# What is the Sandbox?

This "Sandbox" is a place where Code Golf users can get feedback on prospective challenges they wish to post to the main page. 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.

To post to the Sandbox, scroll to the bottom of this page and click "Answer This Question", or click on the "Add Proposal" link below. Click "OK" when it asks if you really want to add another answer. Write your challenge just as you would when actually posting it. 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.

To add an inline tag to a proposal use shortcut link syntax with a prefix: [tag:king-of-the-hill]

# xkcd-esque Reverse Code Golf

## Introduction

A new xkcd comic came out recently, seemed to be a fun challenge and a change from the usual code golfing.

So I set out on making this challenge!

## Challenge

Make a short snippet of code in any language which, when read out, sounds like 1 sentence of normal English literature (for example, Moby Dick in the comic).

## Rules

• The snippet doesn't have to run, so you are free to add statements which would not execute (for example: undeclared variables, functions, etc.). However, it must be syntactically correct.

• A word in this challenge is any sequence of letters considered as valid English as in a dictionary. Articles (a, an, the) are counted as words.

• To prevent too long answers, the maximum number of words will be fixed at 200 individual words. This includes operator expansion.

• The maximum length of any function or variable name will be 10 words.

• The expansion used for an operator must be specified in the answer.

• Imported and built-in functions are not considered as operators.

• Since this is reverse code golf, the answer with the most points wins.

Scoring criteria:

• Characters used to structure code (0): All kinds of brackets, statement terminators, whitespace, etc.
• Comments and String literals (0): To avoid making large comments/literals with actual literature
• Names of functions or variables (1 per character):
• Keywords (2 per letter): Using keywords in the story as valid syntax.
• Operators (2 per letter of expansion): For example, > is worth 2x13 (isGreaterThan).

# Examples

Valid:

try { throw IngTheBallAnd; } catch (Ing it) {}
// Worth 3x2 + 5x2 + 13 + 5x2 + 3 + 5 = 37 points

let myLife = "a quote";
// Worth 3x2 + 6 + 2x2 = 16 points ("=" used as "be")


Invalid:

// One does not simply write everything in a comment
// Worth 0


Hope this meets PPCG puzzle criteria :D

• Define "short" Otherwise answers could just go on and on to approach infinite score. – Adám Feb 28 '18 at 10:05
• How long may function/variable names be? – Adám Feb 28 '18 at 10:07
• How do we determine the exact expansion of operators? E.g. is * "times" or "multipliedBy"? – Adám Feb 28 '18 at 10:09
• So the APL function ×× would count as 28: (signOfTheTimes)? Indeed APL functions often read nicely as plain English. E.g. (?∘≢⊃⊢)¨(⊂⍳3)/⍨¨1+⊢ reads as "a random number up to (?) the length (≢) selects from (⊃) the value of (⊢) each of (¨) the entire (⊂) indices until (⍳) three (3) replicated (/) by (⍨) each of (¨) one (1) added to (+) the value of the argument (⊢). – Adám Feb 28 '18 at 10:26
• @Adám I'll edit my answer to answer these. As for APL, I guess my puzzle is no match for it :P – K3v1n Feb 28 '18 at 10:46
• @Adám I'd actually aim for english literature rather than procedure sentences – K3v1n Feb 28 '18 at 10:50
• What is a "determiner"? Some programming languages do not use white space. What is a word? – Adám Feb 28 '18 at 11:05
• "Context" determination of expansion is not an exact science. As long as your challenge has that feature, I predict it will be closed as "unclear what you are asking". – Adám Feb 28 '18 at 11:07
• Are built-in functions "keywords"? What about imported functions? – Adám Feb 28 '18 at 11:08
• @Adám Edited to answer. Determiners were meant to be Articles (a, an, the). Lack of whitespace is not a concern as long as it is readable. I mentioned the need for specifying the intended meaning of operators before, but it was a partial change. – K3v1n Feb 28 '18 at 12:13
• built-in functions are not considered as operators? Uh, what exactly is an operator then? Some languages use single letters as operators. I'm afraid this question makes far too many assumptions about the features of programming languages. A common mistake, but often hard to fix. Compare to the problems with atomic code-golf. – Adám Feb 28 '18 at 12:53
• There have been a few questions about reading code as sentences, e.g. 1, 2, 3. Because answers can't be objectively scored, those are popularity-contests. However those types of challenge have mostly fallen out of scope on the site and are very hard to get right, see the tag wiki for more infos. – Laikoni Feb 28 '18 at 12:56
• Hmm.... alrighty. I shall disband this puzzle. I hope someone can make a better puzzle with the comic, it ought to get its own challenge ;) – K3v1n Feb 28 '18 at 13:17
• No one have said that? Welcome to PPCG! – Weijun Zhou Mar 1 '18 at 0:05
• Note that this is called code-bowling on PPCG. Typically code bowling questions have strict scoring rules to avoid arbitrary score inflation which usually prevents large variable/function names. – Jo King Mar 1 '18 at 2:19

