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

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Discussion

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• Parts of the challenge you found unclear
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Answer 1

Is this a Freeman Dyson Number?

Background

From this Popular Mechanics article

One day, in a gathering of top scientists, one of them wondered out loud whether there exists an integer that you could exactly double by moving its last digit to its front. For instance, 265 would satisfy this if 526 were its exact double – which it isn’t. After apparently just five seconds, Dyson responded, “Of course there is, but the smallest such number has 18 digits.”

Challenge Write a program that, when given a base ten number that is at least 18 digits long, moves the last digit to the front and checks if it is doubled as a result.

I/O
Input can be any 18 (or longer) digit integer. Any leading digit must be larger than zero.

Output
The original number with the Dyson transform (last digit moved to the front) and any truthy/falsey value (if that's a digit, it must have a delimiter).

Test Cases/Sample I/O

111111111111111111 -> 111111111111111111,false
100000000000000002 -> 210000000000000000 **F**
123456789123456789 -> [912345678912345678,0]
42105263157894736842 -> 24210526315789473684👎
808080808080808080808080808016 - 680808080808080808080808080801-NO
246802468024680246802468024680246802 -> false224680246802468024680246802468024680
105263157894736842 -> true,210526315789473684
315789473684210526 -> (T:5315789473684210526)
26315789473684210526315789473684210 -> 52631578947368421052631578947368421👍

etc...

code-golf, so shortest answer in bytes (by language) wins.

Answer 2

Posted

Tile the plane with squashed hexagons

Answer 3

Compress a grandmaster chess position code-challenge test-battery

Background

Compress a position from a grandmaster chess game to as few bits as possible on average. A strong submission will probably use that these positions come from real games by top players, and so will make chess sense and strategic sense, rather than just being random legal chess positions. As illustration, a study found that grandmasters do well at memorizing positions from real games using "chunking" but with only perform at novice level memorizing random boards.

The is related to but different from Smallest chess board compression, which scores on the worst-case scenario, and Smallest chess game compression, which compresses full games. (Sandbox: Let me know if this is too similar)

Task

You must write a compressor, which maps a chess position onto a sequence of bits, and a decompressor that returns its to the original position. You can vary the length of the bit sequence by position, and this will likely be important to getting a good score.

The position to compress will just be a the placement of pieces on the chess board. You do not to encode whose move it is, castling rights, or en-passant. It will be given in FEN string format with only the piece placement part, for example:

2krn2r/pppb4/4pq2/3pN2p/5P2/2PBP3/PP4P1/R2QK2R

Each letter corresponds to a piece (pawn="P", knight="N", bishop="B", rook="R", queen="Q", and king="K"). White's pieces use uppercase letters and Black's are lowercase. Slashes separate the descriptions of each of the rows from top to bottom, that is the 8 files doing from 8 (where black's pieces start) to down to 1. Numbers are used for blocks of that many empty spaces that are horizontally adjacent.

Scoring

You will be scored on the average length of your compressed bit sequence on 10,000 random game positions. They will chosen at random from games played by grandmasters, restricted to move 5 or later. [Will work out more details when generating this data.]

This Pastebin (TODO) contains 10,000 FEN strings to use as a training set that you can use to get a preliminary score. The final score will be based on a separate secret test set of 10,000 FEN strings.

Your code must correctly decode every game in the position. Be sure that it can handle all positions, such as ones with weird underpromotions, which might appear in the test set but not the training set. (Sandbox: How to handle submissions that break this? A default penalty score for games failed? Ask to resubmit?)

Your compression and decompression must complete within 5 minutes on all the games. (Sandbox: Allow to compress all games at once? Do one game at a time but store state to allow "learning"? Include a memory limit?)

The length of your code is immaterial to this challenge.

Answer 4

Permutation primes code-golf decision-problem permutations prime

A permutation prime is a prime such that at least one of its uniquified permutations (not equal to itself) of its digits is a prime.

Given a number, check if this number is a permutation prime.

Reference program

Here is a reference program I made.

Answer 5

The golfing skills are strong with this one code-golf string

Task

Consider the base string s = "The golfing skills are strong with this one", an adaptation of the quote "The force is strong with this one" by Darth Vader, an infamous character of the Star Wars saga (sandbox, am I correct?).

