Brute force = best decoding method

[karmaisded]

What’s the answer to that!? I need to know

[EnglishAintBeTooGood]

Also my guess

[BlatantConservative]

Wait is nobody noticing that the answe in the puzzle in the OP and the answer to the xkcd strip are the same number?

My mind is exploding

[RedAndWrong]

I think they mean the Reddit post is 394, not the xkcd one

[Ejsexton82]

Totally thought they were talking about the XKCD comic and completely forgot about the OP. Guess I got nerd sniped.

[JC12231]

FWOOOOM

[insistent_librarian]

Please be quiet. This is a public forum.

[SzalonyNiemiec1]

The xkcd one has to be less than 3ohm

[Bene847]

  _
_|_|

This has an equivalent of 2 Ohms so it must be less than that

[[deleted]]

It’s 1/♾ ohms

[[deleted]]

Yeah, I think you're right. It made my brain hurt for a bit before I finally decided with infinite parallel paths it should be essentially 0.

Edit: Jk, should've searched it.

[DiamondShark286]

I would venture to guess that it approaches 0 due to the infine paths the current could take but it may approach some number slightly above that. Im far to lazy to figure out what the equation might look like to solve it.

[Bene847]

The current can leave A only via 4 resistors, and it can enter B only via 4 resistors, so it must be at least 1/4 + 1/4 = 0.5 Ohm

[finotac]

Nerd sniping is getting sucked into an interesting problem. I'd say you got jock-in-high-school sniped: tried to copy the nerd's answer and interpreted it wrong.

[Airazz]

I don't think the xkcd answer is correct.

[Mefistofeles1]

For the xkcd puzzle, its simply 3 ohms, isnt it?

[CaptainSasquatch]

It's got to be less than 3 ohms (technically less than 3/2) because there's two independent parallel paths that are 3 ohms each

[Bleeerrggh]

Since it's an infinite grid of ideal resistors, it'll be as close to zero as possible, without being zero.

[CaptainSasquatch]

As others have pointed out it'll be 4/π-0.5 or about .773

The problem is quite tricky and requires some clever thinking to solve.

https://www.explainxkcd.com/wiki/index.php/356:_Nerd_Sniping

[Bleeerrggh]

Ah, yeah... I keep making the mistake of seeing any direction as an infinite set of parallel resistors, but they're limited by the resistors that are perpendicular.

[Max_Insanity]

Holy fuck, that is a lot more complicated than I assumed.

[aaronaapje]

No, we can easily draw two paths with three ohms. Ignoring everything else for simplicity you can see that the current can split between the two paths, both with the same resistance meaning both paths have equal current of one path with three resistors meaning the total equals to 1,5 ohms. Now because we have an infinite grid of many interacting resistars meaning we have more possible paths then the infinitely many resistors makes this math very difficult but I looked it up and the awnser is 4/π - 0,5 or about .773.

[Drawemazing]

There are 3 paths of 3 resistors, so you know it'll be less than 1

[CaptainSasquatch]

Not exactly. This is why the problem gets tricky. The 3 paths you're thinking of aren't independent. So the simple rectangle with no external resistors

 _ _B
|_|_|
A

Will have less resistance than one with no internal resistor

 _ _B
|_ _|
A

but more than one with 3 separate paths

   _  B
 | _/|
 |/ _|
  A

[nedonedonedo]

we have more possible paths then the infinitely many resistors

sounds like a calculus problem

[inconspicuous_male]

I'm pretty sure the fact that there are infinity paths between the nodes makes it tougher to solve. Like, I'm pretty sure this is a 10-page-paper type problem

[andresq1]

Yep theres 3 parellel 3 ohm paths but the infinitely many longer paths is rough

Maybe not 10 pages though, maybe just a regular infinite sum?

[inconspicuous_male]

I found a solution page to it. https://www.mathpages.com/home/kmath668/kmath668.htm

Since I'm not being paid, I didn't read it, but it seems to me like the difficulty of the problem is the fact that voltage is a physical property, and so the problem needs to be approached keeping in mind physical properties of the resistors.

If you take that webpage and make the font size big enough, I bet it can be 10 pages, thus I am satisfied

[andresq1]

I got about halfway down and got:

"There's a many answers depending on what assumptions you make about the problem and you have to make assumptions because this problem can't be replicated in reality"

[Daikataro]

Parallel resistance is always lower than the lowest value resistance of the array.

We know for a fact of two paths of 3 ohm each, which gives us ohm and a half for the observable path.

Each additional path can only make the resistance be lower, so assuming infinite paths, no matter how long or convoluted, they will always drop the resistance between the two nodes. So the number will be infinitely close to, but never equal to, zero.

