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.

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Discussion

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• Parts of the challenge you found unclear
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Answer 1

Minimal number of jumps to reach a square

Answer 2

Prefix code generator

Answer 3

Pseudo-Quantum Bogosort

Quantum Bogosort is as follows:

1. Quantumly randomise the list, such that there is no way of knowing what order the list is in until it is observed. This will divide the universe into O(n!) universes; however, the division has no cost, as it happens constantly anyway.

2. If the list is not sorted, destroy the universe. (This operation is left as an exercise to the reader.)

3. All remaining universes contain lists which are sorted.

Source

Given that we cannot destroy the universe, the next best thing is to destroy a thread!

The challenge is as follows: Make a new thread for each possible permutation of a list and if the list is not sorted, destroy the thread.

Rules

Input is a list of length 4 or less

Output is a sorted list and I guess the number of the thread that is sorted? This part is iffy...

This is standard code-golf

Answer 4

Inverse trigonometric functions

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Example equations using complex logarithm:

\$ \sin^{-1}(z)=-i \cdot \ln(\sqrt{1-z^2}+iz) \$

\$ \cos^{-1}(z)=-i \cdot \ln(\sqrt{z^2-1}+z) \$

\$ \tan^{-1}(z)=\frac{i}{2} \cdot \ln(\frac{1-iz}{1+iz}) \$

Answer 5

Volume of a squaricililinder

Inspired by an interestingly-shaped glass at a cafe.

WHAT THE HECK IS A SQUARICILILINDER!?!?!

A squaricililinder is a prism with a square at one end and a circle at the other. The circle is as small as possible while being able to fit the square at the other end inside.

The width of the glass increases at a constant rate as you go up it.

Now what's the challenge?

Given the height of a squaricililinder and the diameter of the circle on it, calculate the area of the squaricililinder.

How am I supposed to calculate it?

It's simple, all you need to do is plug in the height \$h\$ and the diameter \$d\$ to this simple formula: $$\small\underbrace{4\times\left( \int_0^h \int_0^{\frac d{\sqrt 2} }\frac yh\times\sqrt{ 1-\frac{x^2\times\left(6-4\sqrt2\right)}d } dx dy\right) + \left(\frac{d^2}2 \times h \right)}_\textrm{I hope I got the formula right...}$$ It was obtained by calculating the area of the cuboid inside and then doing some two-dimensional integrals on the circular parts.

Can you give me an example implementation?

Sure, here's an ungolfed and slow example in Python + sympy:

from sympy import *

x, y, d, h = symbols("x, y, d, h")

def calculate_area_of_shape(diameter: float, height: float) -> float:
    
    formula_in_integral = (y / h) * sqrt(1 - (((x ** 2) * (6 - 4 * sqrt(2))) / d))
    
    integral_part = integrate(integrate(formula_in_integral, (x, 0, d / sqrt(2))), (y, 0, h))
    
    actual_formula = 4 * integral_part + ((d ** 2) / 2) * h
    
    return actual_formula.subs(d, diameter).subs(h, height)

Anything else?

This is code-golf, so shortest code wins!

Answer 6

Median of Chi-Square

Output the IEEE-754 single-precision floating-point number represented by the following binary decomposition:

Sign, Exponent, Mantissa
0, 01111101, 11010001110110101101101

This is the most accurate approximation of the median of the chi-squared distribution \$\chi^2(1)\$, which is approximately \$0.454936423119572751942516646979649\$ in decimal. There is no known closed form of this value.

Answer 7

Sums of sum of divisors in sublinear time

Answer 8

Unique String Deletions

You are given a string s, where s.length <= 42, and an integer k, where k <= s.length. All regular test cases have totals < 2147483648, but bonuses exceed this value. If limited by int32, return modulo of value.

Return the count of all unique strings obtained by deleting k characters. Fastest algorithm wins. In case of a tie by algorithmic complexity, whoever has the most bonus cases wins.

