CMC: open-ended-function Write a bijective function which outputs a composite number if given a prime number and a prime number if given a composite number. Bonus points for providing the inverse function

Yes autocorrect, I did in fact mean both objective and bike tire when I typed "bijective" twice

@cairdcoinheringaahing I don't think that's possible

Is there any way to accomplish that besides just implementing "nth prime number" and "nth composite number" and mapping one to the other?

@DLosc except for that

@StackMeter It absolutely is

@DLosc I believe so, but it's a CMC, so anything goes

In fact, yes there's basically infinite different bijective by mapping primes to some infinite subset of the naturals, then mapping that subset to the composites. But that method is likely to be the shortest

Yeah, that's basically what I meant.

CMC: Given a simple regex (only alphanumeric characters and *, +, and ? repetition operators), output all strings that it fully matches.

Related

@DLosc what about [ab]*a

how does one eval that

You don't have to handle character classes for this CMC.

Though you can if you want to. :)

@cairdcoinheringaahing is 1 composite or neither, or can we decide

@DLosc do we have to handle *? and +? non-greedy, or will the input match /([^*+?][*+?]?)*/

@DLosc There are infinitely many if there are any * or +.

@hyper-neutrino Input will match ^([A-Za-z0-9][*+?]?)*$

@hyper-neutrino 1 is neither, and so will never be an input or output

E.g. a+ will match a and aa and aaa etc.

@hyper-neutrino wait what do *, + and ? do

ok, that explains + - one or more

@Adám Correct, which means the challenge is to make sure that any matching string will be output eventually (assuming infinite time/memory/etc).

Oh.

@StackMeter * means 0 or more repetitions, + means 1 or more repetitions, ? means 0 or 1 repetitions

so a*b+c? matches any string with 0 or more a's, then 1 or more b's then 0 or 1 c's

so things like aaaaaaabbbbbbc, bbbbbbbbbbbbbbc, aaaaaaaaaaabc are included

Correct, and also aabb (0 c's).

that is true

I have no idea how you would do this if more than one +/* is involved

that's double infinite recursive

^__^

one does not simply infinitely recurse more than once

you'd need to know in advance the number of pluses

Hint

I think I have an algorithm for it.

@cairdcoinheringaahing yuno, 12 bytes: ιPΞ┥i+1ɨ┝ιP‖ (Try it online!)

@DLosc why? a++ is the same as a+

i will add built-ins to shorten these down but basically it creates an infinite list of primes, finds the index, adds one, and indexes into the infinite list of non-primes (which includes 1, hence the increment)

Basically, start with the shortest string (i.e. set all ? to 0) add a "binary counter" for all repetitions +0/1. Then do the same with +0/1/2, then +0/1/2/3 etc.

@DLosc That somewhat makes sense.

@Adám That works for 2, but what about 3 or higher

> etc.

@hyper-neutrino oh that's the etc.

@StackMeter If you don't want duplicates then remember all you've outputted so far. (inf. memory)

generate all possible strings and filter the ones that match - done :)

Right, that's another one. D'oh.

@ngn how do you know that that will hit every single possible string

@StackMeter C'mon, that's trivial.

i'll be impressed if you manage to generate all strings and not generate all strings

ok I'll give you that one @ngn

Heh, ngn's method doesn't work if the challenge has an arbitrary regex.

@StackMeter well, start with the empty string, then generate all strings of length 1, then 2, etc. - that will go through all of them

@Adám why?

@ngn Because some regexes never terminate.

@ngn Yeah, that's the boring way :)

we're looking for the slick way

@Adám all regular automata terminate on finite inputs

Sure, but today's regexes are not regular.

@Adám the ones from the cmc are

and honestly, I think a Cantor Pairing function would be shorter (it's 6 bytes in Jelly)

> arbitrary

@Adám you said "arbitrary regex". regexes are actually regexes and have always been. pcre-s ("modern regexes") are not regexes.

this should theoretically work but it requires infinite steps to start generating items with an f in it (for the test data I have)

@StackMeter the slick way would be to build an automaton and breadth-first search it

to make the output more interesting I could cartesian product a bunch of infinite sequences together but idk if itertools handles that

> This is the Apocalypse on Pattern Matching, generally having to do with what we call "regular expressions", which are only marginally related to real regular expressions. Nevertheless, the term has grown with the capabilities of our pattern matching engines, so I'm not going to try to fight linguistic necessity here. I will, however, generally call them "regexes" (or "regexen", when I'm in an Anglo-Saxon mood). (source)

@Adám well, exactly

@hyper-neutrino That doesn't theoretically work, precisely because it requires infinite steps before generating some items.

@ngn I deliberately used the term "regex" and not "regular expression" ;-)

@hyper-neutrino I'd be (pleasantly!) surprised if itertools handled cartesian products of infinite sequences

If so, that's the right tool for the job.

