The Nineteenth Byte

orlp

14:00

@LeakyNun yes..?

Kritixi Lithos

A floating point number that is in binary

Leaky Nun

@orlp so the largest prime must be p

orlp

no

Leaky Nun

give me a counterexample

orlp

consider a big prime 2^a+1

New Meta Posts

14:00

0

Q: Should Brain-Flak Birthday challenges be tagged Brain-Flak?

As you may or may not have noticed we are doing a series of Brain-Flak Birthday challenges to celebrate Brain-Flak's first birthday. Some questions in this series are only tangentially related to brain-flak by the balanced-string aspect (and thats fine they're still interesting challenges). The...

orlp

then if we have n = (2^a+1)*11

11 is the biggest prime factor

Nathan Merrill

@KritixiLithos floating point numbers are binary. You could also say they need to print it as a string

Leaky Nun

heh?

orlp

but 11-1 = 10 has a prime factor 2, also found in n

Leaky Nun

I thought (2^a+1) is the biggest prime factor

orlp

14:01

eh

sorry other way around

2^a+1 is the biggest prime factor

but 2^a + 1 - 1 only consists of twos

Leaky Nun

I mean, if n satisfies my condition, then its largest prime factor must be p

orlp

oh I messed up

my bad

my counterexample doesn't work but I'm still not convinced

Nathan Merrill

@KritixiLithos the challenge is basically to use a function that implements this

Leaky Nun

the factorization of n is p^(k-1) (p-1)

the prime factors of n are p and the factors of p-1

Nathan Merrill

or write your own if your language doesn't support floating point

Leaky Nun

14:03

the factors of p-1 must be smaller than p

therefore p must be the largest prime factor

orlp

ah yes, ye

so to see if it's possible

we find the biggest factor of n

then check if n/(p-1) == p^k for some k

Kritixi Lithos

@NathanMerrill Hmmm, I will have a look into that

Leaky Nun

my criterion doesn't work if k=1 for obvious reasons

orlp

@LeakyNun yes it does

k=1 is implicitly excluded

Leaky Nun

I mean my criterion

orlp

14:07

because no number has factorization p^(k-1)(p-1) for k=1

that number doesn't exist

Leaky Nun

e.g. when n=4

orlp

when n = 4 the biggest prime factor is 2

so p^k = 2^2

so k = 2

not 1

remember that k is not undefined, it's simply the multiplicity of p in n

Leaky Nun

e.g. when n=52.

orlp

oh you made a random -1

why didn't you just write n = p^k(p-1)?

Leaky Nun

@orlp heh

because that isn't what my CMC says

orlp

14:10

ah right

no we do need to exclude k = 1

but that makes sense

k = 1 would only occur for prime n

right?

eh I feel I'm confused because we changed notation with +1 -1 like 5 times by now

Leaky Nun

consider e.g. when n=52.

orlp

but either way the algorithm works

2*2*13

so we need to check if 1*12 = 52

and it obviously doesn't

wait, 13 or 1?

(eg. 13^1 or 13^0)

no, 13^1

@LeakyNun sometimes I wish I was a bit more precise..

Leaky Nun

@orlp go on

orlp

@LeakyNun hrm?

I just mean I think kinda fast and loose and informal

Leaky Nun

consider p=53 and k=1

orlp

14:20

>>> def f(n):
...     p, k = max(sympy.factorint(n).items())
...     return n == p**k * (p-1)

Leaky Nun

try f(52).

orlp

false

Leaky Nun

and verify that it should be true by considering p=53 and k=1.

orlp

oh like that

@LeakyNun yeah so if n = p - 1 that's the only exception

I believe

Leaky Nun

yes it is, but how can we deal with that while keeping the code length down?

orlp

14:23

>>> def f(n):
...     p, k = max(sympy.factorint(n).items())
...     return n == p**k * (p-1) or sympy.isprime(n+1)

oh I didn't really care about code length

just an efficient algorithm

Leaky Nun

alright

orlp

although factoring n isn't really efficient

can we do it without factoring n?