# Bees?

Inspired by SCP-3045

Write a program that takes the input, extracts all of the words, and looks for the word bee; then:

• If bee is not detected, pick sections of the text at random and delete them.
• If bee is detected, add instances of the word bee to the input such that it has significantly more bytes than the original input.

The program should then output these modifications.

• How much is significantly more? Why is it popularity-contest? – Laikoni Mar 18 '18 at 14:00
• Do X creatively pop cons have fallen out of scope. This will get closed instantly if posted on main. – Dennis Mar 19 '18 at 12:51

Move a window around the screen

Your code should open a new window that is at least 100 by 100 pixels in size. Once the window is open you should be able to move the window around the screen using the keyboard. The window should move smoothly but it doesn't matter how fast it moves.

• Is there anything else that could make this challenge a bit more interesting? Maybe a scoring method? – RamenChef Mar 26 '18 at 14:01
• @RamenChef I suppose the scoring method was meant to be by the code-golf rules. I could make the challenge more interesting maybe by insisting that you can type into the window? – user9206 Mar 26 '18 at 14:05
• What counts as a "window"? I think this might be quite hard to define objectively in a way which is OS-agnostic. – Peter Taylor Mar 26 '18 at 15:38

# Output a Random Bit

Your task is simple: print either 1 or 0.

Chosen uniformly randomly every time.

No, not your silly pseudorandom nonsense. No system calls. No reading /dev/urandom. The randomness has to be unpredictable (i.e. reliant on chaotic, impossible-to-reasonably-model natural phenomena, and not on some configuration of bits in your computer).

## Specifications

• It is OK to query a site such as random.org for your bit.
• Your program only needs to be runnable once per day (i.e. you can assume there is a 24 hour gap between executions). This is to work around the fact that sites like random.org often have rate-limits.
• If it only has to be run once a day, wouldn't millis() % 2 be truly random? – geokavel Apr 2 '18 at 3:22
• @geokavel No, because you can't assume that the calling actions will be random (e.g. I could always invoke the program at 25-hour intervals, meaning that millis() % 2 would always be a consistent value. – Esolanging Fruit Apr 2 '18 at 4:11
• Is a time cost of maybe read a file in nanoseconds allowed? – l4m2 Apr 2 '18 at 4:42
• In its current form, it appears to be impossible to define the validity criteria objectively. Temporary -1. – user202729 Apr 2 '18 at 6:39
• @user202729 If it were up to you, how would you define them? – Esolanging Fruit Apr 2 '18 at 6:45
• /dev/random seems to be really random. Is it allowed? – the default. Apr 2 '18 at 7:30
• @someone Wikipedia says it's a PRNG, and I've heard that system randomness tends to draw entropy from sources like startup times and user actions, so that wouldn't count. – Esolanging Fruit Apr 2 '18 at 7:42
• Would a HRNG such as RdRand work? – the default. Apr 2 '18 at 8:24
• ... I admit that my downvote/comment is not constructive, but I found absolutely no way to objectively define the challenge. – user202729 Apr 2 '18 at 14:02
• Maybe define "real random" as "not only based on xxx"(currently last state, calling current) – l4m2 Apr 2 '18 at 15:38
• @l4m2 That was what I was trying to imply by saying it shouldn't be pseudorandom. – Esolanging Fruit Apr 2 '18 at 18:47
• @EsolangingFruit but you need to define what's pseudo – l4m2 Apr 2 '18 at 18:52

# Let's play the too high too - low game!

TL:DR : write a code that plays the too high - too low game

Given this pseudo code function for the too high - too low game, write it in your language of choice. This is just to make the challenge work better across all languages. This code won't count in the final score. You may also change the function's name and any of its variable's name too.

function isRight(number, guess):  # where the number is the correct answer and the guess is your code's guess

if guess < number:            # if the guess is too low
return 0                  # return 0

else if guess > number:       # if the guess is too high
return 2                  # return 2

else if guess == number:      # if the guess is right
return 1                  # return 1

else:                         # if there is an error
return -1                 # return -1


# The challenge

Write a code, function, script, etc. that guesses the right number. The range of the "random" number will be between 0 inclusively and 100 exclusively. For the sake of this challenge, the "random" numbers will be the test cases. Note that hard-coding the test cases is banned.