Test cases: These are the sums of all f(s, k) from k=0 to k=s.length

"" = 1
"a" = 2
"aaaaa" = 6
"meow" = 16
"acacc" = 17
"cbcab" = 26
"abcacc" = 37
"cbabca" = 50
"alifra" = 63
"caadbac" = 87
"abbbacbb" = 78
"abbbbbabab" = 97
"doggaggy" = 112
"abbabacca" = 162
"abbbacbbaa" = 218
"isosceles" = 384
"armageddon" = 720
"123456789abcdef" = 32768
"supercalifragilistic" = 812760

Bonus cases: (Used as tiebreaker)

"arithmosesquippedaliophobia" = 80375252
"antidisestablishmentarianism" = 174600720
"pseudopseudohypoparathyroidism" = 644909314
"supercalifragilisticexpialidocious" = 11073277084
"hippopotomonstrosesquippedaliophobia" = 14891636776

Answer 9

Draw numbers as dice patterns

Answer 10

How sorted is this array

Given an array output the minimum number of swaps needed to sort that array

Examples

[1, 2, 3, 4, 5]   ->  0
[1, 3, 2, 4, 5]   ->  1
[5, 4, 3, 2, 1]   ->  2
[1, 3, 4, 5, 2]   ->  3
[2, 3, 4, 5, 1]   ->  4

[3, 5, 1, 11, 7, 3] -> 3

Rules

• You can assume that the elements of the array are positive integers
• There might be duplicate elements
• This is code-golf, the shortest code wins

Optional additional requirement

Solve the problem in \$O(n²)\$

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Meta

• Would you consider this challange to be a duplicate? My solution only asks for the number of swaps, which seems to be a much easier task than finding the actual pairs of indices
  These twp challenges I found are very similar but not exactly the same: sorting networks, swaps in bubble sort

Answer 11

Add two rational numbers... esoterically

Objective

Build a binary operator \$\star : \mathbb{Z} \times \mathbb{Z} \to \mathbb{Z}\$ such that, there exists a bijection \$i : \mathbb{Z} \to \mathbb{Q}\$ such that, for every integer \$M\$ and \$N\$, \$M \star N = i^{-1}(i(M) + i(N))\$ holds.

Or in mathematical terms, build a binary operator \$\star\$ that admits a group isomorphism from \$(\mathbb{Z}, \star)\$ to \$(\mathbb{Q}, +)\$.

I/O Format

Flexible. Standard loopholes apply.

Scoring

This is a fastest-algorithm challenge. The submission whose the asymptotic worst-case time complexity of \$\star\$ is the fastest wins.

The parameter \$n\$ for the time complexity is \$s(M) + s(N)\$, where \$s\$ is defined as follows:

• \$s(0) = s(-1) = 0\$.
• For every integer \$D > 0\$, \$s(D) = \lfloor \log_2 D \rfloor + 1\$.
• For every integer \$D < -1\$, \$s(D) = \lfloor \log_2 (-D-1) \rfloor + 1\$.

The shortness of your code is a tiebreaker. That is, this challenge is secondarily code-golf.

Notes and Rules

Note that each bijection \$i\$ induces \$\star\$ uniquely. As such, your submission must specify your choice of \$i\$.

Answer 12

Build the smallest self driving Car

code-golf

Your goal is building the smallest self driving car to get from A to B.

The car is a point mass of 1kg and has a steering wheel to turn left and right, as well as an accelerator pedal to accelerate and brake. Furthermore it is equipped with LIDAR: If 0° is the forward direction, it has a laser every 10° from -90° to +90°. Each of these lasers measures the distance to the next wall. The point A is where the car starts witz zero velocity, pointing north. The destination B is an area where the car has to stop to finish the trip (it can be facing any direction).

Your job is to write a function that is called every second, to steer your car to the B area, without crashing into the wall.

def car(lidar, speed):
    # lidar is an array of 19 floating point numbers
    # speed is an integer
    steering = ... # can be any integer from -3 to 3 and refers to a multiple of 10° (eg -2 means -20°) the car is turned in this step.
    acceleration = ... # can be any of [-1, 0, 1] and refers to the acceleration in `m/s` for the next step
    # first the car is turned by the indicated amount, then the acceleration is added to the current velocity, and then we take a velocity-sized step in the current direction

    return steering, acceleration

The function must be deterministic and a black box function, that is, it can only communicate to the outside world via the inputs arguments and the returned values. The function must be as small as possible (measured in bytes).

If the car crashes into a wall, it will be disqualified.

