Sandbox for Proposed Challenges

Question

This "sandbox" is a place where Code Golf users can get feedback on prospective challenges they wish to post to main. This is useful because writing a clear and fully specified challenge on your first try can be difficult, and there is a much better chance of your challenge being well received if you post it in the sandbox first.

Sandbox FAQ

Posting

To post to the sandbox, scroll to the bottom of this page and click "Answer This Question". Click "OK" when it asks if you really want to add another answer.

Write your challenge just as you would when actually posting it, though you can optionally add a title at the top. You may also add some notes about specific things you would like to clarify before posting it. Other users will help you improve your challenge by rating and discussing it.

When you think your challenge is ready for the public, go ahead and post it, and replace the post here with a link to the challenge and delete the sandbox post.

Discussion

The purpose of the sandbox is to give and receive feedback on posts. If you want to, feel free to give feedback to any posts you see here. Important things to comment about can include:

• Parts of the challenge you found unclear
• Comments addressing specific points mentioned in the proposal
• Problems that could make the challenge uninteresting or unfit for the site

You don't need any qualifications to review sandbox posts. The target audience of most of these challenges is code golfers like you, so anything you find unclear will probably be unclear to others.

If you think one of your posts requires more feedback, but it's been ignored, you can ask for feedback in The Nineteenth Byte. It's not only allowed, but highly recommended! Be patient and try not to nag people though, you might have to ask multiple times.

It is recommended to leave your posts in the sandbox for at least several days, and until it receives upvotes and any feedback has been addressed.

Other

Search the sandbox / Browse your pending proposals

The sandbox works best if you sort posts by active.

To add an inline tag to a proposal, use shortcut link syntax with a prefix: [tag:king-of-the-hill]. To search for posts with a certain tag, include the name in quotes: "king-of-the-hill".

Answer 1

Implement bottom (encode)

Answer 2

Is the Skat null game safe? [WIP] skat code-golf

For everyone who knows the card game Skat. Did you ever wondered when playing a null game: is this really safe to win regardless the other player cards? Well, let's try to solve this question with code.

The Skat game

Skat is card game with 32 cards. There are four colours: Diamonds ♦️, Hearts ♥️, Spades ♠️ and Clubs ♣️. Each colour has: Ace, King, Queen, Jack, 10, 9, 8 and 7. Three players are playing, so each one get 10 cards. The remaining two cards are called Skat and remain covered. Before each game it is to decide which of the three players plays alone against the other two which play together. The alone player gets the possibility to exchange one or two of his cards against one or two of the covered cards in the Skat. More about Skat can be read on Wikipedia.

The null game

There are times when get so bad cards, i.e. no Aces and no Jacks, that they will indeed really good, namely when you can't make any points, not even a trick with the cards.

The task

Write a program that will determine if an input of ten cards of the 32 cards will guarantee that the player will win the null game, i.e. the player won't get any tricks regardless how the other 22 cards are distributed for the other two players and whether or not the alone player is in forehand. You can assume any reasonable input and output that suits you. For convenience a reasonably sorting of the cards can also be assumed.

One note to the forehand rule: it is assumed that the alone player wants to win so he or she won't sabotage the game with drawing an Ace or similar high cards.

Test cases

Let's assume an array of two character strings where the first represents the colour (D for Diamond, etc.) and the second the value (7, 8, 9, X, J, Q, K, A) E.g ['D7','D8','D9','H7','H8','C7','C8','CX','CQ','CA'] will result in true indicating that this null game cannot be lost.

[more to come]

This is code-golf so the shortest code wins.

Answer 3

Colorize a diff, unified format

Answer 4

Catch the fruit (Abandoned) graphical-output game

I feel that this is too complex to be a good code-golf question, and has too many things to specify for it to be anywhere near serviceable. Anybody willing to make this idea into a proper question can do so.

Implement a osu!catch style game.

Introduction

osu!catch is a rhythm game where the player moves a "basket" to catch "fruits" falling from the top of the screen to the beat of a song. Think pong, but with timing.

It is highly recommended to watch this video before reading the question.

Here's a gameplay example from Bubbler: [osu!catch] Hitsuji to Ojisan - XENO [Spec's Overdose]

Input

You are required to take the following inputs:

• Time: How long your program is supposed to run.

• Approach Rate: This is the speed at which the "fruits" are supposed to fall down.

• Beatmap: An array of [time, x position, value] triplets where:

  • Time: you must support time in seconds, at the very least. Higher precision is encouraged.
  • X position: Where it will fall from.
  • Value: The size of the "fruit" will decrease with it's value.

Gameplay

Play area

• The canvas must be in a 4:3 aspect ratio.
• The score must be displayed at the top of the screen, in the middle. You do not need to align it.
• The score starts at 0.
• Use a dark background(#222222, preferably).