You have to output the string s with as many characters as there are bytes in your source code. If your code is longer than s, extend s by concatenating it repeatedly as many times as needed.

Your program must be non-empty.

Input

You may or may not take the string s as input for your program. (Sandbox, maybe it is more interesting to not allow the string as input?)

Output

A string as specified in the Task.

Answer 6

Halting problem for simplified Brainfuck code-golf decision-problem

Given a simplified Brainfuck program, you must determine whether it halts. Your program must always halt in finite time on valid inputs.

Simplified Brainfuck is a language that operates on a zero-initialized tape that is infinite in both directions. All cells contain integers from 0 to 255, and operations are performed modulo 256. There are the following instructions:

+ increment the current cell
- decrement the current cell
< move 1 cell to the left along the tape
> move 1 cell to the right along the tape
[ if the current cell is zero, skip past the next ]
] go to the previous [

Loops ([]) can't be nested.

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

Answer 7

Posted: Stepping Through Time

Answer 8

Quickly calculate \$ n! \bmod p \$ fastest-codefactorial

The idea is extremely simple: Given two positive integers \$ n \$ and \$ p \$, calculate the result of \$ n! \bmod p \$, where \$ p \$ is a prime.

Scoring

Your score is the highest \$ p \$ you can achieve within \$ 10 \$ seconds, by running the program \$ 10 \$ separate times. More specifically, each run-through will contain two inputs \$ n \$ and \$ p \$. You are to solve \$ n! \bmod p \$, where \$ n \$ is a random number in the range \$[1, p]\$.

You must use this program to generate the \$ 10 \$ test cases. So for example, if \$ p = 13 \$, the test case would look like this:

n, p
9, 13
3, 13
10, 13
13, 13
7, 13
13, 13
8, 13
9, 13
6, 13
4, 13

Rules

• Make sure that each test case is run separately, meaning you are not allowed to make use of previous test cases
• Multi-threading is disallowed
• Official times will be tested on my machine; make sure to include specifcations on how to run it

This is fastest-code, so the highest score wins!

Sandbox

• Any loopholes that need to be addressed?
• Is there an easy, trivial solution to this?

Answer 9

Cheat activated

Background

The game Grand Theft Auto: San Andreas went down to history also thanks to its wide selection of cheats. They're almost 90 and anyone who has ever touched this game, no doubt he tried them all!
One cheat is activated (on PC) typing in-game a secret keyword, and then boom, a jet pops out of thin air or perhaps all pedestrians look like Elvis Presley or some other rowdy effect...

They always come with this confirmation message:

Rockstar choosed to store them hashed, so due to collision, in addition to the intended ones there are many other strings that trigger every cheat.

Therefore I propose to solve this downside!

Task

Write a full program that prints CHEAT ACTIVATED if and only if the last part of a string is a cheat code.