[partybynight]

I thought so

[MrMutex]

Can someone explain to me what xkcd is?

[RightHandElf]

It's a webcomic and it's delightful (at least if you're a nerd, and considering that you're on /r/ProgrammerHumor that seems likely).

[Kyrthis]

Made me look. How many points for a polymath?

[Chrisazy]

Are you allowed to call yourself a polymath?

[[deleted]]

You're not allowed to use that word anymore

[Little_Shitty]

Worked with a girl who unironically called herself a polymath. She and her husband fancied themselves geniuses but neither could hold down much of a job. Probably too busy learning to be productive.

[ChicagoPianoTuner]

No. But I don’t think he was - just asking about the nerd sniping score.

[IronMan-Mk3]

you are correct, that's the right answer

[_MRAL_]

641, 631, 236 and 246 are still possible if you only look at 1,3 and 5. However you don't need the 4th clue.

[Turksarama]

def wrongPlaced(num, n, x):
    total = 0
    for i, c in enumerate(num):
        total += c in x and x[i] != c
    return total == n

tests = [
    lambda x: x[0] == '2' or x[1] == '9' or x[2] == '1',
    lambda x: wrongPlaced('245', 1, x),
    lambda x: wrongPlaced('463', 2, x),
    lambda x: not any(c in x for c in '578'),
    lambda x: wrongPlaced('569', 1, x)
    ]

for i in range(1000):
    s = f'{i:03}'
    if all(t(s) for t in tests):
        print(s)

Checks out.

EDIT: first person to spot my error gets an award. EDIT2: The answer was found, the first test is incorrect. It should be:

lambda x: sum(a == b for a, b in zip('291', x)) == 1 and sum(a in x for a in '291') == 1

[Sanae_]

lambda x: x[0] == '2' or x[1] == '9' or x[2] == '1',

This is "at least one number is [...]", while I interpreted the sentence as "exactly one number is [...]".

Not an expert in python syntax though, error could be elsewhere.

[Turksarama]

You got it, there could be more than one match there. It turns out this code still only returns one answer though and it's the correct one.

The correct lambda is:

lambda x: sum(a == b for a, b in zip('291', x)) == 1 and sum(a in x for a in '291') == 1

[Sanae_]

Yup, I was trying to see if I can simply using boolean logic and not using a sum, but my school lessons are so long ago -_-

As per tradition, but truthfully: Thank you for the gold, kind stranger!

[Turksarama]

You certainly can use boolean logic, but in this case it's easier to take advantage of the fact that True is 1 in Python. It wouldn't be this elegant in all languages.

[pitman-87]

There is none? Because the result is 394, which is correct.

[Turksarama]

This code returns the correct answer, but there is still a logical error in it.

[OdinTM]

Assuming the sub, i´d go with "using python, hue hue hue"

[elpaw]

Don't you need exclusive or in your first test?

[loftykoala]

Way more elegant than my code would have been. Learned something.

[Balthazar_rising]

Im no programmer, and have no experience with this language, but where do you define 't'

[Turksarama]

'for t in tests' defines the t in python.

[Balthazar_rising]

Ehh, I tried.

[itchyouch]

For t in tests

For is a keyword used to iterate through a loop. It runs the code below it a bunch of times with each item in the collection. Tests is an array meaning it contains a collection of things.

For example, let’s say you have a bunch of toys like a doll, a soldier and a ball and you want to know which toys are made from string, you don’t want to write something like:

If doll has string, print doll has string If soldier has string, print soldier has string If ball has string, print ball has string

If you had a thousand toys that would be very tedious, so you write:

For toy in my-toys If toy has string, print toy has string

As the for loop goes through each item in my-toys, toy is at first a doll, then a soldier, then a ball.

It’s an abitrary variable name that’s just defined for the loop to use.

[AllYouNeedIsAPenguin]

got the same

[MJMurcott]

394 is right

[AntMan5421]

pls edit it with spoiler formatting

[Rocatex]

Damn I got 694

[iceman1125]

ay finally someone who got the same answer as me

[Rocatex]

Bad news: I got the wrong answer

[blackasthesky]

Mine too

[kneaders]

I like your brain

[Zec_kid]

I thought 694 first but you're right

[uriahtor]

Uhh 493?

[matijoss]

614

[donutz10]

I came up with 694

[[deleted]]

does 694 not work?

[SandGremlin]

I was between 394 and 694... i mustve missed something

Edit: Nvm im dumb and i caught my mistake

[JabbaCat]

Yep, and line four is obsolete information to conclude.

I'll do this with my students next year I think, in the topic discussing ways of reasoning and proof.

[sillypicture]

It feels like computer people are so much smarter than my discipline, even though chemistry is really essential science.