The player

• The player must be of a rectangular shape, white in color.
• Height: 1/50 of canvas height, Width: 1/6 of canvas width.
• The player must be at the bottom of the screen, movable using any two keys of your choice.
• The player must have a "dash" button. Their speed must increase 0.5x when they hold the dash button.
• When the player collects a fruit, it must disappear, and it's value must be added to the score.
• When the player misses a fruit, there should be an indicative visual cue where the fruit fell.(a small red square, preferably)
• The player must be constrained within the canvas.

Fruits

• Fruit must be square in shape, and red in color.
• Fruits must fall from the top of the screen, outside the viewport(unless unsupported).
• Max fruit size is 0.1 × height. Size scales inversely with value.
• Fruit speed must be related to the approach rate i.e. Higher approach rate must make the fruits fall faster. You may do this however you like, but please be reasonable.
• The lower edge of the fruit must touch the bottom of the screen at it's time value.

Scoring

This is code-golf. Shortest answer in each language wins.

---

Meta

• Is the specification simple enough?
• I am planning on making a separate ascii-art challenge for this. Is that a better idea?
• Is the specfication clear?
• Any further feedback?

Answer 5

Which Ninjutsu am I casting? code-golfstring

Posted

Answer 6

Trilobaccis' speed

The challenge is inspired by this beautiful one: Speed of Lobsters. And it's similar to this other one: Is it a lobster number?.

The word Trilobacci is a blend of Tribonacci and Lobster.

About tribonacci, quoting Wikipedia:

The tribonacci numbers are like the Fibonacci numbers, but instead of starting with two predetermined terms, the sequence starts with three predetermined terms and each term afterwards is the sum of the preceding three terms.

Regarding lobsters and speed, they refer to this subreddit where people have fun editing the text of images to create new phrases.

The challenge

The challenge is to "blank out" the digits of given numbers (let's say a,b,c) using the digit of other numbers (say x,y,z) which you have to find by yourself, and then tell whether you could use all the digits from x,y,z to blank out some (or even all) of the digits from a,b,c.

Being more specific: given three positive integers in ascending order, which are necessarily part of a tribonacci sequence (at least the one they can generate), find the three numbers that generated the sequence and use them to blank out the original input numbers according to the lobsters rules.
Then output a truthy value if you used all the digits from the found numbers, or a falsy value if you are left with digits that couldn't be used to blank out the input digits.

For the numbers generating the sequence, I mean the the three smallest non-negative integers being part of the sequence.

Lobsters rule!

Start taking the first digit of the first number of x,y,z and blank out its first occurrence in the digits of a,b,c. Then proceed with the next digit from x,y,z looking for its first occurrence in a,b,c, starting from where you left.

Examples

Given

[ 13, 23, 43 ]

you'll find out that they are part of a sequence generated by

[ 1, 3, 3 ]

so then you can proceed at the speed of lobsters:

[ 1, 3, 3 ]   --->   [ 13, 23, 43 ]
               ||
              _||_
              \  /
               \/
[ X, 3, 3 ]   --->   [ *3, 23, 43 ]

[ X, X, 3 ]   --->   [ **, 23, 43 ]

[ X, X, X ]   --->   [ **, 2*, 43 ]

And in this case you output a truthy value because you used all the digits from [ 1, 3, 3 ].

The numbers [ 903, 1661, 3055 ] are also generated by [ 1, 3, 3 ], but the output for them is a falsy value:

[ 1, 3, 3 ]   --->   [ 903, 1661, 3055 ]
               ||
              _||_
              \  /
               \/
[ X, 3, 3 ]   --->   [ 903, *661, 3055 ]

[ X, X, 3 ]   --->   [ 903, *661, *055 ]

[ X, X, 3 ]   --->   [ 903, *661, *055 ] can't find any 3 after the last blanked digit

Input

Three integers. (One by one, into an array, as one or more a strings, split like bananas, etc.)
You can even take them in descending order if like.

Output

Choose a truthy and a falsy value and be consistent with them.

Standard rules apply for your answer, with standard I/O conventions, while default Loopholes are forbidden.

It would be nice if you could provide an easy way to try your program and possibly an explanation of how it works.

This is code-golf, the shortest wins.

Test cases

Soon...

Meta

• Any feedback / suggestion?
• I thought about considering the digits of x,y,z as always, but blanking out their occurrence in a,b,c from right-to-left, so that who participated to the previous lobster challenges would have to renew this part of the answer. Do you think it would be a good thing?

Answer 7

Challenge

Print all the Tamil characters in any order you like. They should be 12 vowels, 18 consonants and the special symbol ஃ .

Your code should not print anything except for those letters but it can print one letter per line.

The consonants are: க் ங் ச் ஞ் ட் ண் த் ந் ப் ம் ய் ர் ல் வ் ழ் ள் ற் ன்

The vowels are: அ ஆ இ ஈ உ ஊ எ ஏ ஐ ஒ ஓ ஔ

Shortest code wins

Answer 8

Generate a "Pi-ey" number

mathpifastest-codecode-golf

Generate the smallest integer of the form \$x^x\$ with \$10^{n-1}\cdotπ\$ digits, rounded down, given \$n\$. If there is no such number, take the nearest number that has as many digits of \$π\$ in its digit count. For example, if \$n=5\$, then the number of digits would be 31415. If there was no such number of form \$x^x\$, then take the nearest digit count similar to 31415, like 31414 and 31416.

