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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;

/prakash


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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
      ($_,$s)=@_
      Which is one char shorter than
      my$s;$_=pop
      If you also want to keep strictness, you can always sidestep it by replacing $s with a global punctuation variable.

      -Blake

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