# Scoring

This is how the score will be counted:

bytes = number of bytes in your code
tries = the sum of all the tries used to guess all the test cases

score = bytes + tries


# Rules

• Hard-coding the test cases if forbidden.

# Test cases

[0,2,4,13,19,21,26,33,38,42,48,50,51,56,66,69,74,75,80,89,98,99]

• For one, i'd say the randomness is unfair. If you manipulate the seed python is given, you can just have it output a known sequence. Alongside that, can't you just hardcode the testcase? EDIT: Hardcoding the test case is the only way to get a good score. – moonheart08 Mar 29 '18 at 16:38
• @moonheart08 would banning hardcoding the test cases help? – Dat Mar 29 '18 at 17:57
• "the sum of all the tries used to guess all the test cases" Won't this be the same for all answers (with the only difference being floor vs ceil when taking halve the previous guess (as in 75 & higher could result in a next guess of either 87 or 88).First guess will always be 50. Is it lower, guess 25; is it higher, guess 75. etc. etc. Btw, there are already a few Guess the number challenges: Here is one; and here is another one. – Kevin Cruijssen Apr 3 '18 at 12:54

# ♫ I see a window and I want it painted black ♫

Yes, I know this is a popular mishearing of the lyrics. But instead of a red door, I really do want an (application) window painted black.

Your standalone program should launch an application window at least 400x400 and fill it entirely with black. It doesn't need to be borderless, and it doesn't need to exit gracefully.

Running in a browser is insufficient because there are still elements of the window such as the address-bar and tab-bar that aren't painted black. You must paint the whole window black except for borders added by your window manager.

This is code golf. Standard loopholes apply. Additional challenge is to listen to The Rolling Stones while making your submission.

Here is an un-golfed Java solution:

#compile: javac BlackWindow.java
#run: java BlackWindow
import java.awt.Color;
import java.awt.Frame;

public class BlackWindow{
public static void main(String[] args){
Frame frame = new Frame("no colors anymore");
frame.setsize(400, 400);
frame.setLocationRelativeTo(null);
frame.setBackground(Color.Black);
frame.setvisible(true);
}
}

• What if my platform doesn't support windows that large? – Nissa Apr 20 '18 at 23:17
• What is the 400x400 measured in? Pixels? Does it qualify if I somehow emulate a screen with larger resolution? – user202729 Apr 21 '18 at 9:23
• Does making the whole screen black count? – user202729 Apr 21 '18 at 9:24
• Stephen then make the whole screen black? What kind of system doesn't support that? – Jared K Apr 22 '18 at 0:16
• user202729 i was thinking pixels – Jared K Apr 22 '18 at 0:16
• What if I am listening to The Feelies cover of the song? Do I get the bonus point? +1 from me for an unusual challenge. – JayCe Jun 11 '18 at 3:34

# Shorter coding in non-golfing language

Copper write a requirement, a sample program in a golfing language, and a required non-golfing language. Rob hack it with the required language, with fewer bytes of code.

I guess it'd be cuz it's sometimes hard to define which is "golfing language". Also is it a duplicate?

• If it's a cops-and-robbers, then it can't be a popularity-contest. I personally don't think this challenge would work out; first of all, it's virtually impossible to outgolf a golfing language using a non-golfing languages because most golfing languages can complete most reasonable tasks in fewer bytes than it takes a non-golfing language to even print Hello World. Also like you said, golfing/non-golfing is extremely difficult to define. I also don't think this challenge would be particularly interesting because you'd likely end up with a bunch of miscellaneous cops posts with all – hyper-neutrino May 2 '18 at 13:09
• sorts of random requirements, which is basically just going to be a bunch of questions that either exist on PPCG already or could be posted to PPCG main as its own challenge, without any robber posts because it would be basically impossible. – hyper-neutrino May 2 '18 at 13:09
• IMO this is well past the threshold of "Too Broad", so I would vote to close for that reason. – Peter Taylor May 2 '18 at 15:23

(Now I don't know what the name should be)

# Intention

I want to create a challenge based on dependent typing, feature that exists in Idris, Coq, Agda and the similiar.