@LeakyNun now that I have that function OEIS can help

oeis.org/A114871

_" COMMENTS
These numbers play a crucial role in inverting Euler's totient function."_

haha yes, yes they do

the link is interesting though arxiv.org/abs/math/0404116

Leaky Nun

tio.run/nexus/…

ETHproductions

@HyperNeutrino I just wanted to say, this isn't entirely true: isNaN converts to a number first, so isNaN("a") returns true

Erik the Outgolfer

@ASCII-only I have submitted an issue regarding Charcoal on GH.

orlp

14:40

@LeakyNun ok so we solved part of the problem

now we just need to add 'multiplicative combination' of numbers of the form p**k (p-1)

this would be easy if numbers of the form p-1 didn't exist (aka k = 0)

Leaky Nun

14:55

@orlp how shall we proceed?

@DJMcMayhem challenge: GCD in brain-flak

orlp

@LeakyNun I don't really know

user165474

@ETHproductions Oh, hm. Interesting. I didn't know that. So isNan literally means "is not a number"?

user165474

And I was thinking from a Java perspective :P

betseg

i wrote my java program

was an android app

New Sandboxed Posts

0

A: Sandbox for Proposed Challenges

Give counterexamples to thesis that prime numbers are finite. It is known since antiquity that there are infinite prime numbers, first proved by Euclid. An unorthodox yet brief formulation of this proof was recently posted on MathExchange: There are infinitely many primes, if not, multiply a...

Kritixi Lithos

15:13

@betseg Noice, what did the app do?

orlp

@LeakyNun ok so I have a bit of an idea, not terribly efficient, but an idea

Leaky Nun

fire [insert word]

(what should the world be?)

betseg

@KritixiLithos nothing useful actually

orlp

if we want to know if n is reachable we factorize it and using the factorization get all divisors of n

for each divisor of n we check if d+1 is prime

Kritixi Lithos

Technically, firing up an empty project in Android Studio starts off as a working "Hello, World!" program

orlp

15:20

if yes, then d is reachable

if not then d must be part of the p**k part of p**k(p-1)

Leaky Nun

@orlp what should the word be?

orlp

@LeakyNun I don't understand?

Leaky Nun

there's a phrase "fire x" which would fit that context

but I forgot what the word should be

oh, fire away

orlp

ah

Kritixi Lithos

Yay, my Area 51 proposal has two discussions already (and has 2 followers in total)

ETHproductions

15:27

@HyperNeutrino Yeah, though you have to be careful because e.g. isNaN("1e3") also returns false

It just tells you whether something looks like a non-NaN number or not

orlp

@LeakyNun I think we can greedily assign a big k

consider p**k (p-1)

but we have a number that contains this twice

so p**k (p-1) p**l (p-1)

since (p-1) is reachable by itself we can just split it like this

p**(k+l) (p-1) and (p-1) and we won't reject valid setups

LegionMammal978

Most traumatic April Fools' prank (2018?): give someone a box of donuts with that Nintendo bittering agent applied to them

Leaky Nun

I don't understand this at all. Can you give me an example? @orlp

orlp

well

we looked at the divisors

and found all p-1 that divide n

Leaky Nun

Can you give me a numerical example?

orlp

15:32

eh... no

I'd have to find the right example

but I don't know it

or I could sort of

totient(235) = 184

so 184 is reachable

when we look at all the divisors of 184 we get 2, 4, 8, 23, 46, 92, 184

oh that's a bad example too :(

totient(280) = 96 so 96 is reachable

>>> sympy.divisors(96)
[1, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, 96]
>>> [d for d in _ if sympy.isprime(d+1)]
[1, 2, 4, 6, 12, 16, 96]

oh this is also a bad example because 96+1 is reachable and then you're done :(

@LeakyNun I'm sorry it's really hard to find a nice example without solving the problem itself already

betseg

@KritixiLithos but is it useful

Leaky Nun

@orlp heh, alright

Kritixi Lithos

I don't think a hello world program is useful

Unless for learning

Leaky Nun

I don't understand why every tutorial starts with hello world

is printing to console really that basic and useful?

