off all the subsequent answers.

        If you aren't going for strictness, you can get the same initialization effect with
        Which is one char shorter than
        If you also want to keep strictness, you can always sidestep it by replacing $s with a global punctuation variable.


Re: Re: Luhn Number Golf
by petral (Curate) on Feb 27, 2002 at 17:02 UTC
    52 chars:
    sub luhn { $_=reverse@_;s/(.)(.)/$1.$2*2/ge;s/\B/+/g;eval=~/0$/ }


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