# Text

You should create a function in dependently typed language (Idris, Coq, Agda, etc) so that:

1. The function will receive a string that denotes format.
2. The format string will have s or n, s means it will receive a string, n means it will receive a number. You can assume that there is no other thing in the string
3. Arguments is received in order. If there is type mismatch, the error must be reported on compile-time.
4. After all arguments is received, the function will return a string, that is list of all passed argument

For example

formatf "sn" "goods" 25
> "goods 25"
> Type error in compile time
formatf "ak" "Akangka" 25
> You can do anything.
formatf "nnn" 24 25
> Either type error or return a function expecting a number and return string (currying is almost universal in these languages)
formatf "ss" "Akangka" "Martin Ender" "Adám"
> Type error on compile time


This challenge is similiar to printf-style string formatting, the difference that the function in this challenge has to be type safe.

Note that you cannot use build-in function or macro to do this

# Discussion

1. What should be the name of this challenge?
• Any reason why full programs are not allowed? – user202729 May 2 '18 at 9:29
• What happens if the language is not compiled? – user202729 May 2 '18 at 9:32
• (if you didn't realize, it's not just some languages can't solve it, but in some languages your requirements don't make any sense. There are languages without functions, language with only monadic functions, languages without integers, language without macros, language where macros have different meaning than C #define, language without string (C), etc.) – user202729 May 2 '18 at 9:59
• If the string is possibly not known at compile time, how can it produce a type error at compile time? – Angs May 2 '18 at 10:04
• Personally I think it's a bit too similar to the challenge you linked.. The only difference is validating the input-type with the format.. In which case it would be better to have a challenge dedicated to that, as in: Given this format and a variable amount of other objects, check if the format and types of these objects match. In which case "%s: %i%%", "Percentage", 25 would be truthy, and "%s: %i%%", 123.45, 25 would be falsey. In addition, most languages are type independent, which can change during run-time based on their use.. 10.0 could be all three types in some languages.. – Kevin Cruijssen May 2 '18 at 10:07
• Suggested re-working of the problem: Given a pattern using only %s and %n (for number), slot in the given list of strings and numbers in the given order, but return a distinct value or throw an error if the given list doesn't fit right. – Adám May 2 '18 at 10:08
• @Angs dependent typing. In fact, this challenge is about dependent typing. – Xwtek May 2 '18 at 10:17
• @user202729 well, by compile-time, I mean about typechecking time. I specifically disallow dynamic typing, as one of the point of the challenge is to make the program fail to typecheck if %s format is supplied by integer, etc. – Xwtek May 2 '18 at 10:21
• @KevinCruijssen Indeed, not all language can do this challenge. After all the intention is on the dependent typing, which most programming language (but not Idris, Coq, etc) lack. – Xwtek May 2 '18 at 10:26
• @Adám nice suggestion. But the type-safe feature (i.e. all error is on type-checking time) is integral part of the challenge – Xwtek May 2 '18 at 10:28
• @Akangka I don't understand why my suggestion doesn't satisfy that. You get a list of strings and numbers and need to check against each tag in the format that you've been given the right tag. – Adám May 2 '18 at 12:12
• I think you should limit to some languages (perhaps extend the language list if needed), as the challenge does not make sense in other languages anyway. – user202729 May 3 '18 at 1:26
• @Adám I actually implement your suggestion, except the throw an error part. I make the challenge require the result is type error – Xwtek May 3 '18 at 2:03
• @Akangka I don't understand why you insist on language specific features like "type errors" and "compile time". Your examples do not show how to format ss, ns, and nn. You mention float dots, but floats are not part of the examples any more. – Adám May 3 '18 at 5:46
• @Adám thanks about float dots. About language specific features, I just want to create a challenge about dependent typing. – Xwtek May 3 '18 at 6:50

# Challenge:

Your challenge is to write a quine-like program that takes a string from stdin and gives two outputs: Output A is the input string. Output B is your source code.

# Output Formats:

You can send your outputs to stdout, stderr, and/or files. If A and B go to the same output, they must be separated by a newline. Having a newline at the beginning of your source doesn't count. You'd need to print that newline from your source and then another newline to separate A and B.

# Examples:

source: print($stdin+"\n"+codeThatGeneratesSource) input: Hello, World! ### Both outputs on stdout: Hello, World! print($stdin+"\n"+codeThatGeneratesSource)


### Separate Outputs:

stdout: Hello, World!