ArtOfCode

how would you debug if you didn't know how to print to console

Kritixi Lithos

15:40

Your first programs do not need to be that useful

Leaky Nun

@ArtOfCode omg it's you

long time no see

ArtOfCode

I tend to be me, yeah

Kritixi Lithos

Printing to the console gives you an idea on what string are and how they work, as well as boilerplate, if any, and how functions can be called

Leaky Nun

web-beta.archive.org/web/20150117203933/mysmsdiary.co.uk

Apparently this is a thing

betseg

@KritixiLithos for example i dont understand what it means to pass variables by reference or value

i dont understand

ArtOfCode

15:43

@betseg reference = pass the variable by telling the callee where in memory it is

value = give the callee the value and let it put it wherever it wants

I believe

Kritixi Lithos

Is Java by reference or by value?

betseg

oh like *var and var in c

ArtOfCode

yeah

pointer vs value

Kritixi Lithos

well lol, a friend told me that Java was pass-by-reference, but SO says it's by value

Downgoat

@KritixiLithos objects by reference

user165474

15:48

It passes the object by the reference but the variable is by value of the referenced object if that makes sense

Kritixi Lithos

I believe that much of the confusion on this issue has to do with the fact that different people have different definitions of the term "reference". People coming from a C++ background assume that "reference" must mean what it meant in C++, people from a C background assume "reference" must be the same as "pointer" in their language, and so on. Whether it's correct to say that Java passes by reference really depends on what's meant by "reference". — Gravity Jul 30 '11 at 7:23

Leaky Nun

Does anyone care enough to write a Pyth answer for this easy challenge?

Kritixi Lithos

... I never said that

orlp

@LeakyNun ok so

if we get the divisors of n

Riker

@betseg i.imgur.com/INbH0tW.jpg

6

Leaky Nun

15:50

@KritixiLithos sorry

Riker

also:

orlp

and then filter only those divisors that have form p^k(p-1)

then if a subset of those divisors multiply to n, n is reachable

Leaky Nun

@betseg are you interested in Pyth?

betseg

@Riker i cant see them because wikipedia is now banned

Riker

is this when SE is supposed to be down?

betseg

15:52

@LeakyNun dunno

Riker

@betseg wot

betseg

¯\_(ツ)_/¯

Leaky Nun

@betseg would you want to write an answer for the challenge I linked above?

Riker

@betseg you can't see the images?

betseg

imgur is banned too but i can see the images ;)

@LeakyNun meh

Riker

15:53

lol nice

@betseg but wtf why is wikipedia banned

Leaky Nun

@betseg it's not really difficult

betseg

no idea

Riker

that's a ridiculously stupid idea

Fatalize

because dictatorship

Kritixi Lithos

heh, the popularity of Pyth declined rapidly

Leaky Nun

15:54

@KritixiLithos I know, I'm desperate to revive it

user165474

@LeakyNun I'll try that in Jelly (there's probably an answer already; can you tell me if there is?)

Riker

@KritixiLithos when the jelly nation attacked

7

Leaky Nun

@HyperNeutrino yes there is

orlp

@betseg I assume you are in turkey? try to get out if you at all can

betseg

yep ill try

Leaky Nun

15:55

Turkish authorities block Wikipedia without giving reason

Riker

oh, so it's new?

:(

Kritixi Lithos

@Riker The age of stack-based languages is over

Leaky Nun

It's newer than I imagine

@KritixiLithos Pyth isn't stack-based

Kritixi Lithos

Oh, then what is it?

@betseg Do you use a VPN?

Jan Dvorak

Pyth is a compression scheme for Python

betseg

15:58

@KritixiLithos even dns is enough

Kritixi Lithos

so can you view Wikipedia?

Leaky Nun

@JanDvorak would you take up the role to revive Pyth by answering that question using Pyth?

this question

Jan Dvorak

Nope. I'd have to learn it first.

betseg

@KritixiLithos yup

Kritixi Lithos

haha

betseg

16:02

tr.wikipedia.org/wiki/… discussion about the ban :D

Jan Dvorak

tl;dr;translation?

Kritixi Lithos

Google Translate, my friend

Leaky Nun

@JanDvorak I can teach you

Jan Dvorak

(turkish language, didn't read)

betseg

i meant, the discussion is on wikipedia, which is banned

Kritixi Lithos

16:03

How exactly do you use a DNS?

PhiNotPi

@mods unfrizzle room please: chat.stackexchange.com/rooms/38196/phigs

betseg

@KritixiLithos :

$ cat /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4

Leaky Nun

@PhiNotPi link to github?