@Adám i'm taking that as a joke

@hyper-neutrino if it takes infinite steps to output abcdefgh, I don't think it counts

well idk how that whole infinite automata / turing machine / whatever / the thing WW was talking about a few weeks back theoretically works

is outputting duplicates permitted

actually a simple set() makes it easy to avoid that

yes, if it outputs every possible string in guaranteed finite time

@hyper-neutrino Sure, duplicates are fine.

ungolfed but working, at least i think

@ngn indeed, it's only a fraction of the knapsack problem! :þ

the handbag problem :)

@hyper-neutrino I think that's working, yes!

@pxeger ok what's the knapsack problem

@StackMeter lmgtfy.app/?q=knapsack+problem

@ngn on the other hand, it's always extremely entertaining :)

@pxeger thanks

golfed to 309

just some trivial python golfs

not bad

@DLosc I'd recommend sandboxing that and seeing if it's good for the main site

most would just do ngn's method of iterating through every string, which is boring

@rak1507 subject to the constraints every string possible is generated in finite time

@rak1507 what if we iterate through every string and filter the ones that describe apl flaws? would it be entertaining or boring? :P

@ngn lol

can you make a regex to match apl flaws?

@rak1507 theoretically, maybe

198 with infinite generation

183

@hyper-neutrino what are the asterisks on the ranges

list splat syntax

[*a] = [a[0], a[1], ..., a[-1]]

oh ok

@StackMeter Yeah, what @rak1507 said. :( Plus, if you do it "properly," it's essentially the same challenge as this.

sorry just spent a minute looking through the first 8 pages of the "ok" log and seeing myself on every page multiple times sent my sides into orbit - they'll be coming down in around 2 minutes

@DLosc x nickdrane.com/build-your-own-regex somewhat related

@hyper-neutrino Do the upper have to come first? You can get 174 if not

@Peilonrayz ah, good idea to import string :p forgot about that thanks

order shouldn't matter as long as all get outputted, so this is perfectly fine

you can multiline to make it work

but then users will need to click (see full text) for the link to work

is there a reason why the try it online text is always the same?

is there like something that generates it automatically?

@Yorch What text?

gyazo.com/9272c2b98d25a397473d97818a6bff4e

Try it online!

yeah, Try It Online has formatting options (the link button at the top) and one of those options is SE-submission-style

@Yorch See imgur.com/a/FjIpUzN

you can also use <esc>, <s>, <g> (not a combination)

Oh I hadn't even tried to create the hyperlink yet

no wonder I din't find it

thanks everyone !

@hyper-neutrino Or Github. :P Ungolfed reference solution

works as well :P

my eyes hurt from ungolfed code

@ngn I made sure to use long_explanatory_variable_names just for you ;)

@DLosc this is what Code Review looks like

@ngn please post ngn/k on code review

it would be hilarious

pls no

@rak1507 they gonna eat me alive :)

let's not

that would be sus

@StackMeter Nah, they'd tell me I need better names for my functions, docstrings, put the test code in its own module, etc. :P

oh, it doesn't highlight syntax on math stack exchange :/

@hyper-neutrino I'm so not used to golfing ofc print(*()) wouldn't work with count... We can -1, to 173, by using count. I'm going to go do some 'proper programming' before I join the dark side ;)

@Peilonrayz Hey, Code Review convinced me (reluctantly) to start using snake_case... if Code Golf rubs off on you, I think it's only a fair exchange ;)

@DLosc I've been considering snake_case for a while. What convinced you?

I use pascalCase, because it is objectivelySuperior

don't need to worry about case when all your variables are one letter long

You especially have to worry about case if all your variables are one letter long.

@rak1507 jelly fans: what is a "variable"?

what is a good place to learn about decent casing?

start at a, end at Z, ignore lower/upper

@ngn lol

I just do everything with lower case because I'm a noob

@DLosc I'll let you in on a lil tip. I use all the cases ;) ForClass, FOR_CONSANTS and for_variables.

@Adám It's the Python standard. If I use camelCase, my variable names don't match the naming style of all the standard library functions, which makes the code look inconsistent. (But I still don't like typing underscores.)

part of the reason I like haskell is it lets me pointfree my way out of hard naming decisions :D

[@SandboxPosts RRREEEDDDWWWOOOLLLFFFF!!!!!]

@Peilonrayz Well sure. ;P

@DLosc Ah, visual consistency. Right. The keywords in Dyalog APL are all UpperCamelCase…

@pxeger is this not a dupe of some hamming distance problem?

@Adám Not in QBasic. If you use a in one part of your program and type A by accident somewhere else, the IDE will convert all the previous a's to A's!