Cheat codes

THUGSARMOURY
PROFESSIONALSKIT
NUTTERSTOYS
INEEDSOMEHELP
TURNUPTHEHEAT
TURNDOWNTHEHEAT
PLEASANTLYWARM
TOODAMNHOT
DULLDULLDAY
STAYINANDWATCHTV
CANTSEEWHEREIMGOING
TIMEJUSTFLIESBY
SPEEDITUP
SLOWITDOWN
ROUGHNEIGHBOURHOOD
STOPPICKINGONME
SURROUNDEDBYNUTTERS
TIMETOKICKASS
OLDSPEEDDEMON
DOUGHNUTHANDICAP
NOTFORPUBLICROADS
JUSTTRYANDSTOPME
WHERESTHEFUNERAL
CELEBRITYSTATUS
TRUEGRIME
ALLCARSGOBOOM
WHEELSONLYPLEASE
STICKLIKEGLUE
GOODBYECRUELWORLD
DONTTRYANDSTOPME
ALLDRIVERSARECRIMINALS
PINKISTHENEWCOOL
SOLONGASITSBLACK
FLYINGFISH
WHOATEALLTHEPIES
BUFFMEUP
LEANANDMEAN
BLUESUEDESHOES
ATTACKOFTHEVILLAGEPEOPLE
LIFESABEACH
ONLYHOMIESALLOWED
BETTERSTAYINDOORS
NINJATOWN
LOVECONQUERSALL
EVERYONEISPOOR
EVERYONEISRICH
CHITTYCHITTYBANGBANG
CJPHONEHOME
JUMPJET
IWANTTOHOVER
TOUCHMYCARYOUDIE
SPEEDFREAK
BUBBLECARS
NIGHTPROWLER
DONTBRINGONTHENIGHT
SCOTTISHSUMMER
SANDINMYEARS
KANGAROO
NOONECANHURTME
MANFROMATLANTIS
LETSGOBASEJUMPING
ROCKETMAN
IDOASIPLEASE
BRINGITON
STINGLIKEABEE
IAMNEVERHUNGRY
STATEOFEMERGENCY
CRAZYTOWN
TAKEACHILLPILL
FULLCLIP
IWANNADRIVEBY
GHOSTTOWN
HICKSVILLE
WANNABEINMYGANG
NOONECANSTOPUS
ROCKETMAYHEM
WORSHIPME
HELLOLADIES
ICANGOALLNIGHT
PROFESSIONALKILLER
NATURALTALENT
OHDUDE
FOURWHEELFUN
HITTHEROADJACK
ITSALLBULL
FLYINGTOSTUNT
MONSTERMASH

Input

• A string \$s\$ over the alphabet:
  [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z]

Output

• Print CHEAT ACTIVATED if there exist a cheat code \$c\$ such that \$c\$ is a suffix of \$s\$
• Nothing otherwise

This is code-golf, so the shortest code wins.

Answer 10

Convert an integer to Chinese numerals

codegolf number integer unicode

Your task is to convert an integer from 1 to \$10^{52}-1\$ (inclusive).

The characters from 1 to 10 with their Unicode code points are:

一 1 U+4E00
二 2 U+4E8C
三 3 U+4E09
四 4 U+56DB
五 5 U+4E94
六 6 U+516D
七 7 U+4E03
八 8 U+516B
九 9 U+4E5D
十 10 U+5341

Number greater that that are composed like this:

十一 11
十二 12
...
二十 20
二十一 21
二十二 22
...
百 100
百一　101
...
百十 110
...
百九十九 199
二百 200
...
九百九十九 999
千 1000
...
九千九百九十九 9999
一万 10,000

This is where it gets interesting, because numbers bigger than 10,000 are groups in groups of four, expressed with 十, 百 and 千. These are the powers we're going to use in this challenge:

十 10 U+5341
百 100 U+767E
千 1000 U+5343
万 10^4 U+4E07
億 10^8 U+5104
兆 10^12 U+5146
京 10^16 U+4EAC
垓 10^20 U+5793
秭 10^24 U+79ED
穣 10^28 U+7A63
溝 10^32 U+6E9D
澗 10^36 U+6F97
正 10^40 U+6B63
載 10^44 U+8F09
極 10^48 U+6975

Let's go through an example with 123456789123456789 as the input (other algorithms are possible)

• identify groups of four digits, starting from the right: 12,3456,7891,2345,6789
• convert each group: 十二 三千四百五十六 七千八百九十一 二千三百四十五 六千七百八十九
• insert the appropriate multipliers: 十二京三千四百五十六兆七千八百九十一億二千三百四十五万六千七百八十九

Notes

• A leading ー MAY be dropped before 千 and 百 and MUST be dropped before 十.

IO format

The input can be an integer in any reasonable format. You can use a string/sequence of characters or a number type, if your language supports it. 128-bit numbers are not large enough, by the way.

Testcases

input output
1 一
2 二
3 三
4 四
5 五
6 六
7 七
8 八
9 九
10 十
15 十五
20 二十
31 三十一
100 百
123　百二十一
1000 千
8346 八千三百四十六
10000 一万
50010 五万十
100000 十万
123456789123456789　十二京三千四百五十六兆七千八百九十一億二千三百四十五万六千七百八十九
1234567891234567891234567891234567891234567891234567 一千二百三十四極五千六百七十八載九千百二十三正四千五百六十七澗八千九百十二溝三千四百五十六穣七千八百九十一禾予二千三百四十五垓六千七百八十九京一千二百三十四兆五千六百七十八億九千百二十三万四千五百六十七

Standard code-golf rules apply. The shortest code in bytes wins.