$hiworld = new hiworld; echo$hiworld->$print; ?>  # Alternate Example Answer format # My Oh so wrong and totally fake Hello world - PHP - Alt.Points(53) <?php class hiworld{public$printme = "Hello World"}
$hiworld = new hiworld; echo$hiworld->\$print;
?>


Attempted with:

50 pts: PSR-2 Foo's Enforcement Hook: Foo-Checker [http://foo.example.com] (Broke)

3 pts: PSR-2 Bar's Enforcement Hook: Bar-Checker [http://bar.example.com]

Deleted Version

• That just makes it better. – lilHar Mar 8 '19 at 23:29
• Hate as measured by votes, however, is a discrete value, and therefore objective. – lilHar Mar 8 '19 at 23:37
• While I disagree that pop cons need an objective criterion for voting (anything objectively measurable wouldn't need votes), pop cons are out of favour for that very reason. It is rare for a pop con to be welcomed. – trichoplax Mar 10 '19 at 10:00
• @trichoplax Fair enough on that. I'll change encouragement to just be on coding style. – lilHar Mar 10 '19 at 22:25
• The problem is mostly the popularity-contest tag, which are very hard to do correctly. For example, how do you define break as many coding conventions as possible? How do you define convention, especially for esoteric languages where there are no conventions? The amount of conventions broken also depends on the poster's and viewer's standards, and is therefore not objective. – Jo King Mar 12 '19 at 21:38
• If a voter agrees it violates all the listed coding conventions, upvote the code that violates the most while still functioning is still subjective. All conventions are going to be subjective, e.g. Proper indentation, does that mean 4 spaces or a tab? One voter might think one way, and another might think another way. In general, I think you've chosen a very subjective winning criterion, and short of listing and defining the conventions yourself, it's not going to become objective again. – Jo King Mar 13 '19 at 0:06
• I've removed my downvote and the related comment. – trichoplax Mar 13 '19 at 6:59
• The new scoring mechanism is still subjective, but a big improvement. What counts as a convention still seems like a grey area. Does it need to be from an official source, for some definition of official? Does it need to have been posted online prior to the posting of this challenge? Does it need to be stating that coders "must", "should", or something else? – trichoplax Mar 13 '19 at 7:05
• One way to make this objective would be as a language specific challenge, for example with something like JSLint. That way your score is the number of complaints triggered when running it through the linter, and highest wins. Only being able to compete in one language doesn't seem ideal, but I mention it as an example in case someone can come up with a more inclusive approach. – trichoplax Mar 13 '19 at 7:08
• "Whatever makes you feel dirty for having put it through your keyboard" and "Each answer should list and link to coding conventions it breaks" are mutually contradictory. – Peter Taylor Mar 13 '19 at 12:00
• @trichoplax I do like your idea of counting linter complaints to make it more objective, and feel that's on the right track. Maybe bringing some code-cleanup program into it, and seeing how much work it has to do? – lilHar Mar 13 '19 at 15:33
• I feel like this could work if one language was selected, with associated style guide/linter, and an objective scoring system made for that. Otherwise, you're comparing a lot of apples and shoes. – Spitemaster Mar 14 '19 at 16:36
• I know this probably isn't going anywhere, but the most 'official' python style guide is probably PEP 8. – Artemis Apr 6 '19 at 18:17
• @liljoshu You've got my upvote for what it's worth, though I agree this needs some improvements. – Artemis Apr 8 '19 at 22:35
• Something like codegolf.stackexchange.com/questions/172445/… might be ok – Gymhgy Apr 10 '19 at 3:04

The heights of Natural Numbers

Every number can be expressed as the product of itself and/or smaller numbers. This is a fundamental feature of our world.

For example 10 can be expressed as the product of 5 and 2, or as the product of 1 and 10.

9 can be expressed as the product of 3 and 3, or 1 and 9.

12 can be expressed as the product of 2 and 6. 6, in turn, can be expressed as the product of 2 and 3. It could also be the product of 3 and 4, and in turn 4 is the product of 2 and 2. Lastly there is 1 and 12.

7 can only be expressed as the product 1 and itself.

The numbers in the products are called factors. Every number has at least 2 factors, itself and 1. Numbers with only those two factors are called prime. Numbers with more than 2 are called composite.

These factors can be written as trees. The root begins with the number itself, and factors are written below, by adding branches to the root.

7 has 1 and 7. This is a short tree. It has one prime.

9 has 3 and 3. This is also a short tree, but it has two branches. It has two primes, but they are both at depth of 1 down the tree.

10 has 5 and 2. Again, short. Again, primes are at depth 1.

12 has 6 and 2, 6 has 3 and 2. This tree has two levels of height. Note that at the second level, every factor is prime, but at the first level, some factors are composite. 12 has also 3 and 4, and 4 becomes 2 and 2 - the tree looks similar to when using 6 and 2, this is called Isomorphic, which comes from the Greek language words for same shape.