If there are multiple values of \$x\$ that will work, whichever one is closer to \$3.1415926e3141...\$ will be the chosen value. For instance, if two solutions for \$n=5\$ were \$1.234e31414\$ and \$1.234e31416\$, we would select the former, as it is closer to \$3.1415926...e31415\$.

Test cases:

Rules:

• Shortest amount of bytes of code wins
• Please post the number of bytes as well as the runtime for \$n=5\$.
• It is recommended that you post your score (below), but is not required.

Scoring

• Your score will be based on your program time and length. \$\text{score} = \text{program length in bytes} + 10 \times \text{time to execute in seconds}\$

Answer 9

Compute the analysis spectrum

This is based on a task I had in work a few years back.

A diode-array detector (DAD) is a kind of chromatography detector which fires light into a sample and detects the strength of the light that passes through it at different wavelengths. From this you can determine, among other things, the contents or the purity of the sample.

Most detectors can only detect on one wavelength. A DAD however can scan across a spectrum of wavelengths, typically from 190nm to 650nm. From that spectrum we can then pick out the wavelengths that we're interested in. Maybe for our sample we want to analyse it at wavelengths 300nm, 350nm, and 550nm. These are called 'channels'.

Each wavelength may also have a bandwidth across which the signal strength is averaged. If we have analyse on wavelength 420nm, with a bandwidth of 10nm, the range for that channel would be from 415nm to 425nm (5nm lower, 5nm higher than the base wavelength). However, this bandwidth is optional.

The DAD we'll be working with does not take a set of channels, but rather we must provide it with a minimum wavelength and a maximum wavelength to detect across. This will be our task.

The Challenge

Write a program or function that, when given a collection of channels, determines the lowest and highest wavelength to analyse across for these channels.

For this challenge, a channel consists of an integer wavelength, and an optional integer bandwidth. The wavelength can be positive or negative, but the bandwidth is always positive.

Bandwidths can be odd numbers, but in that case you would then shrink it down to an even number.

The upper limit can be the same as the lower limit, but can never be smaller.

Also, you can safely assume that at least one channel is given to your code.

Example 1

Channel 1
Wavelength = 420
Bandwidth = 10

For channel 1, the base wavelength is 420 and the bandwidth is 10.

Channel 1's lower range is the base wavelength minus half of the bandwidth. In this case, it's 420 - (10 / 2) = 415. The upper range is the base wavelength plus half of the bandwidth: 420 + (10 / 2) = 425.

Answers: Lower = 415, upper = 425

Example 2

Channel 1
Wavelength = 394
Bandwidth = 19

Channel 2
Wavelength = 500
Bandwidth = N/A

For channel 1, the base wavelength is 394 and the bandwidth is 19. Because the bandwidth is an odd number, and our DAD cannot accept floating-point numbers, we can round it down to 18.

Channel 1's lower range is the base wavelength minus half of the bandwidth. In this case, it's 394 - (18 / 2) = 385. The upper range is the base wavelength plus half of the bandwidth: 394 + (18 / 2) = 403.

Channel 2 has no bandwidth, so it's range is just at its base wavelength: 500.

Comparing the channel ranges, channel 1 has the minimum lower limit with 385. Channel 2 has the maximum upper limit, with 500.

Answers: Lower = 385, upper = 500

Test cases

Test case 1:

Wavelength 1 = 400
Bandwidth 1 = N/A

Answers: lower = 400, upper = 400

-------------------------------------

Test case 2:

Wavelength 1 = 200
Bandwidth 1 = 15

Answers: lower = 193, upper = 207

-------------------------------------

Test case 3:

Wavelength 1 = 394
Bandwidth 1 = 19

Wavelength 2 = 500
Bandwidth 2 = N/A

Answers: lower = 385, upper = 500

-------------------------------------

Test case 4:

Wavelength 1 = 394
Bandwidth 1 = 40

Wavelength 2 = 500
Bandwidth 2 = 10

Wavelength 3 = 380
Bandwidth 3 = 5

Answers: lower = 374, upper = 505

Rules

The range that you must produce must consist of an integer lower limit and an integer upper limit. This particular DAD cannot accept decimal numbers, so while your code may accept and output floating-point types, the values themselves must be whole numbers.

Computing this range is important for other settings on the DAD. Therefore, you may not take just any input and return an extremely small lower limit and/or an extremely large upper limit. Your outputs must be based on your inputs.

Standard rules apply, including the default I/O rules. Similarly, default loopholes are forbidden.

Finally, this is code-golf so shortest answer in bytes wins.

Sandbox Questions

• Is the challenge itself too complex or too easy?
• Is the requirement for whole-numbered outputs valid, or does it seem a little bit arbitrary?
• Are the examples and the test cases useful?
• Finally, would this be an interesting challenge?