Map

the map will need to be determined it will be a closed non-self intersecting polygon. Here is an example but it will be a longer and maybe a little bit more complicated:

---

Discussion

• EDIT: I just remembered there was Lab Rat Race: an exercise in genetic algorithms where we did something similar. So maybe it would make sense to take the challenge in a slightly different direction.

• EDIT2: There is an almost identical challenge in http://janismac.github.io/ControlChallenges/ (go to the menu with the little squares and choose "Vehicle Steering" or "Vehicle Racing"). After playing around with this I think a combination of golfing code and time would be nice.

---

I'd obviously have to write a controller and come up with a good map that is doable with the velocity/direction constraints. Ideally with some graphical output for the participants to debug their car.

1. Shall there be multiple maps?
2. Are the discrete actions a good idea? (And are the ranges any good?) I think for the velocity it is nice so the car can come to a full stop in the target area.
3. Should the steering be limited when the velocity is higher?
4. Currently it feels like this will end up as just as a compression challenge i.e. who can hardcode a good sequence of steering inputs. I'm not sure this is all that fun. Are there other challenge modes or variations for this setting that would be more interesting? (The other thing I had in mind was giving the players a fixed code-budget and measuring how far they can get in the map.)
5. Should the cars be allowed to have some memory between each step? (e.g. limited to a certain number of bits) - after the update from above I think it would make sense to allow some (or maybe even an unlimited) amount of memory between each step. But still it would be nice to have some sort of restriction.

Answer 13

Transpose a multidimensional array

Answer 14

Golf a LaTeΧ math expression code-golf string parsing

Answer 15

Visualise the Euclidean GCD

Answer 16

Is this your answer? answer-chaining

NOTE: The scoring criterion for this is currently broken. I'll fix it at some point ™

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In this challenge, you must write an answer that distinguishes itself from all previous answers. No matter what input is passed in, it must output one of two consistent values. Your answer must output one value, marked as "truthy", when your answer's code is input, and the other value, marked as "falsy", when the code of at least one previous answer is input. Whichever value it outputs when anything else is input does not matter as long as it outputs one of the two values.

However, you are not only trying to distinguish your answer from others, but also to trick previous answers into thinking your source code is their own and outputting their truthy value.

Your answer's score is \$\frac{\text{byte count} + 2}{\text{tricked answers } \cdot \text{ answers that don't trick you}}\$, where "tricked answers" is the number of previous answers that output their truthy value when given your code, and "answers that don't trick you" is the number of previous answers for which your answer correctly returns the falsy value. Your answer must trick at least one previous answer and not be tricked by at least one previous answer.

For example, if the first answer was the Python program print(1), then a valid second answer would be the JavaScript function x=>x.includes('x'), which checks if the input string contains a x, returning true for itself, false for the singlee previous answer, and either true or false for any input string. As the previous answer prints a 1 when given this code, this would score \$\frac{18+2}{1 \cdot 1} = 20\$.

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First answer (will be posted along with the question):

1: Python 3, 8 bytes

print(1)

Try it online!

Outputs 1 for truthy and 0 for falsy.

Answer 17

Is it a Valid Crossword Grid?

Answer 18

Expected number of rounds for this labeling scheme

Answer 19

Smallest infinite irreducible program

code-golf code-bowling

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A typical constraint for code-bowling challenges, where the goal is to make your code as long as possible, is that your program must be "irreducible". I.e., no subset of characters can be removed from your program with it still being valid. If your code was xyz, none of x, y, z, xy, yz, or xz could do the same task as xyz. This makes it impossible to use comments, string literals, long variable names, or whitespace to pad out your code length, but through some trickery it's possible to design a program which can be made arbitrarily large while still being irreducible.

In this challenge, you'll try to golf the setup for this. Your submission will be a finitely sized "base" program, which is irreducible, and which can be increased to an arbitrarily high size through the addition of substrings at a chosen point (or set of points) in the program.

For example, a base program might look like wx()yz, and continue to function and be irreducible with the insertion of arbitrarily many abs in between the ()s (such as wx(ababab)yz). You can also require substrings to be inserted in multiple places at once (e.g., you might need a 1 to be appended to the program for each ab, so the previous example would look like wx(ababab)yz111).

Scoring:

Your score is the size in bytes of your base program. Your base program must be irreducible on its own; if the insertion of some minimum number of your chosen substring(s) is necessary for this, those must be included in the score.