References

• https://en.wikipedia.org/wiki/Japanese_numerals
• This online converter seems to work well: https://www.sljfaq.org/cgi/numbers.cgi
• The Japanese dictionary jisho.org can convert Japanese numberals to western notation

Answer 11

The Double-Castle Numbers™ code-golfnumberbase-conversion

Answer 12

Divide into 2 isosceles triangles code-golf integer geometry

Given the measures of two of the interior angles of a triangle (x and y; the other angle can be easily calculated with 180 - x - y), draw a line segment that cuts this triangle into two isosceles triangles. You need to output the angle measures of both of your triangles.

However, because the base angles are the same, you only need to output the list [apex angle, base angle] of the divided triangles for both of the isosceles triangles. You can output the divided triangles in any order.

An example

Say your input is 100, 60.

Let's take a look at the complete triangle first. The triangle looks approximately like this.

   100

60            20

Now we try to divide one of the angles such that two divided triangles are both isosceles triangles.

       100

(40,20)           20

Now our bottom triangle is an isosceles triangle, since both of the base angles
of the bottom triangle are 20. The angle measures of the bottom triangle
looks approximately like this.

       140
20             20

Now, is the top triangle an isosceles triangle?

    100
          40
40

It is an isosceles triangle, because two of the angle measures are 40.

Therefore, for [100, 60], you need to output [[100, 40], [140, 20]].

Example cases

[20, 40] -> [[140, 20], [120, 40]]
[45, 45] -> [[90, 45], [90, 45]]
[36, 72] -> [[72, 36], [36, 72]]
[108, 36] -> [[108, 36], [36, 72]]

Answer 13

King+queen vs king checkmate code-golf chess

You are given a chess position, represented either in FEN or as a two-dimensional diagram like this (the example test cases will be using the latter format):

...k....
........
...K....
.....Q..
........
........
........
........

In the examples, K represents the white king, Q represents the white queen, k represents the black king and . represents blank space. You may choose different consistent values instead of these characters. You may also input the diagram as a list of lists or in any other way that is allowed by default for two-dimensional arrays.

It is white's move. The position will always be reachable from the starting position by a sequence of valid moves.

You have to find the minimum number of moves White must do to checkmate Black, assuming perfect play by Black.

Test cases

Incomplete: too many test cases for 1 and no test cases for >1.

...k....
........
...K....
...Q....
........
........
........
........

Output: 1

k.......
........
..K.....
........
........
........
........
.Q......

Output: 1

k.......
..KQ....
........
........
........
........
........
........

Output: 1

Answer 14

Underfull \hbox (badness 10000)

Every TeX user has been warned many times that their hboxes are terribly underfull or overfull. So much badness! This challenge is to rate how badly underfull or overfull a line of text is for a simplified line wrapper.

Task

You're given a space-separated string or list of words. Output the minimal badness achievable for the first line.

The text needs to be wrapped on a line that's 10 characters wide, but it can only be split on spaces, no in the middle of words. Any letter that spills beyond the width counts for 1000 overfull badness each, and each leftover empty position at the end of the line counts for 1000 underfull badness.

Example

For input "Overfull hbox", we can keep the word "hbox" in the first line for 3000 overfull badness, or wrap it to the second line for 2000 underfull badness which is smaller, so the output is 2000.

0123456789

Overfull hbox
          ^^^
Overfull
hbox    ^^

Note that we don't care about badness of the second line.

Details

The input is a space-separated string or a list of words made of letters a-zA-Z. It won't have any words more than 10 letters long, or be more than 20 characters in total. It won't be empty or have any zero-length words.

Test cases

TODO

---

Sandbox: Is it OK to have a multiplier of 1000 for theme? Should the underfull and overfull badness penalties be different, like 1000 vs 2000?

