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Re: Re: Luhn Number Golf

by PrakashK (Pilgrim)
on Feb 26, 2002 at 21:47 UTC ( #147740=note: print w/replies, xml ) Need Help??

in reply to Re: Luhn Number Golf
in thread Luhn Number Golf

++. 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;


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Re: Re: Re: Luhn Number Golf
by chipmunk (Parson) on Feb 26, 2002 at 22:15 UTC
    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.


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