Re: Re: Luhn Number Golf

[PrakashK]

++. 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

[chipmunk]

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.

[blakem]

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