In other words, every number has several trees of factors, and each tree has leaves that are prime factors. And every tree has a height, the number of branches one must travel between the root and the furthest leaf.

For example, every number has a tree of height 1. Itself and 1. So.

7 has height 1, because 1x7=7

9 also is height 1, because 3x3=9, and 1x9=9, are both of height 1.

12 is height 2. 3x2x2 becomes 3x4, which becomes 12. There are two branches between 12 and either leaf of 2.

But 12 is also height 1 because it has a different tree of height 1: 1x12=12.

16 is height 3, because 16 becomes 2*8 becomes 2*2*4, becomes 2*2*2*2. But 16 is also depth 1 because 1x16=16. However 16 is not depth 2, because no tree of it's factors has primes up two branches from the root.

Write a program that given an integer n, returns a sequence of the first 100 numbers that have prime factor trees of height n.

• The prologue about factors and primes is unnecessary-- we know what they are. A diagram would be nice. You didn't explicitly mention the rules for creating trees-- why can't 16 = 4x4 = (2x2)x(2x2), or 16 = 8x2 = (8x1)x2? Are depth and height the same? – lirtosiast Jun 29 '19 at 7:12

# Best Mile Time

## Introduction

Your friend has been trying to improve his mile time on. Unfortunately, he isn't very good at keeping a steady pace and constantly speeds up and then slows down. He usually runs for many miles at a time and wants to choose the fastest mile of his run to determine his mile time.

Given your friend's distance versus time, determine his fastest mile time for a contiguous mile stretch.

## Input

A list of distances (in miles) sampled at an even interval.

## Output

The length of the smallest interval during which a distance of at least one mile was traveled.

## Rules

• You may assume that the the total distance traveled is at least 1 mile.
• The mile time must be for a continuous time interval.
• Standard loop-holes are forbidden.
• Standard rules apply.
• This is , so the program with the smallest asymptotic time complexity wins!
• Ties will be broken by fastest run time.

## Example

### Python 3.7, O(n ^ 2)

Try it online!

from typing import List

def fastest_mile_time(distances):
"""Determines the fastest mile time from a list of distances.

Parameters
----------
distances : List[float]
The list of distances in miles.

Returns
-------
int
The length of the smallest interval during which at least one mile was traveled.
"""
intervals = []
for i in range(len(distances) - 1):
for j in range(i + 1, len(distances)):
if distances[j] - distances[i] >= 1:
intervals.append((i, j))
break

return min(map(lambda x: x[1] - x[0], intervals))

• @FryAmTheEggman how's this? – Billylegota Jul 19 '19 at 2:32
• Unless I'm missing something this is trivially O(n): keep two pointers into the list, advance them keeping them 1 mile apart, and keep track of the running minimum time. I'm downvoting, so ping me if I was mistaken or if this is updated so I can update my vote. – lirtosiast Jul 19 '19 at 2:52
• @lirtosiast O(n) is trivial. I just gave O(n ^ 2) as an example. However it isn't clear to me that O(n) is the lower bound. I think the fact that the sequence is monotonically increasing may be of some use (although I've yet to show that to be the case). – Billylegota Jul 19 '19 at 3:20
• The optimal solution is O(n). You need to iterate two pointers through the entire list one time to ensure that you have found the minimum valid difference. The range of time this will take ranges from Ω(n) to O(2n) in the optimized case. for(i=j=0;j<length;i++){for(;array[j]-array[i]<1&&j<length;j++){}minTime=min(minTime , j-i)} – fəˈnɛtɪk Jul 20 '19 at 17:00
• Consider a list where every element at even index 2n is n, and every element at index 2n+1 is either n+.5 or n+1. If there is an integer at an odd index, the fastest mile time is 1, otherwise it's 2. But we have no way of determining this without reading all n/2 odd indices. – lirtosiast Jul 20 '19 at 18:17
• @lirtosiast +1 thanks for such a clear example! – Billylegota Jul 21 '19 at 6:16

## Produce a self-reproducing data structure

Write the shortest code to produce a self-reproducing list, dictionary, array, and so on and so forth. That is, when you index any one of the logically-available items that belongs to the resulting data structure that you have produced, you get the same data structure when you compare the equality between the data structure before you indexed and the data structure after you indexed.

• In order to verify your code with automatically-provided constructions in programming languages, you should pick an operator that compares whether two values are equal (or does type-comparisons, if available).
• If your language does not provide an equality operator, you should simulate an equality operator yourself using operators like - or other operators that do the job of comparing values (as in Acc!, where an explicit comparison operator is not provided.)

