I was just looking at the about.com Perl site, and it has this article about finding if a number is a valid Luhn number, which, apparently, tells you it's a valid credit card number.
If what you've got is divisible by ten, it's a valid credit card number.
Their solution is at http://perl.about.com/library/weekly/aa080600h.htm, and of course it's quite long, because it's a teaching exercise.
I got thinking about it and how to do it more compactly, in the spirit of "Regular Expressions -- is there anything they can't do?" and tried to make it as short as I could.
Here's an attempt, but I'd love to see you make it shorter:
- double the value of every other digit, counting backward from the second-last
- add all the digits of the resulting numbers together (not the numbers, but the digits of the numbers, so if you've got 16, you add it as one plus six)
- add the leftover numbers together
- add them to the sum of the other lot of numbers
If what you've got is divisible by ten, it's a valid credit card number.
Their solution is at http://perl.about.com/library/weekly/aa080600h.htm, and of course it's quite long, because it's a teaching exercise.
I got thinking about it and how to do it more compactly, in the spirit of "Regular Expressions -- is there anything they can't do?" and tried to make it as short as I could.
Here's an attempt, but I'd love to see you make it shorter:
$n = '4564123800603607'; # this is not my credit card number ($o = reverse($n)) =~ s/.(.)/($1*2)/ge; # every other number in it, times 2 # (reversed because then it will work # for numbers of different lengths, as # some cards are 13, not 16). ($e = reverse($n)) =~ s/(.)./$1/ge; # the other numbers, not times 2 $o =~ s/(.)/$x+=$1/ge; $e =~ s/(.)/$y+=$1/ge; # add the digits printf("%sValid.",(($x+$y)%10 == 0?'':'Not ')); # print the result
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Replies are listed 'Best First'. | |
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Re: Luhn Number Golf
by japhy (Canon) on Feb 26, 2002 at 13:57 UTC | |
Re: Luhn Number Golf
by jmcnamara (Monsignor) on Feb 26, 2002 at 15:27 UTC | |
Re: Luhn Number Golf
by demerphq (Chancellor) on Feb 26, 2002 at 15:24 UTC | |
Re: Luhn Number Golf
by chipmunk (Parson) on Feb 26, 2002 at 19:57 UTC | |
by PrakashK (Pilgrim) on Feb 26, 2002 at 21:47 UTC | |
by chipmunk (Parson) on Feb 26, 2002 at 22:15 UTC | |
by blakem (Monsignor) on Mar 08, 2002 at 09:10 UTC | |
by petral (Curate) on Feb 27, 2002 at 17:02 UTC | |
Re: Luhn Number Golf
by PrakashK (Pilgrim) on Feb 26, 2002 at 17:45 UTC | |
122 Char Sub - Re: Luhn Number Golf
by metadoktor (Hermit) on Feb 26, 2002 at 13:29 UTC |
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