PhiNotPi

see starboard

Leaky Nun

@PhiNotPi do you get notifications for the form?

@PhiNotPi namesake?

Kritixi Lithos

16:05

@betseg Then what would you do?

betseg

reboot, and if isp isnt forcing its on dns, you use those ips as dsn

Kritixi Lithos

How? For example, how do you use wikipedia?

New Sandboxed Posts

0

A: Sandbox for Proposed Challenges

What would your reputation be without the rep cap? In this challenge, you will calculate what your reputation would be, if there weren't any reputation caps on PPCG. Everyone can access the rawdata for reputation changes on the adress: codegolf.stackexchange.com/reputation. The raw data follows...

PhiNotPi

@LeakyNun no, I mean I can check it when I'm working on stuff

betseg

@KritixiLithos just enter en.wikipedia.org, nothing is needed to use

Leaky Nun

16:09

@PhiNotPi I see

Stewie Griffin

Sorry for all the hassle about the /reputation site. The challenge is ready for review :)

Kritixi Lithos

Then how does a simple cat affect it? (sorry for the stupid questions)

Jan Dvorak

The key is what you cat into

betseg

@KritixiLithos just wanted to show the file

orlp

def is_pk_p1(n):
    p, k = max(sympy.factorint(n).items())
    return n == p**k * (p-1) or sympy.isprime(n+1)

def is_in_totient_image(n):
    if sympy.isprime(n+1): return True
    D = [d for d in sympy.divisors(n) if d != 1]
    e = []
    e = {d for d in D if is_pk_p1(d)}
    generation = e
    while True:
        new_generation = {a * b for a, b in itertools.product(generation, e) if a * b <= n} | generation
        if n in new_generation: return True
        if new_generation == generation: return False

@LeakyNun done

PhiNotPi

16:11

@LeakyNun also I haven't worked on this in a long time so I don't really remember what state everything is in. I might rewrite most stuff.

Leaky Nun

@PhiNotPi alright

DJMcMayhem

@LeakyNun ugh, that sounds hard

Leaky Nun

@DJMcMayhem I agree

Kritixi Lithos

@betseg So how do you use that file?

Or do you not use it at all?

Leaky Nun

@orlp nice

orlp

16:14

so we know for example that 1235982240 is indeed an output of the totient function

betseg

@KritixiLithos nameserver IP

in that file

Kritixi Lithos

what do you do with the IP then? (I don't really know much on how DNS works)

New Main Posts

0

Q: Sort digits by their first occurence in PI

Task Given a non-negative number n sort n's digits by their first occurence in PI. Rules Submit a program or function that does the above task. Input can be taken via function or cli argument or STDIN. Output via return value exit status or STDOUT.

code-golf number sorting pi

Kritixi Lithos

@Downgoat Thanks for following :) How much of an enthusiast are you?

Downgoat

Sorry but following what?>_<

betseg

16:20

@KritixiLithos that it is the DNS's ip, you enter whatever IP you want (i use Google DNS, so i have 8.8.8.8 and 8.8.4.4)

Kritixi Lithos

@Downgoat Prehistoric Animals

# This file is not used by the host name and address resolution
# or the DNS query routing mechanisms used by most processes on
# this Mac OS X system.

That must be why it doesn't work

betseg

lol

twitter.com/BTKbasin/status/858356056229130240 they say wikipedia say turkey supports terrorists

PhiNotPi

Basically, the thing that's weird about Phigs, is its absolutely convoluted control flow.

It's like a stack-based and non-stack-based language merged together.

Downgoat

16:38

@KritixiLithos oh. I'm not a paleontologist or anything, mostly just interested in evolution and all

Kritixi Lithos

I'm not a palaeontologist either, just interested in dinosaurs and other creatures, and slightly less interested in evolution (if mammal-like reptiles evolved into mammals, then is it possible for mammals to evolve back into reptiles?)

Downgoat

@KritixiLithos I given at the current rate of environment change I'd say no

Kritixi Lithos

Or we'd just extincitify that species before it even has a chance

sad reality of life

PhiNotPi

16:57

@KritixiLithos back into "reptiles" won't/can't happen, but there's nothing really stopping some mammals from evolving into things moderately similar to reptiles.

Like how whales are mammals that were originally on land but went back to live in the water, etc.