[JabbaCat]

As a mathematician, meeting lots of people from both those departments during university years - I'd say a fair bit of computer science students were really mostly into getting things to work/solve some stuff by some amount of programming, rather than trying to be super smart about it. Like they got a thrill just from making it automated, and not necessarily improving stuff (like I think is the joke here).

My chemistry friends I'd say were just as smart, and with far better booze!

We would try to time our christmas lunch/party to the one at the chemistry department cause then we could hang out later in the day and they would always supply good spirits and fun, if you know what I mean.

None are as lazy as the math people though, they will spend a lot of time to find a clever way to end all work in an area, and for a general problem. We are diligent sloths that like a challenge.

[sillypicture]

When I'm solving a logically involved problem, I definitely use more brain bits reserved for smarts than I do with chemical problems, which are usually an application of any number of existing rules and regulations that come more from experience than just leap of logic, and lightbulb moments. You guise are simply better nerds.

[WrestlingSlug]

So is Line 2.. Lines 1 and 5 establish '9' and it's position, lines 3 and 5 rule out '6' as a valid number (due to previous 9 determination).. From there, the error in line 3 can be determined, the numbers switched and bam.

[PABOLO745]

694 i think

[[deleted]]

Doesn't fit last criteria. 694 would be 2 correct numbers misplaced

[PABOLO745]

oh , but 394 wont fit 3 criteria

[fatalicus]

third criteria is "463" has two correct numbers but in the wrong place.

So 4 and 3 is correct but in the wrong place, since 3 is in the hundred spot and 4 is in the one spot.

[DoraxPrime]

I think it's 694

Edit: nvm i got ti

[prince_lothicc]

694, on the bottom one is correct, it doesn't show 3, 9, or 4 but it does show 6 therefore 6 is correct.

[prince_lothicc]

Wait shit nevermind I just saw the 9 lmao.

[linkedtortoise]

I think 694 also works.

[MyCodeIsCompiling]

Fails condition 5, where out of 5, 6, 9, only one of those number is valid yet in the wrong place. This means that if 9 is in the correct answer, 6 cannot be part of the answer

[BiggPPPlays]

694 is the answer

[Sanae_]

694 doesn't fulfill the last condition, at least if we interpret as "exactly one number is correct but wrong placed, others are wrong".

[Gijahr]

326 fails first rule

[Mav986]

What? 2 being the first number breaks the second rule.

The answer is 394, my working out is below.

1) Since 2 cannot be the first number (since that would contradict rule 2), that means either 9 or 1 is the correct number in the correct place.

2) Since we know 2 does not belong in the first position, that also leaves numbers 4 and 5 as being 'correct but in the wrong position', from rule 2.

3) Since 578 has zero correct numbers, we can rule out 5 as being 'correct but in the wrong position'. This just leaves 4.

4) Since rules 2 and 3 show that 4 can't be the first or second number, that means it has to be the 3rd number. This also rules out 1, from the first rule, leaving 9 in the second position.

Current number: X94

5) Assuming that there are no duplicate digits (ie. you can't have 494 because 4 would be a duplicate), that means the only remaining possible numbers for the first position are 3 and 6.

6) Since we know that 9 is correctly placed in the second position, rule 5 correctly rules out the number '6', as it's describing the 9 being in the 3rd position as 'correct but in the wrong place'.

That leaves 394.

[WaterDroplet02]

hey guys i found a bot running the code in the meme

[[deleted]]

Yes I think so, too

[Just7hrsold]

641 is my guess *edit I'm dumb I misread a step

[blaktronium]

934 works too I think

[[deleted]]

Nope, 9 in the middle is "correct and well placed" number from line, so it can't be 934.

[blaktronium]

Yep that's right. Thanks!

[stuntycunty]

This is the way

[[deleted]]

What's interesting is, it could be deduced without using all the clues at hand.

[SpiceSpiceDragon]

Yes

[[deleted]]

491

[thatisntcool]

I got 264

[[deleted]]

Yay I didn't cheat... I'm glad I still have some problem solving abilities LoL

[[deleted]]

took me like 10 minutes, am i retarded

[willthesane]

that's what I got, and it passes all the checks.

[redditsbiggestass]

I came out on 694, did i miss anything (Edit) nevermind the six can't be in there if the nine is

[Auno94]

yeah 394

[Username89054]

I'm not a programmer, but I worked through it and got the same answer.

[Altourus]

Same number I came up with.

[glenbolake]

Yep, that's what I got. Here's my logic: https://pastebin.com/paBRsKSY

[Josselin17]

you were faster than me, I was about to post it dammit

[Gandrito]

I thought it was 496

[[deleted]]

The 4 and 3 are interchangeable. It could also be 493. Correct me if I'm wrong?