## Example

This is an example of a validity/equality test of a possible solution in a Python REPL (when you have already produced a list, namely list, where it produces itself at its 0th item). This test simply compares the equality between the non-indexed list and the indexed list:

>>> list
[[...]]
>>> list[0]
[[...]]
>>> list==list[0]
True


However, if the result of the last line (the equality comparison) is not a truthy value in your language (for example False and 0 in Python), then your answer is invalid and should be improved.

## Rules

• Your program does not have to take input; neither does it have to explicitly output the data structure. However, your resulting data structure has to be accessible in some way.
• This is a contest; the shortest answer will win.
• In this challenge, the values on both operands in the equality check should have the same type.
• Your code (both your testing code and your producing code) should not produce any errors; any outputs to stderr are considered non-truthy values and demonstrates that your code is invalid.
• What does "compare it" mean? There are many many types of comparison one can perform, and they don't necessarily give the same result for the same values. – Peter Taylor Jul 24 '19 at 7:11
• @A__ For JavaScript, is it == or ===? Either way, people will be angry. – wizzwizz4 Jul 24 '19 at 13:16
• @A__ Because either the challenge is trivial (['']) or you're arbitrarily restricting a language. Work on your definition of "equality operator". – wizzwizz4 Jul 24 '19 at 13:46
• @A__ So, basically, you want (x=[])[0]=x? No clever tricks? Just a bog-standard recursive data structure? (Though, it might be interesting in languages where those aren't allowed.) – wizzwizz4 Jul 24 '19 at 14:07
• @wizzwizz4 In fact, your program is a clever trick that I have not thought of. Mine is 13 bytes, yours is 11 bytes. Yes, what I want is a bog-standard recursive data structure, as long as it is not a duplicate of another question. (My program is a=[];a.push(a)) – user85052 Jul 24 '19 at 14:10
• @U10-Forward 0 bytes – tjjfvi Jul 24 '19 at 14:32
• @tjjfvi I thought about that one, but I didn't think it'd be syntactically valid. It does, however, work. – wizzwizz4 Jul 24 '19 at 15:19
• @wizzwizz4 How do you know which language? – tjjfvi Jul 24 '19 at 15:31
• @tjjfvi I just assumed it was a language where the "null" / "undefined" singleton was indexable, returning the very same value. – wizzwizz4 Jul 24 '19 at 15:34
• @wizzwizz4 No, JS: window.window === window :) – tjjfvi Jul 24 '19 at 15:38
• @tjjfvi I read the challenge differently to you. I thought it meant "any one of the logically-available items". By this rule, (x={}).x=x is the shortest I can think of, other than the trivial case. – wizzwizz4 Jul 24 '19 at 15:53
• @tjjfvi Well i do it in Python so no such a thing called 0 bytes in python – U11-Forward Jul 25 '19 at 1:08
• Alternative: window["window"]===window – user85052 Jul 25 '19 at 4:06

# Recursive Sum Up The Digits

Produce the shortest code that sums up all the digits in a number, and after if it still has more than one digit, sum it up again and again until it's with one digit, example: 987 would become 6 since 9 + 8 + 7 is 24, whereas 2 + 4 is 6.

• I have the feeling I've seen this challenge before, but I'm unable to find it. It could be that I'm confusing it with two similar loose challenges, since there are more challenges where we continue doing something until a single digit remains, and there are also loads of challenges summing the digits of an integer. I'm not 100% sure anymore whether there is already one with both combined. – Kevin Cruijssen Aug 5 '19 at 6:37
• This is just "Given n output n % 9". – Peter Taylor Aug 5 '19 at 7:46
• @PeterTaylor Ah, now I remember where I've seen it before: here in the sandbox, and you (or someone else) made that same comment. :) – Kevin Cruijssen Aug 5 '19 at 12:24
• Isnt this just a duplicate of codegolf.stackexchange.com/q/1775/87923? – EdgyNerd Aug 6 '19 at 8:19
• @EdgyNerd It's related, but not a dupe. That challenge takes multiple integers as input simultaneously, instead of a single input. And it outputs the amount of iterations for each of those integers to become a single digit, instead of the resulting digit itself. In addition, it has rather cumbersome output-format.. So that challenge would result in 987 2 for input [987]. The core part of both challenges is the same though: continue summing the digits of an integer until a single digit remains. – Kevin Cruijssen Aug 6 '19 at 9:16

# Make it improbable... BUT NOT IMPOSSIBLE

You must make a program that outputs truly once in a while. However, making it have output falsy all the time is not acceptable.