Kritixi Lithos

5 upvotes in 1 minute, wow

ETHproductions

on what?

Kritixi Lithos

This one: codegolf.stackexchange.com/q/118107/41805

ETHproductions

WHAT

That's on-topic here now? I thought it wasn't

Geobits

I'm struggling to decide if that's even on topic, but leaning toward no.

ETHproductions

17:09

I believe this is ready for re-opening

PhiNotPi

I think stuff like that has been asked before and been shut down.

Geobits

I think so too

I think there's something on meta asking if it's on topic, but can't find it right now (mobile).

ETHproductions

13

Q: An improved version of GolfScript

I am planning to write an improved GolfScript for even shorter programs that can do more things. This is not a challenge; it is a request for feedback and tips on what I should do. (see tags) I'm not sure if this should be Community Wiki. If you think so, just flag for a moderator to convert it ...

code-golf tips golfscript

Phoenix

Woot! 2K rep!

ETHproductions

^^ Very similar, closed as too broad

Phoenix

17:12

I can finally see deleted posts!

> As one of our most experienced users, ...

Whatever you say, site.

Geobits

I wonder if it would be more on topic at software engineering? I'm not sure if it fits their scope, to be honest.

Phoenix

Well, the area 51 proposal for Language Design got closed as a dupe of an existing site.

And I'm reasonably certain it's software engineering

ETHproductions

@Geobits I'm 99% sure it's not in their scope. I mean, how many of their common users would have had more than trivial experience with golfing languages? :P

Kritixi Lithos

It got closed now

ETHproductions

I do think "tips for designing feature X in golfing languages" would be on-topic though

New Main Posts

17:19

8

Q: Tips for making a golfing language

I am currently working on a golfing language. Do you have any suggestions for it? What in your language of choice is helpful for golfing? What feature do you wish you had? Do you suggest variables, stack(s), tapes, registers, etc? As usual, please post separate tips in separate answers.

code-golf tips language-design

Kritixi Lithos

That's what the comment also states ^^

Geobits

@ETHproductions Maybe not golfing languages in particular, but language design maybe.

ETHproductions

True.

Geobits

Yeah. Maybe something more like what was asked in chat recently "Should stack based languages take string input in normal or reversed order?" or something.

Kritixi Lithos

@Geobits That might be much broader. Different languages are written with different goals/intentions.

Geobits

17:21

Sure, it's still really broad.

I think asking a specific question about a language feature might be fine on either site.

Kritixi Lithos

Another question related with ^^^^ "Should each numerical digit in 2D stack-based languages push a separate number?"

Geobits

They're both still kinda poll-ish, but at least you can lay out your arguments and give examples in the answers.

Of course the answer to either is probably "it depends" :P

ETHproductions

I'd say make it less of a yes/no question by asking "How would multi-digit numbers work best in 2D stack-based languages?" or similar

Geobits

Yeah. I could see a good answer giving a few options with examples, and explaining the pros/cons to each method.

Leaky Nun

I'm still looking for a Pyth answer to this challenge. I really don't want to do it myself. It's just a few commands.

Geobits

17:25

Some of our users would probably be very good at writing something like that up.

Kritixi Lithos

I think a community-wiki would be best

Then other users can add other options that they think would be necessary

Geobits

I'm not sure CW is the right way to do that.

ETHproductions

Why not have each option in a separate answer?

You could still explain the pros/cons of each, and then they could be voted on individually.

Kritixi Lithos

Yeah, similar to a Tips for golfing in X question

Geobits

Well, it may be easier to compare/contrast things in a single "essay" format written by one person. That's not to stop anyone else from offering their opinions, obviously.

There's no reason at all to limit it to one answer

And voting for the post rather than the individual options makes it less of a poll anyway.

Kritixi Lithos

17:28

Ooh

@MartinEnder If tips for golfing in <all langauges> on-topic than why isn't this? — programmer5000 4 mins ago

Geobits

Heh. I don't agree that it is, tbh.

Leaky Nun

I hope I don't need to use a bounty to get people answer that challenge in Pyth... It's not really hard.

Geobits

But it actually might be narrower, since answers should pertain to the majority of languages, it leaves out all language-specific things, which are the majority of tips.