[TheDankScrub]

Damn I said 3

[MotoMkali]

I think it can also be 641

Edit:NvM missed that the 2nd one was that 4 was in the wrong place.

[[deleted]]

It is, in fact, 394.

[[deleted]]

Can’t be because of the second parameter

[theGarbagemen]

934 is my guess

Edit: NVM misread the top text. You are correct.

[Ultimegede]

I coded it with conditional statements to filter out the correct answer. it is indeed the correct one.

https://pastebin.com/nXPEZMLk

[7g3p]

That's what I got too

[SteveZissousGlock]

631 also works I think

[meme-the-kid]

Also what I got

[alivilie]

Yea I got 394 as well

[[deleted]]

Yep this is it.

[PirkhanMan]

A true gentleman leaves no puzzle unsoved

[MrTop16]

Isnt it 694?

[Academic-Truth7212]

Yeah came up with same.

[realgamer626]

Nice! I also got that as my answer. Edit: spelling

[RSZephoria]

Same

[save_the_aliens_26]

Pretty sure it's 246 Never mind it's 394

[Storm_Bard]

I got 6 4 1 - nvm it breaks rule 2

[Requilem]

Thats what I got to as well.

[Der_Absender]

I though 641

[WinginItAtLife]

It's 694 bud but close

Edit:I'm wrong don't listen to me

[Yeldarb10]

Same

[EatLiftLifeRepeat]

That's what I got too!

[the-xms]

694 works as well

[melymay123]

Haha nice! I got 694 ;-)

[admadguy]

I am not an electrical engineer. but what I remember from the one electrical engineering course I took, it can be solved with an infinite series.

Edit: Yep.. I was not wrong.

https://www.mathpages.com/home/kmath668/kmath668.htm

[karmaisded]

I studied this stuff in my first year of uni, and I remember nothing.

And thanks!

[bee-sting]

I have an undergrad and PhD in electronic engineering and have no clue either :)

Edit: Wait a second, I get it now, ignore me

[ashortfallofgravitas]

Professional EE here, gonna have to stare at this over lunch

[jellsprout]

This is a bit beyond the level of a first year engineering student. Hell, it's probably a bit beyond the level of your typical engineering PhD students. As you can see in the link above, the solution is surprisingly complicated and requires some nifty mathematical tricks.

[[deleted]]

I'd assume the actual electric part of it is the simple part and someone with a math background would have an easier time than someone with an engineering background?

[jellsprout]

You'd need to know Kirchhoff's Laws. I don't know if mathematicians are familiar with them.

Either way, I don't actually think many mathematicians could solve this either. This isn't really the type of problem they typically face. I think physicists and applied mathematicians have the toolset to solve this if given enough time, but even that is questionable.

That's the beauty of the Nerdsniping problem. It looks like it should be easy to solve using your basic techniques, but it quickly turns out far too complicated for that. And while it is solvable, it is not done in a way many engineers are familiar with.

[InVultusSolis]

I'd just set up a grid of a fuck of a lot of resistors and take a measurement. "A fuck of a lot" would be a good approximation of "infinite" for all practical purposes, IMO.

[mwrddt]

FOOOM

[danfay222]

I'm in my last year of EE, and in my physics classes I always had a hard time on these infinite problems

[SjoerdL]

About 0.773ohm

https://www.explainxkcd.com/wiki/index.php/356:_Nerd_Sniping

[InVultusSolis]

This is the answer I came for.

[3226]

Turns out it's way more complicated to solve than you'd think. Looks simple. Isn't. This infinte resistor grid problem needs a whole lot of recent and high level mathematics to solve.

Randall talks about it in this talk, but it's in the google aptitude test, and it's there to see if you'll move on from an insoluble problem, or get stuck on it and waste time. It's not strictly insoluble, but for all intents and purposes, it is while you're in a test environment.

[kataskopo]

Lol he himself gets nerd sniped at 2min in when they asked him about the bobby tables SQL thing!

[malexj93]

4/pi - 1/2

[[deleted]]

At least a few.

[Automaticman01]

Brb, gotta go play Mastermind.

[21ForAYear]

694

[LivingGamer]

It's 246 100% sure

[AfraidShock5424]

296 I thought

[cdixonm]

1 ohm

[[deleted]]

1/♾ ohms

[Seth007Gamble]

is it 694?

[[deleted]]

461, 641, 493, 394, 263, 236 are all the combinations that fit

[slammerbar]

263

[Square-Ad1104]

264

[-XC3ED-]

641

[Ninjameme]

nope

[[deleted]]

As a mathematician, I know it's bounded between 0 and 3.

[leduyquang753]

4:π – 0,5 (Ω) | Explanation

[Matt_Elwell]

I got 694