Re^2: Determining if a rational number terminates

[tobyink]

in reply to Re: Determining if a rational number terminates
in thread Determining if a rational number terminates

There are probably shorter ways of doing it, but...

# It is important to clearly comment your code to make it easier
# for future maintainers.
#

# This is the numerator, denominator pair for which we wish to
# determine if the decimal expansion terminates.
#
@ARGV = (33, 660);

# Check if it terminates and print "Y" or "N".
#
sub _{@i=sort{$b-$a}@_;return$i[1]if$i[0]==$i[1];@i=($i[1],$i[0]%$i
[1])while$i[1];$i[0]};sub __{$j=_@_;$_/=$j for@_;$_[1]<0and do{$_*=
-1for@_}}__(($k,$l)=@ARGV);$l/=2until$l%2;print$l=~/(5|^1)$/?Y:N,$/

[blackle]

Thanks for that, I didn't even consider that it wouldn't be in lowest form.

It's really clever to take advantage of the fact that powers of five always end with five, I suppose then it's better to divide out the powers of two first than the powers of five. Tomorrow I will ++ both of these :D

[tobyink]

Meh... I was actually only checking multiples of five. D'oh! 1/15 was reporting "Y".

Fixed...

@ARGV = (15, 40);

sub _{@i=sort{$b-$a}@_;return$i[1]if$i[0]==$i[1];@i=($i[1],$i[0]%$i[1
])while$i[1];$i[0]}sub __{$j=_@_;$_/=$j for@_;$_[1]<0and do{$_*=-1for
@_}}__(($k,$l)=@ARGV);for(2,5){$l/=$_ until$l%$_}print$l eq 1?Y:N,$/#

[pemungkah]

+1 for ironic comment on comments.

As we all know, the uncommented part is the part that needs the comment here. (And if you say "the code is obvious and needs no comments", it's my sincere opinion you need to get out more.)

[tobyink]

Actually, if you fix up the whitespace and rename the functions:

• _ => highest_common_factor
• __ => canonical_fraction

... it's not too bad.