Task:

Your irreducible program must do any one of the following tasks, of your choice:

• Truth machine: Take an input. If the input is 0, print 0 and stop. If the input is 1, print 1 indefinitely
• Arithmetic: Take two inputs, x and y. Print x + y².
• Constant output: Print the string Good morning!

You may write a program or a function. If you choose to write a function, instead of printing you may return the output. For the truth machine task, you must use an infinite list/iterator if you return a value; you must have some way of getting an arbitrary number of 1s out of the return value in finite time (so you can't just append 1s to a list infinitely, and return the list once the infinite loop would stop).

Answer 20

Find the fairest partition of a list

Answer 21

Make Code Printing X Without X

Answer 22

How many twisted corners?

Posted here

Answer 23

Sub-quadratic base conversion

Write a program that converts a positive integer given in base 10 to its base 2 representation.

Your algorithm must run in a complexity lower that \$O(n^2)\$

Rules

• You can assume that each arithetic operation (sum/multiplication/division/remainder/exponentation) has the running time of the fastest known algorithm, independent of the implementation that is actually used (This includes methods that you wrote yourself).
  • Addition can be done in linear time
  • Multiplcation/division/remainder run in \$ O(n \cdot \log(n))\$ where \$n\$ is the sum of the numbers of bits of the inputs ^*.
  • Exponentiation \$N^X\$ runs in \$O((n \log x)(\log(n)+\log(\log x)))\$ where \$n\$ and \$x\$ are the numbers of bits in \$N\$ and \$X\$ respectively.
  • If you know faster algorithms please link them in your challenge
• All built-in base-conversion/library methods for base-conversion are assumed to run in quadratic time in the input, even if the actual implementation is faster
• (... more rules will follow)

code-golf restricted-complexity

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^* The \$O(n log (n)) \$ multiplication algorithm assumes that both arguments have the approximately same size, for simplicity you may assume that the same complexity can be archived for arbitrary argument sizes (this may not be true in practice).

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Meta

• Is this a duplicate?
• Is there interest in a challenge of this form?
• Is my explanation clear?

Answer 24

Compute the Kimberling Sequence

code-golf

Introduction

The Kimberling Seqeunce is a sequence of sequences. Each sequence is defined in terms of the previous sequence and the previous stage number. At each stage, the numbers from the previous stage are rearranged as follows:

• For k in [1,...,i], write term i+k and then term i-k.
• Discard the ith term.
• Write the remaining terms in order.

We start with all positive integers at stage 0, so the first few rows look like this.

1  2  3  4  5  6  7  8  9 10 11
2  3  4  5  6  7  8  9 10 11 12
4  2  5  6  7  8  9 10 11 12 13
6  2  7  4  8  9 10 11 12 13 14
8  7  9  2 10  6 11 12 13 14 15

At each stage, the number on the diagonal is expelled (it is an open question as to whether every number is eventually expelled).

Challenge

Your program must take a positive integer n as input and output the integer expelled in forming the nth stage of the Kimberling sequence.

Answer the following questions for your readers.

Standard loopholes are forbidden. As this is code-golf, shortest program wins.

Example Input and Output

1 -> 1
2 -> 3
3 -> 5
4 -> 4
5 -> 10
6 -> 7
7 -> 15
8 -> 8
9 -> 20
10 -> 9
11 -> 18
12 -> 24
25 -> 2
100 -> 229
1000 -> 394
1001 -> 1274

More test cases from OEIS.

Sandbox Questions

This is my first code golf question, so I'm not sure what to ask other than is there anything that I can improve/need to fix before asking the main site?

Answer 25

Implement the "Wolontis" Function

While looking at old ALGOL documentation with someone else on Discord, this "famous" function popped up:

Although it’s mentioned in other language manuals of the era, such as Runcible and FORTRAN, we haven't managed to find any references to this function online — so let's change that.

The expression in the image is \$\frac{\sin x}{\sqrt{1-e^{-x^3}}}\$. Your task is to implement this function for positive inputs, as its value is undefined at \$x=0\$ and imaginary for negative \$x\$. Floating-point inaccuracies are permitted.

code-golf math

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Sandbox questions

• How accurate/precise should answers be required to be?
• What other tags should I add?
• Any other information I should include? e.g. would a graph be helpful?