New Main Posts

17:52

2

Q: Tips for storage in a golfing language

I am writing a golfing language. Do you suggest variables, stack(s), tapes, registers, etc for storage in a code-golf language? What about implicit imput?

code-golf tips language-design

Kritixi Lithos

18:02

@EriktheOutgolfer The PPCG userscript doesn't recognise your Pyth answer as the shortest answer for some reason

orlp

@LeakyNun fq1iTQUQ

Leaky Nun

@orlp you posted?

orlp

the last Q can be ommited

no

Leaky Nun

why not?

Erik the Outgolfer

@KritixiLithos It does, but it will not when the 05AB1E answer applies Adnan's golfing tip.

Leaky Nun

18:06

@KritixiLithos you may need to refresh

@Adnan the outgolfer is here

Kritixi Lithos

haha

Erik the Outgolfer

Huh?

Adnan

hahaha

Erik the Outgolfer

It just sounded like "Adnan the ~~Outgolfed~~ Outgolfer" is here lol. (interesting typo)

Leaky Nun

@EriktheOutgolfer that was intentional

because he is the outgolfer

Erik the Outgolfer

18:08

No it wasn't I really typed "Outgolfed" by mistake but I just striked over since it was a bit... interesting.

@LeakyNun I have outgolfed him in the past though.

Leaky Nun

@EriktheOutgolfer focus on the present

Erik the Outgolfer

Yeah, even though my name is "the Outgolfer" I rarely outgolf... rarely anyone outgolfs either, except if their name is "Dennis".

Leaky Nun

heh

Erik the Outgolfer

And they have a currently-1-year-old-diamond next to it.

Leaky Nun

@EriktheOutgolfer I swear I just need one breakthrough.

@EriktheOutgolfed

Kritixi Lithos

18:17

That pinged him

Leaky Nun

@KritixiLithos I used U+200B

Kritixi Lithos

But you used a d instead of an r

Leaky Nun

@KritixiLithos I used U+200B which treats everything after it as not a part of the ping

Erik[U+200B]theOutgolfed

is equivalent to Erik theOutgolfed

Kritixi Lithos

ah, I see

Leaky Nun

and only 3 initial matching letters are required

ETHproductions

18:21

@LeaningTowerofPisa

8

haha, that's cool

Leaky Nun

you win

Adnan

hahahhaha

Leaky Nun

-,- not funny

Wheat Wizard

Has anyone here programmed in Parenthesis hell?

ETHproductions

dl.dropboxusercontent.com/u/15495351/cjam.pdf Nooooo, all my knowledge of CJam is gone :-(

Kritixi Lithos

18:30

I noticed that something like a month ago when I decided to use CJam for a challenge. Gave up instantly

Leaky Nun

@ETHproductions no it isn't

@KritixiLithos no you don't have to

ETHproductions

@LeakyNun Aw, sweet, I forgot about archive.org :-)

Quick poll: What are tape-based golfing languages (like BF, but way golfier) good at compared to e.g. stack-based langs? (if anything...)

Rather, what operations that come up sometimes in code golf would be easier on a tape than on a stack?

Kritixi Lithos

I don't really understand the difference

noɥʇʎԀʎzɐɹƆ

Nathan Merrill

A trivial one: Implement a tape

but realistically speaking, any task that requires a deque is far easier on a tape

mınxomaτ

18:36

@NathanMerrill 📼

ETHproductions

@KritixiLithos On a tape, values are fixed in place, so if you have e.g. [1,2,3] you can move to the 2 and change it to 0 (so you have [1,0,3]), where as in a stack-based language you could just delete the second item and end up with [1,3]

Kritixi Lithos

Oh, now I understand the comparison with BF

ETHproductions

I suppose tapes are fairly good at anything that requires taking data from arbitrary indices in the middle of the array

I'd like to see a tape-based golfing language

Stewie Griffin

Comments?

Adnan

18:52

@noɥʇʎԀʎzɐɹƆ out of scope?

Leaky Nun

Does anyone here use strawberrynet.com ?

Just a reminder not to use it, because it has great security issues...

ArtOfCode

as in it leaks your full name and address if an attacker has your email

Leaky Nun

^

@orlp you can do it in 5 bytes...

Never mind, I'll post it anyway

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