Answer 15

Lucky dice rolls

code-golf

In pen and paper roleplaying games dice are used for various chance calculations. The usual way to describe a roll is \$n\textbf{d}k\$ where \$n\$ is the number of dice and \$k\$ is the number of faces on a die. For example \$3d6\$ means that you need to roll the classical 6-sided die 3 times (or roll 3 dice at the same time). Both \$n\$ and \$k\$ are positive integers.

Usually the values are then summed and they are used for various game mechanics like chance to hit something or damage calculations.

A lucky roll will mean that you have Fortuna's favor on your side (or against you). Luckiness is an integer number that increases (or decreases) the sum in the following way. The roll is modified to \${(n+|luck|)}\textbf{d}{k}\$ and the sum will be the \$n\$ best (or worst) values. Each die is fair, so they will have the same probability for the outcome of the possible values.

The \$luck\$ can be a negative number, in this case you need to get the \$n\$ worst values for the sum.

Input

The integer values for \$n,k,luck\$ in any way.

Output

The expected value for the sum of the (un)lucky roll. The expected value is \$\sum{x_{i} p_{i}}\$ where \$x_{i}\$ is the possible outcome of the sum and \$p_{i}\$ is the probability for \$x_{i}\$ occuring, and \$i\$ indexes all possible outcomes.

Examples

n,k,luck    expected value
1,6,0       3.5
2,6,0       7
2,6,-1      5.541666666666667
2,6,1       8.458333333333334
2,10,-1     8.525
2,10,1      13.475

Scoring

Shortest code in bytes wins.

Good luck! ;)

Answer 16

Iterate diagonally over nxn matrix

Given a matrix of size n, output the matrix into another matrix of size n such that:

• the outputted matrix, when traversed diagonally,will result in the original matrix.

For example, taking this 3x3 matrix, we arrive at our solution:

Which is checked by following the line beginning at 1:

Specifications:

• The matrix will always be square
• You must output a grid with the same size as you were given (e.g. Not as a triangle)
• Mark the end of each row with a delimiter such as \n or .

Examples:

Example 1

Input:

1 2 3
4 5 6
7 8 9

Output:

1 3 6
2 5 8
4 7 9

We can check the output by iterating over the array diagonally (follow the arrows for steps 1-5), which will give us the original matrix.

  ↗ ↗ ↗
1 ↗ ↗ ↗
2 ↗ ↗ ↗
3  4 5 

Example 2

Input:

a b c d
e f g h
i j k l
m n o p

Output:

a c f j
b e i m  
d h l o
g k n p

We can check this by iterating the array in steps 1-7 which outputs the given array.

  ↗ ↗ ↗ ↗
1 ↗ ↗ ↗ ↗
2 ↗ ↗ ↗ ↗
3 ↗ ↗ ↗ ↗
4  5 6 7

Hint:

Looking at the coordinates, we can see a pattern:

(0,0) -> (0, 1) -> (1, 0) -> (0, 2) -> (1, 1) -> (2, 0) -> (1, 2) -> (2, 1) -> (2,2)

Answer 17

I am surely the fastest!... asymptotically code-golf restricted-complexity math

Posted.

Answer 18

Posted.

Answer 19

Write an expect program

If you're not already familiar, expect is a Tcl extension that makes it easier to script interactions with programs. It allows you to spawn a process, send lines to it, and wait for expected output before continuing.

Challenge

The aim of this challenge is to write a very simple implementation of expect in as few bytes as possible (code golf). It should parse a script, with commands separated by newlines. Then it should use this script to interact with a program.

Here are the commands for this implementation:

• spawn <cmd>: spawn a process.
• write <line>: write a line into the process' input.
• expect <line>: expect a substring from the process' output. No timeout is necessary, if the line never appears it is OK for the program to hang.
• print <line>: print something to stdout.

You can assume that only one spawn will be found in the script, and that it will appear before any write or expect. If your language of choice doesn't have the ability to spawn processes, you can write a helper program in a different language that can pipe input and output through your main program. How you do this is left up to you.

Example script:

spawn /bin/bash
write whoami
expect root
write uname -a
expect Linux
print i am root on Linux

Output:

this is Linux

or

spawn /bin/bash
write uname -a
expect Windows
print this is Windows

(no output.)