Answer 10

Print the nth sequence from oeis

The input is one natural number n - the sequence number

Your task is to put this numeric link https://oeis.org/A (example of a link with n = 1: https://oeis.org/A1), then you should get the html of this page and get the sequence from there

Examples:

n -> sequence
1 -> 0, 1, 1, 1, 2, 1, 2, 1, 5, 2, 2, 1, 5, 1, 2, 1, 14, 1, 5, 1, 5, 2, 2, 1, 15, 2, 2, 5, 4, 1, 4, 1, 51, 1, 2, 1, 14, 1, 2, 2, 14, 1, 6, 1, 4, 2, 2, 1, 52, 2, 5, 1, 5, 1, 15, 2, 13, 2, 2, 1, 13, 1, 2, 4, 267, 1, 4, 1, 5, 1, 4, 1, 50, 1, 2, 3, 4, 1, 6, 1, 52, 15, 2, 1, 15, 1, 2, 1, 12, 1, 10, 1, 4, 2
2 -> 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2, 1, 1, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 1, 2, 2, 1, 2, 1, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2, 1, 1, 2, 1, 2, 2
3 -> 1, 1, 1, 1, 2, 2, 1, 2, 2, 2, 3, 2, 2, 4, 2, 2, 4, 2, 3, 4, 4, 2, 3, 4, 2, 6, 3, 2, 6, 4, 3, 4, 4, 4, 6, 4, 2, 6, 4, 4, 8, 4, 3, 6, 4, 4, 5, 4, 4, 6, 6, 4, 6, 6, 4, 8, 4, 2, 9, 4, 6, 8, 4, 4, 8, 8, 3, 8, 8, 4, 7, 4, 4, 10, 6, 6, 8, 4, 5, 8, 6, 4, 9, 8, 4, 10, 6, 4, 12, 8, 6, 6, 4, 8, 8, 8, 4, 8, 6, 4
4 -> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
5 -> 1, 2, 2, 3, 2, 4, 2, 4, 3, 4, 2, 6, 2, 4, 4, 5, 2, 6, 2, 6, 4, 4, 2, 8, 3, 4, 4, 6, 2, 8, 2, 6, 4, 4, 4, 9, 2, 4, 4, 8, 2, 8, 2, 6, 6, 4, 2, 10, 3, 6, 4, 6, 2, 8, 4, 8, 4, 4, 2, 12, 2, 4, 6, 7, 4, 8, 2, 6, 4, 8, 2, 12, 2, 4, 6, 6, 4, 8, 2, 10, 5, 4, 2, 12, 4, 4, 4, 8, 2, 12, 4, 6, 4, 4, 4, 12, 2, 6, 6, 9, 2, 8, 2, 8
6 -> 1, 1, 2, 2, 3, 3, 4, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 10, 10, 10, 10, 10, 11, 11, 11, 11, 12, 12, 12, 12, 12, 13, 13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18
7 -> 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
8 -> 1, 1, 2, 2, 3, 4, 5, 6, 7, 8, 11, 12, 15, 16, 19, 22, 25, 28, 31, 34, 40, 43, 49, 52, 58, 64, 70, 76, 82, 88, 98, 104, 114, 120, 130, 140, 150, 160, 170, 180, 195, 205, 220, 230, 245, 260, 275, 290, 305, 320, 341, 356, 377, 392, 413, 434, 455, 476, 497, 518, 546
9 -> 1, 1, 1, 2, 2, 3, 4, 5, 6, 8, 10, 12, 15, 18, 22, 27, 32, 38, 46, 54, 64, 76, 89, 104, 122, 142, 165, 192, 222, 256, 296, 340, 390, 448, 512, 585, 668, 760, 864, 982, 1113, 1260, 1426, 1610, 1816, 2048, 2304, 2590, 2910, 3264, 3658, 4097, 4582, 5120, 5718, 6378

code-golf, internet

Answer 11

Posted

Answer 12

post

Answer 13

Introduction

Book cipher

A Book cipher is a very unique method of a encipher. Here's how's it done:

• You have a book / a document or a article (something full of text, the more pages of text the better).
• You have a message to convey (a secret, of some sort)
• You simply-put read trough the text and the secret message (may come from input, or reading it from 2 separate files) - split it into words (so, separate spaces, commas and [dots]) so, ',' , '.' and spaces is the only requirement, how is not really that hugely important and you keep the count of how many words there are in the text, now input the secret message (note, the secret's words must be in the text, so if you secret was "My Secret" then, the words "My" and "Secrets" must both exist in the text.) and output the position of the inputted secret message. (E.g if the word "My" was nearly at the first page, maybe the 20th Word in the text, the program should print out '20'. Same with the word "Secrets", if that maybe were later, (let say the 93th word in the text) then your program should print out '93'.

Note the data type of input and output:

output numbers: Integers.

Input numbers: Integers

( Excluding if the secret actually contains a number, then it does not need to be treated as a int. Can be a plus if it does but is not necessary.)

Mini Example:

document.txt - file that contains text.

Secret: "My Secret"

(in the text, this is the 20th and the 93th word) (Note, this is only a made up secret, it is not from a real file, or a real input) a more better example is below.