Answer 26

code-golf number natural-language

Read a French number

We have Spell out numbers in French, Translate numbers to French and Telling time in French, but we were missing the reverse:

Challenge

Read a French expression, and output the corresponding integer.

Input

In true French, a French number expression is a list of French words separated by whitespace, and possibly by hyphens "-" and the word "et", such as "sept mille deux cent vingt-et-un".

For this challenge, you do not need to care about hyphens and the word "et": you are free to take input as a whitespace-separated string of words such as "sept mille deux cent vingt un", or as a list of single-word strings such as ["sept", "mille", "deux", "cent", "vingt", "un"].

All French words will be taken from the following list:

        'zero': 0, 'un': 1, 'deux': 2, 'trois': 3, 'quatre': 4,
        'cinq': 5, 'six': 6, 'sept': 7, 'huit': 8, 'neuf': 9,
        'dix': 10, 'onze': 11, 'douze': 12, 'treize': 13,
        'quatorze': 14, 'quinze': 15, 'seize': 16,
        'vingt': 20, 'trente': 30, 'quarante': 40, 'cinquante': 50,
        'soixante': 60,
        'cent': 100, 'mille': 1000, 'million': 1000000, 'milliard': 1000000000

Note that in correct French, "million" and "milliard" must take an -s in plural form, but for this challenge you do not need to care about that. "zéro" also must take an accent on the "e", but you do not need to care about that. "un" must be "une" in feminine form, but you do not need to care about that.

Also note that if we simply added "septante: 70, octante: 80, huitante: 80, nonante: 90" then we would be able to handle Belgian French and Swiss French, but for this challenge you do not need to care about that.

Output

Output one integer, corresponding to the French input number.

Conversion rule

Once the sequence of French words has been converted into a sequence of numbers, this sequence can be converted into one number by identifying the largest number in the sequence, then using one simple recurrence rule:

convert(left, largest, right) = convert(left) * largest + convert(right)

with of course the special cases that convert(empty left sequence) = 1 and convert(empty right sequence) = 0.

For instance:

"sept mille deux cent vingt un"
[7    1000  2    100  20    1]
[7] * 1000 + [2 100 20 1]
7000 + ([2] * 100 + [20 1])
7000 + (200 + ([] * 20 + [1]))
7221

Test cases

"sept mille deux cent vingt un"     ->  7221
"soixante douze cent vingt un"      ->  7221
"dix sept cent quatre vingt neuf"   ->  1789
"mille sept cent quatre vingt neuf" ->  1789
"trois mille neuf cent quatre vingt dix sept" -> 3997
"cent mille milliard cent trente sept million trois cent quatre vingt quinze mille huit cent cinq"
    ->  100_000_137_395_805
"zero"                 -> 0
"un milliard dix sept" -> 1_000_000_017
"mille"                -> 1000

Rules

• This is code-golf, the shortest code in bytes wins!

Answer 27

Generate the snowflake pattern sequence

A snowflake figure looks like this:

A few rules govern how many points each ring can have.

• The innermost ring must have between 1 and 8 inclusive points.
• Every other ring must have between 2 and 8 inclusive points.
• To ensure symmetry, every ring must have a integer multiple times as many points as the next smallest ring.

Valid snowflake sequences, from the smallest to the largest ring, include: 1,2,2,6, 2,4,8, 3,6, 8,8,8,8,8, etc.

Your task is, given a number, output the best configuration of rings.

If there are multiple solutions, find the most aesthetically pleasing one as follows:

• The one with the most unique ring sizes
• Unique ring sizes being equal, the one with the biggest smallest ring. Eg. 2,6 is better than 1,7.
• If the unique ring sizes and smallest ring are both equal, output the one with the smallest total number of rings.

If there are still multiple options, you may choose one arbitrarily.

Test Cases

Number	Pattern	Image
1	1
2	2
3	1,2
4	1,3
5	1,4
6	2,4
7	1,2,4
8	2,6
9	1,2,6
10	1,3,6
11	1,2,8
12	4,8
13	1,4,8

Answer 28

Parse nested absolute values

Part1

Part2

Answer 29

Implement a simple stack language

Answer 30

Simulate a Plant Cell quine code-golf

Now posted! (old drafts still in version history)