Restrictions

In order to keep things fresh, the use of the standard expect utility or any libraries that emulate expect functionality (such as pexpect on Python or jest on Node) are not allowed. The idea is that the bulk of the functionality should be written in the program and not handled in a library.

Answer 20

Count faces in ASCII art code-golf ascii-art

Here's a 2x2 ASCII art face:

oo
__

Here's a 3x3 ASCII art face:

o o
   
___

Here's a 4x4 ASCII art face:

o  o
    
    
____

Your task is to count faces in an ASCII art.

Here's something closer to an actual specification.

The bottom of any face must be a contiguous horizontal row of underscores, such that cells to the right and to the left of it do not contain underscores. If the row is considered as the bottom row of an ASCII square, then that square forms a face if and only if its bottom row is all underscores, its upper left and upper right corners are os, and the rest is whitespace.

You may assume all lines in the input to be padded on the right with whitespace to an equal length. Faces cannot be smaller than 2x2.

[todo: more test cases]

o o
   oo
_____

Output: 0

Sandbox stuff

Is it clear what is considered a face and what is not?

Answer 21

The almost impossible chessboard puzzle code-golf puzzle-solver error-correction

Background

Prisoner 1 walks in, sees a chessboard (8x8) where each square has a coin on top, flipped either to heads or tails. The warden places the key under one of the squares, which prisoner 1 sees. Before prisoner 1 leaves, he must turn over one and only one coin. Prisoner 2 then walks in and is supposed to be able to figure out which squares the key is in just by looking at the arrangement of coins.

The prisoners are granted a reward if prisoner 2 correctly tells the location of the key.

Task

Write two program/functions:

• One for prisoner 1, which outputs the location of the coin to flip given the current board state and the location of the key
• One for prisoner 2, which outputs the location of the key given the board state after prisoner 1 doing the flip.

If both the solutions are function they may share code with an auxiliary function, though the solutions may not share any information.

Scoring

This is code-golf so shortest bytes wins

---

Heavily inspired by The almost impossible chessboard puzzle and The impossible chessboard puzzle

Sandbox

• Should I include the error-correction tag
• Any more tags I should add
• Is something not clear

Also pretty sure this will require a lot of rewording before it can be asked

Answer 22

Infinite Mirrors Quine

This challenge is to create a program that prints out code that prints the original. Basically, this program should take an input, check if it's A, and if so, run section A. Otherwise, if it's B, run section B. Finally, if it's neither, print nothing. Section A should print the code in section B, and section B should print the code in section A. Section A's code and section b's code should not be identical. Shortest code wins!

Answer 23

Continuous Everywhere, Differentiable Nowhere

Objective

Build the Weierstrass function \$f(x) = \sum_{n=0}^\infty a^n \cos(b^n n x)\$, where \$a \in (0,1)\$, \$b\$ is an odd positive integer, and \$ab > 1 + 1.5\pi\$.

What's the fuss?

The Weierstrass function is an example of a function that is continuous everywhere, but differentiable nowhere.

Format

Using floating-point number is permitted. Though it will be preferred to use a datatype that is able to represent arbitrary real numbers.

Rules

\$a\$ and \$b\$ are up to your choice, as long as they satisfy the conditions.

For every \$x \in \mathbb{R}\$, evaluation of \$f(x)\$ must halt.

Note

The fact that the function above is defined as an infinite series might seem to contradict the rule, but it actually doesn't. The Weierstrass function is computable, implying that it is possible to halt for every input. In particular, if it were to be implemented over floating-point numbers, it suffices to stop summing when the summand becomes denormal.

Answer 24

Answer 25

Ant Storage Labyrinth code-golf matrix array-manipulation grid

Description

Using a simplified model, the place where ants store their food can be thought of as an \$n\times n\$ matrix. Each entry of the matrix is an integer that encodes how full that specific spot is, according to the following correspondence:

• 0 denotes an empty spot (the ants can add two more units of food),
• 1 denotes a half-filled spot (the ants can add one more unit of food),
• 2 denotes a filled spot (no more food can be stored in there).