Program input:

You enter "My Secret"

Program output:

20

93

And, again - you enter those numbers(**Integers**):

20 93

Program outputs:

My

Secret

this is just to show how input and outputs are related to each other.

For reference (if needed) You have a Python3 implementation available at my GitHub page, to see a book cipher in action here: GitHub - Book cipher in Py3

• Why is this challenge interesting?

I personally think this is a educational (and interesting) challenge ( one might also exercise, because of how simple it might seem to make, but really took myself - literally years to even know how to implement this correctly)

Interesting article to get some background of what Cicada3301 is (not my site) - https://www.clevcode.org/cicada-3301/

Wikipedia: Cicada3301

I created this challenge both to, see other peoples methods of solving this (you are free to use any programming language!) and also - how long it would take others (For me, really I think it took more than 4 years actually - even in Python3. It looks simple but, for me - really not)

• A motivating fact: There are still so little info (especially on example codes) on the internet(at least by the time writing this challenge) about just, book cipher implementations

Challenge

I would highly suggest making dedicated functions for this challenge

• (instead of writing all code in the main() function - but it's totally fine to have it all in main!)

Operation:

Here's how the program should read, process, and output the result:

First, take the text (the book/document, with the lots of text, (not the secret)) and:

Note: The text can either be entered or read from a file. You choose this.

1. read it (From a file, or enter it as input)
2. split it into words (by, I.e detecting '.', spaces(' '), and commas ',') (Or if you already have split the input & are ready to move on to step 3, do that :) )
3. count the number of words.

Repeat this process with the Secret input part.

So, the input secret part should be:

• read it (from, again a file or enter it as input)
• split it (i.e if your input was "My Secret" - split it into words like so: "My" "Secret")

My Python3 implementation only separate spaces.

The Key sequence - this is the nth words your text contains, e.g the 93th word in above example "Secrets".

The winner will be chosen by how short the code is. (So, the shortest code = win)

Example Input and Output

example file used 'document1.txt'in this section is available at the GitHub page. as well as the Python3 file used in the example below.

The output of your program should match the output of the Python3 program.

Input:

python3 bookcipher.py

input text: a house with a Bob inside

Output:

you entered these words: ['a', 'house', 'with', 'a', 'Bob', 'inside']

2

3

5

2

0

30

Input again: (decrypting)

input key-sequence sep. With spaces: 2 3 5 2 0 30

a

house

with

a

Bob

inside

Answer 14

Subbasis. Generate. Discrete?

Objective

Given finitely many finite sets, interpret them as a subbasis to generate a space, and decide whether the resulting topology is discrete.

Introduction to Topology

Given a set \$X\$, a topology \$\mathcal{T}\$ over \$X\$ is a subset of the power set \$\mathcal{P}(X)\$ such that:

• \$\emptyset, X \in \mathcal{T}\$.

• For all \$\space \mathcal{U} \subset \mathcal{T}\$, \$\bigcup\mathcal{U} \in \mathcal{T}\$.

• For all \$Y_1, Y_2 \in \mathcal{T}\$, \$Y_1 \cap Y_2 \in \mathcal{T}\$.

Members of a topology are said to be open. So the rules above in plaintext are:

• The empty set and \$X\$ itself are open.

• The union of arbitrarily many open sets is open.

• The intersection of finitely many open sets is open.

Endowed with a topology, \$X\$ is said to be a (topological) space.

If \$\mathcal{T} = \mathcal{P}(X)\$, \$\mathcal{T}\$ is said to be discrete.

Basis and Subbasis

A subset \$\mathcal{B}\$ of the power set \$\mathcal{P}(X)\$ is said to be a basis (pl. bases) of a set \$X\$ if:

• For all \$x \in X\$, there exists \$B \in \mathcal{B}\$ such that \$x \in B\$.

• For all \$B_1, B_2 \in \mathcal{B}\$, there exists \$C \in \mathcal{B}\$ such that \$C \subset B_1 \cap B_2\$.

We take every subset \$\mathcal{U} \subset \mathcal{B}\$ and declare \$\bigcup\mathcal{U}\$ to be open to generate a topology \$\mathcal{T}\$. Note that \$\mathcal{B} \subset \mathcal{T}\$ always holds.

If we omit the second requirement, we have a subbasis of \$X\$. A subbasis generates a topology by also declaring the intersection of finitely many members to be open.

Input and Output

Given a set of finitely many finite sets \$\mathcal{S}\$, \$X\$ shall be implicitly defined as \$\bigcup\mathcal{S}\$. Note that by this, the first requirement for bases always holds.

The input/output format is flexible. In every case, inputs that don't fit in your input format fall in don't care situation.