## Rules

• Standard loopholes are forbidden.
• You may use any of accepted I/O formats.
• Your program must be possible to output a truly value.
• When not outputting a truly value, you may either output a falsy value or not output anything at all.
• You may output two or more values, however if it contains a truly value, then the output is considered truly.
• The probability of outputting a truly value must be at most 1/2.
• Your program must not take/use an input.
• Using non-deterministic but non-random(Such as getting the time) is prohibited. However, if date etc. is used in the builtin random function, it is allowed.
• The program must theoretically always terminate or stop outputting anything.
• You may assume that you have a fast enough computer and large enough memory.
• Your program should not be affected by raising the maximum value of a data type. You may still use unaffected constants.
• Data types must be following its spec: ie. for an unbounded arbituary precision integer type, you may assume that it can go as high as you want(but you are not allowed to increment until an error as in the rule above), but a double-precision floating-point format still has 22-bit fraction and 8-bit exponent.
• Score is calculated as: Pl-1.5l, where P is the probability and l is the byte length.

## Example(s)

JavaScript
P=0.1, l=24 => Score=23.534


The lowest score wins!

• So is it acceptable for just a program that always outputs truly? You need to define improbable. (I assume this probability must be at least lest than 1/2.) Providing a few examples will be helpful. So is there only output and no input? In addition, you need an objective winning criterion, which is a criterion that posts for this challenge will need to comply in order for it to be a valid answer. (Usually this criterion is making the source code shortest.) – user85052 Sep 24 '19 at 13:37
• Sorry, I posted this incomplete. – Naruyoko Sep 24 '19 at 16:14
• I don't think your scoring method works particularly well, unless I'm making an error. For any $l > 1$ your score cannot be less than 1. Achieving a score arbitrarily close to 1 is relatively easy. So the only way to beat that is to have a one or zero byte solution. It is easy to make the probability increase exponentially with linear code additions. It might be necessary to penalise length massively, like $P \times e^{l!}$, to avoid similar problems. – FryAmTheEggman Sep 24 '19 at 18:39
• I see. I guess P^l^k is too penalizing but Pk or Pe^k is too forgiving. Pe^l! looks simple enough but is is the middle so it may work. – Naruyoko Sep 24 '19 at 20:11
• The problem with any of scoring methods for this challenge is that it is possible for any increasing computable function f, a program with length l can have P around 1/f(l). The only non-broken formula could be uncomputable, i.e. P/BB(l), where BB is the busy beaver function. – Naruyoko Sep 24 '19 at 20:15

# I reverse the source code, you keep the output

Yet another blatant rip-off of a rip-off of a rip-off of a rip-off. Go upvote those!

Your task, if you wish to accept it, is to write a program/function that outputs/returns its own output. The tricky part is that if I reverse your source code, the output must be preserved.

# Examples

Let's say your code is ABC and the corresponding output is XYZ. If I run CBA, the output must also be XYZ

• What's to prevent a trivial solution of just 1 in many (many) languages? – AdmBorkBork Sep 25 '19 at 18:30
• Or trivial comment abuse? – S.S. Anne Sep 25 '19 at 20:39
• @JL2210 This works in codegolf.stackexchange.com/questions/193315/… print("ABC")#("ABC")tnirp – gadzooks02 Sep 26 '19 at 15:21
• @AdmBorkBork This works in codegolf.stackexchange.com/questions/193315/… too: 1 is the reverse of 1 – gadzooks02 Sep 26 '19 at 15:22
• And to both of you: why did these not stop that code golf becoming a challenge? – gadzooks02 Sep 26 '19 at 15:23
• I didn't say it couldn't be a challenge. I just wanted to point out that this is trivial in many languages. And for what it's worth, I downvoted the challenge you linked for the same reason. – AdmBorkBork Sep 26 '19 at 15:48
• @gadzooks02 That challenge requires you to reverse the input. The input can be anything in that challenge. – S.S. Anne Sep 26 '19 at 15:49
• @JL2210 Ah yes. Would preserve the input work better? – gadzooks02 Sep 26 '19 at 16:02
• No, then it would be trivial in Bash and BrainFuck and C and, well, you get the point. – S.S. Anne Sep 26 '19 at 16:26
• @JL2210 Yes, OK. Do I need to do something if I've decided against a challenge? Delete the post? – gadzooks02 Sep 26 '19 at 16:29
• No idea. Read over the guidelines, they might help. – S.S. Anne Sep 26 '19 at 16:31