Imagine an ant carrying \$f\$ units of food, that enters the "storage room" at a specific position (row \$i\$, column \$j\$ of the matrix). The ant can move one unit left, right, up or down with each step, and it can drop \$2-q\$ units of food at each spot it walks over (where \$q\$ is the initial capacity of that spot – either 0, 1 or 2 as described above). Your task is to find the length of the shortest path the ant can choose in order to store all \$f\$ units of food.

Example

Let's say that the ant carries \$4\$ units and enters the following storage room (\$6\times 6\$ matrix) at position \$(3,3)\$ (1-indexed):

$$\left[\begin{matrix}0&2&2&2&2&2\\2&1&2&2&2&1\\1&2&\color{red}{1}&2&1&1\\2&1&2&2&2&2\\2&2&2&2&2&2\\1&2&2&1&2&2\\\end{matrix}\right]$$

It drops \$1\$ unit right where it starts (\$3\$ left), then it has four optimal choices:

• 3 moves to the right, and 1 up,

  $$\longrightarrow\left[\begin{matrix}0&2&2&2&2&2\\2&1&2&2&2&1\\1&2&\color{green}{2}&\color{red}{2}&1&1\\2&1&2&2&2&2\\2&2&2&2&2&2\\1&2&2&1&2&2\\\end{matrix}\right]\longrightarrow\left[\begin{matrix}0&2&2&2&2&2\\2&1&2&2&2&1\\1&2&\color{green}{2}&\color{green}{2}&\color{red}{1}&1\\2&1&2&2&2&2\\2&2&2&2&2&2\\1&2&2&1&2&2\\\end{matrix}\right]\longrightarrow\left[\begin{matrix}0&2&2&2&2&2\\2&1&2&2&2&1\\1&2&\color{green}{2}&\color{green}{2}&\color{green}{2}&\color{red}{1}\\2&1&2&2&2&2\\2&2&2&2&2&2\\1&2&2&1&2&2\\\end{matrix}\right]\\\longrightarrow\left[\begin{matrix}0&2&2&2&2&2\\2&1&2&2&2&\color{red}{1}\\1&2&\color{green}{2}&\color{green}{2}&\color{green}{2}&\color{green}{2}\\2&1&2&2&2&2\\2&2&2&2&2&2\\1&2&2&1&2&2\\\end{matrix}\right]\longrightarrow\left[\begin{matrix}0&2&2&2&2&2\\2&1&2&2&2&\color{green}{2}\\1&2&\color{green}{2}&\color{green}{2}&\color{green}{2}&\color{green}{2}\\2&1&2&2&2&2\\2&2&2&2&2&2\\1&2&2&1&2&2\\\end{matrix}\right]$$

• 2 moves to the left, and 2 up,

• 1 move up, 2 left, and one up,

• 1 move up, 1 left, 1 up, 1 left.

All of these require \$4\$ steps, so the final answer is \$\boxed{4}\$.

Test cases

In progress. I need help coming up with interesting test cases / maybe a verification program.

Answer 26

Error Once, Hello World Twice

Your task here is to write a Hello World program that, (no, this is not Do X Without Y!) contains two exact copies of the same string. to avoid trivial solutions like print "Hello World!"# your program must error out with only one copy.

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

Sandbox

• Wording?
• Tags?
• Length?
• Interesting enough to be posted?

Answer 27

Successive operator sequences code-golf math arithmetic

A successive operator sequence (made up terminology) is a sequence of the form \$a(n + 1) = a(n) \text{ op } n\$ where op cycles through a set of operators and \$a(n)\$ represents the \$n\$th term of the sequence.

For examples, if we set the operators to addition, multiplication and subtraction and \$a(1) = 1\$. then we will get the following sequence (which is also A047908):

a(1)                    = 1
a(2) = a(1) + 1 = 1 + 1 = 2
a(3) = a(2) * 2 = 2 * 2 = 4
a(4) = a(3) - 3 = 4 - 3 = 1
a(5) = a(4) + 4 = 1 + 4 = 5
a(6) = a(5) * 5 = 5 * 5 = 25

Task

Write a program/function to output the \$n\$th term of a successive operator sequence given its initial term and operators.