Examples

Truthy

• \$\emptyset\$ (Generates \$X = \emptyset\$ and \$\mathcal{T} = \{\emptyset\}\$)

• \$\{\emptyset\}\$ (Ditto)

• \$\{\{0\}\}\$ (Generates \$X = \{0\}\$ and \$\mathcal{T} = \{\emptyset, \{0\}\}\$)

• \$\{\emptyset,\{0\}\}\$ (Ditto)

• \$\{\{1\}\}\$ (Generates \$X = \{1\}\$ and \$\mathcal{T} = \{\emptyset, \{1\}\}\$)

• \$\{\{0\},\{1\}\}\$ (Generates \$X = \{0,1\}\$ and \$\mathcal{T} = \{\emptyset, \{0\},\{1\},\{0,1\}\}\$)

• \$\{\{0\},\{1\},\{0,1\}\}\$ (Ditto)

• \$\{\{0\},\{1\},\{2\}\}\$ (Generates \$X = \{0,1,2\}\$ and \$\mathcal{T} = \{\emptyset, \{0\},\{1\},\{2\},\{0,1\},\{0,2\},\{1,2\},\{0,1,2\}\}\$)

• \$\{\{0,1\},\{0,2\},\{1,2\}\}\$ (Ditto)

Falsy

• \$\{\{0,1\}\}\$ (Generates \$X = \{0,1\}\$ and \$\mathcal{T} = \{\emptyset,\{0,1\}\}\$)

• \$\{\{0,1\},\{1\}\}\$ (Generates \$X = \{0,1\}\$ and \$\mathcal{T} = \{\emptyset,\{1\},\{0,1\}\}\$)

• \$\{\{0\},\{1,2\}\}\$ (Generates \$X = \{0,1,2\}\$ and \$\mathcal{T} = \{\emptyset, \{0\},\{1,2\},\{0,1,2\}\}\$)

• \$\{\{0,1\},\{1\},\{2\}\}\$ (Generates \$X = \{0,1,2\}\$ and \$\mathcal{T} = \{\emptyset, \{1\},\{2\},\{0,1\},\{1,2\},\{0,1,2\}\}\$)

Answer 15

Decode an 8086 MOD R/M

code-golfbitwiseparsing

I think this might be fun. Or, it might be torture, idk. 😛 If this is popular, I might add a sequel for the significantly more complex 32-bit encoding 😏

Time for a mini objdump.

An 8086 MOD R/M field is laid out like so:

MOD  REG  R/M |  OPTIONAL DISPLACEMENTS
mm   rrr  rrm | (iiiiiiii) | (iiiiiiii)
76   543  210 |  76543210  |  76543210

REG is a register. Quite unintuitively, the register names are not in alphabetical order.

Note that you can safely assume a word register, not a half byte register, and that the destination is a register.

REG |  0 |  1 |  2 |  3 |  4 |  5 |  6 |  7 |
Name| AX | CX | DX | BX | SP | BP | SI | DI |

MOD determines the length and format of the instruction.

MOD | FORMAT
 0  | [MEM] or [ADDR]
 1  | [MEM+/-disp8] (signed 8-bit immediate)
 2  | [MEM+/-disp16] (signed 16-bit little endian immediate)
 3  | REG

MEM is parsed as so:

MEM  |    0    |    1    |    2    |    3    |   4  |   5  |   6   |   7  |
Name | [BX+SI] | [BX+DI] | [BP+SI] | [BP+DI] | [SI] | [DI] | [BP]* | [BX] |
*when MOD==0, [BP] is replaced by an absolute 16-bit address.

Just [BP] is encoded as [BP+0].

I am going to represent MOD R/M as octal, and addresses/displacements as hex. It really bugs me how few people write it this way, as it makes much more sense.

So, for example:

MOD  r  r/m
 3   0    0
reg  |    |
    AX,  AX

 0   2    0
mem  |    |
    DX,[BX+SI]

 1   3   7 , 23
M+D8 |   |   |
    BX, [BX+0x23]

 2   2   1 , BC 6A
M+D16|   |    | /
    DX,[BX+DI+0x6ABC]

Rules:

• You may take your input as a packed integer, byte array, string in any mix of bases, or whatever. I'm not picky. I personally wrote them as mixed hex and octal.
• You will always get 3 bytes, however, in true objdump spirit, those extra bytes will be random. The first byte is all you need to determine the length.
• Not all cases will be the most efficient encoding.
• In the output:
  • It may be returned as a single string, or printed.
  • It is case insensitive
  • It can have excess spaces or tabs, but it must be on one line.
  • It can have an optional trailing newline
  • Displacements and addresses can be in any base, however, do note that displacements are signed two's complement and will be subtracted if negative. So, for 100 FF, AX,[BX+SI+0xFF] is wrong.
  • Leading zeroes and displacements of zero are fine.

Test cases (irrelevant bytes are in italics):

300 73 A2 -> AX,AX
312 01 82 -> CX,DX
337 3E 1C -> BX,DI
020 24 AF -> DX,[BX+SI]
137 23 6B -> BX,[BX+0x23]
066 34 21 -> SI,[0x1234]
166 00 10 -> SI,[BP+0x00]
221 BC 6A -> DX,[BX+DI+0x6ABC]
124 FF EF -> CX,[SI-0x01]
224 FF FF -> CX,[SI-0x0001]
240 00 00 -> SP,[BX+SI+0x0000]

Answer 16

Create a QR quine

(a "qruine" if you will)

Design a QR code that legibly spells with its pixels (or the space between them) the text that it scans to.