@rak1507 no, because the same bit can be flipped twice

oh so it's just n = hamming distance mod 2? or something

e.g. 1100 -> 1101 -> 1100 is distance 2, not just 0 (and any other even-numbered distance)

@DLosc Ah, that's very nice. I had all forgotten that, but what if you load a file that already has a and A?

@rak1507 yes I suppose so

not convinced it's original enough

I didn't really think about that

:(

You have to check is the distance parity is correct and if the distances is smaller than or equal

@Adám I assume it picks one and does the conversion... hold on, let me check.

ooh, on the other hand an APL solution might let me use ≠⌿⍣≡ which would be pretty cool

What bothers me is that thinks like HTMLRenderer and CategoryAXML and JSONToXML are problematic. HTML_renderer and Category_A_XML and JSON_To_XML are much clearer.

@Yorch yes, that. But still not much different than plain hamming distance

@Adám personally I find the first few easier to read

@rak1507 Yes, my eyes stop up at the underscores instead of seeing the name as a whole, but sometimes it can get pretty confusing if there are multiple consecutive abbreviations.

yea that makes sense

HTMLToiPhone

I_think_the_best_option_is_underscores_between_every_word_and_maintaining_capitalisation_consistancy_with_acronyms_like_NASA_and_proper_nouns_like_Rick_Astley

@Adám call it h and put a comment :)

@ngn Problem is that then the spec changes to XHTML, and now you have to change all the hs to xs and it can be rather hard to automate that.

@Adám Yep, it uses the case of the last occurrence.

@DLosc Is it possible to run it before it has a chance to edit (or say the file is read-only)?

@Adám if such a necessity ever arises you can keep it as h and claim it's for backwards compatibility :)

wHAT¯aBOUT¯rEVERSE¯cAMEL¯sNAKE¯cASE?

Unfortunately, Dyalog APL doesn't allow that. Not sure why.

@rak1507 Imagine using variables.

@Adám I'm not sure if there's a way to run code directly without opening it in the IDE. The IDE does the autoformatting as soon as you open the file (though you don't have to save it that way if you don't want to). You can type a one-liner and run it from the Immediate window, which doesn't do any formatting, but you can't open an existing code file there.

This answer is really clever.

@Ausername What answer?

@Ausername you haven't linked to an answer

Finally, in QB64, there's an option to turn autoformatting off (which I use all the time when golfing).

Oops

What do you guys mean?

Of course I linked the answer.

@mods Sorry for the false alarm.

:) I see I got ninja'd

So did I (:

oh hey there art o/

We're rich! (Lot's of diamonds…)

wait, NPSP skipped a post again?

wack. i just tested it in sandbox and they're running so i guess the socket just shut off at an unlucky time i guess. or something like that

¯\_(ツ)_/¯

Maybe the feed wasn't so bad after all. Better late than never, right?

i was worried it'd end up being like this ¯\_(ツ)_/¯ never too late to revert though if we decide we want to

idk if the bot is actually more reliable from my server or if that's just luck - i've run it a minority of the time anyway so it's had less time to fail or die at awkward times

@hyper-neutrino I was wondering where the bot was running, and what the reliability would be.

I think it's currently still redwolf's, and all failures have been on redwolf's server so far, but again maybe not enough sample size

Best to run bots off a data centre…

yeah. I have a proper VPS via monthy subscription; redwolf's is in his basement i think lol

When we ran an APL chat bot ourselves, we ran it off a secure centre at a navy base, right next to the UK-French backbone connection

I keep my vps in a briefcase I always carry with me

oh wait I got confused with a vpn

@Adám i can't tell if you're exaggerating to make a joke or if y'all actually ran a chat bot off a navy base lol

If it's in your basement it probably isn't a vps

just a ps

well yeah. i have a vps where i run my site, redwolf just has a server computer in his basement or smth

@hyper-neutrino Not joking. Gosport, UK.

nice lol

I also have a vps for my site

and I recently learned it has better single thread performance than my computer

although my computer isn't very good

it's just a 3600

I wouldn't mind donating a couple of dollars every so often to help cover costs for the chat bots if we hosted them on a reliable server

I think I already pay about $2 a month for TIO (I should double check that tbh), raising that a bit for server space wouldn't be an issue

I think running the bots on my server should be completely fine and I already would be paying for that either way and I can afford to add NPSP to it with no issues

@hyper-neutrino If you end up running the APL bot, I'm quite sure we'll pay you. (Only reason for not promising anything is that I'm not technically in charge of expenses like that, but considering what we've paid others to do…)

ugh, YouTube is so annoying, I keep accidentally cancelling long comments because focus isn't where I think it is :-(

@Adám I think they still all terminate eventually though

Ah, right, as long as the input is finite, I guess the search (or the universe) much eventually end.

@DLosc that actually makes sense

@DLosc How can I tell if a corpse is safe to eat?

How can I kill adorable animals?

How do I lick a plane?

Arqade is known for weird questions :P