For example, this QR code scans to the letter A, and also spells out A in white:

It does not matter what the scanned and displayed text is; it does not have to be coherent or readable.

The winner is the person with the longest text.

Answer 17

Posted link

Answer 18

Is this code in the same language as my answer? (WIP)

Probably a bad idea, but the goal here is to output a truthy value if a given input string is valid syntax in the same language as your answer.

Answer 19

I don't care how it started, but I'm going to end it!

kolmogorov-complexity

---

Given a number between 0 and 10,000 (inclusive) as input, output that many arbitrary* printable ASCII characters, followed by the exact text:

I don't care how it started, but I'm going to end it!

_{* The arbitrary preceding text must not contain the ending text.}

You do not need to verify the input value.

Answer 20

Shortest and Asymptotically Fastest Sort of 3-Tuples

Tags: fastest-algorithmcode-golfsorting

Write the shortest and asymptotically fastest function or program that will sort a set of 3-tuples.

Input

Input is a set (or unique list, array, etc) of 3-tuples, containing positive integers.

Output

Output is a set (or unique list, array, etc) of 3-tuples sorted in the following way:

• The first elements of each tuple are monotonically increasing.
• For each value of the first elements, the second elements are monotonically increasing.
• For each value of the second elements, the third elements are monotonically increasing.

Additional Rules

• As well as a byte count, include the asymptotic time complexity spent by your program.
• Explanations are encouraged! (Especially for showing the time complexity)
• Standard loopholes are forbidden.
• Input and output is flexible, as long as each 3-tuple is individually identifiable.
• Scoring is time complexity, with byte length as a tie breaker.

Examples

Input - Output # Comment
[(1,2,3), (400,500,600), (0,0,0)] - [(0,0,0), (1,2,3), (400,500,600)]
[(1,0,255), (1,255,0), (1,10,123), (1,50,96)]
 - [(1,0,255), (1,10,123), (1,50,96), (1,255,0)] # sorted by second elements
[(1,0,255), (1,0,0), (1,0,123), (1,0,96)]
 - [(1,0,0), (1,0,96), (1,0,123), (1,0,255)] # sorted by third elements
[(1,0,255), (1,255,0), (1,10,123), (1,50,96), (2,0,255), (2,0,0), (2,0,123), (2,0,96)]
 - [(1,0,255), (1,10,123), (1,50,96), (1,255,0), (2,0,0), (2,0,96), (2,0,123), (2,0,255)] # sorting by first and second
[(1,0,255), (1,255,0), (255,23,232), (1,10,123), (1,50,96), (2,0,255), (2,0,0), (2,0,123), (2,0,96), (1,2,3), (400,500,600), (0,0,0)]
 - [(0,0,0), (1,0,255), (1,2,3), (1,10,123), (1,50,96), (1,255,0), (2,0,0), (2,0,96), (2,0,123), (2,0,255), (400,500,600), (255,23,232)]

Answer 21

First sequence with no square differences

Answer 22

Lists of power

code-golf kolmogorov-complexity

Generate the following list of lists.

[[0], [1], [2, 4, 8, 6], [3, 9, 7, 1], [4, 6], [5], [6], [7, 9, 3, 1], [8, 4, 2, 6], [9, 1]]

This is code-golf, so shortest answer (as measured in bytes) wins.

Answer 23

Sequential Multiplication Magic Squares

code-golf

(Inspired by this question for a 5x5 and this question for a 4x4 magic square on the Puzzling SE sites.)

For this challenge, a sequential multiplication magic square is an NxN square filled with numbers 1..N² where the product of any M-th row equals the product of the M-th column. That is, the product of the first row is equal to the product of the first column, the product of the second row is equal to the product of the second column etc.

For example, one such 3x3 square might be as follows, but other similar results are valid as well:

9 8 3
4 5 2
6 1 7

Notably, there is no such square for N=2.

Challenge

Given a side size N of 1 or larger, output a valid NxN sequential multiplication magic square, or any distinct falsy value if none exists.

Standard loopholes apply, any convenient input-output, this is code-golf so the shortest code in bytes wins.

Sample cases

1 → [1]

2 → any distinct falsy value

3 → [[9, 8, 3],
     [4, 5, 2],
     [6, 1, 7]]

4 → [[16,  3, 12,  4],
     [ 9, 10, 14,  1],
     [ 8,  7, 11, 15],
     [ 2,  6,  5, 13]]

5 → [[ 7, 16,  6,  3, 25],
     [ 5, 13, 22, 12, 24],
     [ 9, 11, 17, 14,  4],
     [20, 18, 21, 19,  1],
     [ 8, 10,  2, 15, 23]]

Answer 24

Three, Three, No

Answer 25

Syslog PRI Conversion

This is my first CodeGolf post, so I expect some errors my content.

The rsyslogd utility has been a tool used throughout time to handle and parse logs either over an IP network or even locally. As many of you might know, this tool utilizes the basic syslog protocol.

The syslog protocol handles both a Facility and a Severity level in one integer, called Priority. The formula to extract these levels is as follows:

Priority = Facility * 8 + Level

In this challenge, your task is to write an application that converts a Priority value from the syslog protocol into a human readable format. The application must take input from STDIN, and output both the Severity and Facility string associated with the numerical code.

The numerical code/type table is as follows:

Int     Severity
0       Emergency
1       Alert
2       Critical
3       Error
4       Warning
5       Notice
6       Informational
7       Debug

Int     Facility
0       kernel messages
1       user-level messages
2       mail system
3       system daemons
4       security/authorization messages
5       internal
6       line printer subsystem
7       network news subsystem
8       UUCP subsystem
9       clock daemon
10      security/authorization messages
11      FTP daemon
12      NTP subsystem
13      log audit
14      log alert
15      clock daemon
16      local0
17      local1
18      local2
19      local3
20      local4
21      local5
22      local6
23      local7

The format of the outputted text may be any style you like, as long as it retains its human readable characteristics.

Examples

mail system, Critical\n

mail system\n
Critical\n

mail system - Critical\n

mail system Critical\n

Example

Given a PRI value of 103, your program must output:

NTP Subsystem, Debug

The shortest answer in bytes wins!

Answer 26

Interpret the next answer

This is an answer-chaining challenge where the aim is to write an interpreter for a specific language ("language X") in another language ("language Y"). Languages X and Y must be completely distinct, that is they must not be different versions of the same language, nor the same language itself. The next answer should then write an interpreter for language Z in language Y, and so on.

Interpreters do not need to fully implement the language, just a Turing-complete subset. In order to be a valid interpreter, it must have some way of inputting a string of code and a number (potentially zero) of inputs. One example may be a function that takes the code and inputs as an argument.

You may not reuse languages (so each language will be in exactly 2 answers - as an interpreter and being interpreted). Different versions of languages count as the same language, so long as they are considered to be different versions of the same language (e.g. Python 2 and 3, or Seriously and Actually)

You must wait 3 hours between posting and cannot post twice in a row. The challenge ends after a week has passed with no new answers. Your score is equal to the number of answers you have posted, with a higher score being better

Answer 27

SSD optimize

Given \$n\$ pages, each page containing \$m\$ sectors, write three functions: (Here x and y are sectors)

1. insert(x) that stores the input(temporary sector) into a sector,
2. remove(x) that removes one, and
3. get(x) that return a sector containing the element.

You can call these functions:

1. copy(y,x) that copy a sector from x to y, and
2. clear(x) that clears the page containing x, can only be called \$k\$ times for each page.

There'll never be more than(can equal to) \$p\%mn\$ elements required to store. Your score is the numbers of call before you fail. Everyone can provide test case for any program.

\$n=256, m=16, p=75, k=100\$.

For example, if a solution don't do any clear and just place inputs into \$(1,1), (1,2), \cdots, (n,m)\$, someone else can write and remove till you use up all space:

insert\*3072, (delete, insert)*1025, get

The last get can't get anything and is a fail, so the score is 5122.

Highest score wins. Robber's winning criticia TODO.

Answer 28

Build a Markdown to HTML converter

code-golf string
The Stack Exchange network uses Markdown as the syntax for writing posts. For example, using a # at the beginning of a line creates a heading (<h1>) while two hashes ## creates a subheading (<h2>).
Your task is to write a program which takes input as a syntactically valid Markdown string and outputs its HTML equivalent. (This program might find use as a means to transfer SE posts to one's own website.)
The only Markdown "commands" you need to support are the backtick (becomes a tag named code, styling provided), the hashes (# becomes h1, ## becomes h2 and ### becomes h3), and the > (blockquote). The rest may be left intact.

For example, if the input is

# Some text
## Part 1
Lorem `ipsum` dolor sit amet
> consectetur adispicing

Then the output should be

<h1>Some text</h1>
<h2>Part 1</h1>
Lorem <code>ipsum</code> dolor sit amet
<blockquote>consectetur adispicing</blockquote>

Leading spaces are acceptable for the headings as they are mandatory in Markdown, but trailing spaces are not (you may assume the input has no trailing spaces). Except for the inline code, all commands will be displayed as blocks and will be on separate lines. For example

# Some text ## Another

is not a valid input because there is a block command on the same line as another block command. You may assume that the input contains no < or > except for blockquote notation, you must also follow the guidelines exactly, so no outputting HTML which renders the same result but in a different way.

Second test case:

### Subheading
> This is some heading with `code` in it.

becomes

<h3>Subheading</h3>
<blockquote>This is some heading with <code>code</code> in it.</blockquote>

This is code-golf, so the shortest answer in bytes wins.

Answer 29

Output a random pair of twin primes. Every pair should possibly appear and the program should have zero possibility to fall into infinite loop. Notice that we don't know if there are infinite many pairs so you need some fallbacks to avoid finding a not-existing pair.

Answer 30

Finding Distant Primes