Operators your program/function must support:

• multiplication
• addition
• subtraction
• integer division (rounded towards negative infinity)

Input Format

The operators are inputted as a string or array of character where each character represents an operator, you may choose your own mapping of character to operator.

Scoring

This is code-golf so shortest bytes wins.

Testcases

# first term, operators, n  ->  nth term
0,   ["+", "-", "*", "/"], 6   ->  4
1,   ["+", "*", "-"],      1   ->  1
1,   ["+", "*", "-"],      3   ->  4
1,   ["+", "*", "-"],      10  ->  199
1,   ["*", "+", "-"],      7   ->  -1
50,  ["*", "+", "-"],      1   ->  50
50,  ["*", "+", "-"],      4   ->  49
-10, ["*", "/", "-"],      5   ->  -32
-10, ["*", "/", "-"],      3   ->  -5
1,   ["+", "+", "*"],      5   ->  16
2,   ["+", "*"],           5   ->  36
0,   ["+"],                3   ->  3

---

Inspired by the sequence A047908

Answer 28

CoGo Rally

There's a game called Robo Rally, in which players "program" their robots five moves ahead, then simultaneously perform the moves, one at a time. The robots move over a "factory floor" grid, with the aim being to reach certain points on the board, in sequence, before the other robots do the same.

Game Rules

For the purposes of this challenge, the rules will be simplified as follows:

• Each robot starts with 6 lives
• Each robot has a different, randomly assigned starting position (out of a fixed set of starting positions)
• The aim of the game is to reach all three checkpoints in the assigned order, before any other robot does the same.

Movement Options

Each turn, your robot can make any one of the following movements:

• Rotate Clockwise 90 degrees
• Rotate Counter-clockwise 90 degrees
• Rotate 180 degrees
• Move Forward One
• Move Forward Two
• Move Forward Three [can only be used once until the next checkpoint is met]
• Reverse One (and stay facing the same way)
• Stay Still and gain 1 life, up to the maximum of 6

Your moves are pre-programmed in blocks of five, so choose carefully! The board may well be in a very different state in five moves time to what you think it will be.

Additionally, each movement is assigned a priority from 1-100. When you choose your block of five movements (you may use each movement any number of times, except the "move forward three", to form your five total movements) and the order they will occur in, you are also given five random numbers 1-100 to assign - one to each movement. Higher numbers will take priority where movements would cause two robots to enter the same space, for example.

Board Items

The board contains the following items:

• Floor - the default tile on the board. No special effect.
• Walls - block a robot's path. If a robot moves forward or backward into a wall, it wastes that move (i.e. stays still, but doesn't gain a life). If the robot used "Move Forward Two", for example, it may be possible that the Robot can only move Forward One, and then stops infront of a wall, wasting the second part of the movement.
• Laser gun - fire in a straight line in a specific direction until they hit a wall or a robot. If a robot is ontop of a laser gun, it will be hit but the laser won't fire further. While moving forward two or three, a robot may pass over the path of a laser gun without being affected by it.
• Conveyor Belts - at the end of a turn (single movement option), a conveyor belt will move the robot one space in the direction the conveyor is pointing. Doesn't block lasers. Conveyor belts NEVER ROTATE ROBOTS, even if they move the robot in a different direction to the one it is facing. While moving forward two or three, a robot may move over a conveyor belt without being affected by it.
• Checkpoints (1,2,3) - act as a save point on the Robot's path and also heals all of a robot's lives and resets their use of the "Move Forward Three" action, the first time the checkpoint is visited. Checkpoints must be visited sequentially to be activated. Acts as a piece of floor in all other respects. Robots must END THEIR TURN ON THE CHECKPOINT, after interaction with other Robots; and not just pass over it.
• Holes - move the robot back to the previously visited checkpoint, or start position. Robot loses half its remaining life, rounded down. Holes act immediately, as soon as the robot enters the space - it doesn't wait for the "board interactions" part of the turn order.

Interactions

Objects interact as follows:

• If a Robot moves into a space where another robot already exists, the other robot is shoved (moved) in the direction that the first robot was moving, one space; unless there is a wall or laser in the way. This effect may stack if multiple robots are in a line (i.e. all robots are shoved one space). This may cause a robot to fall into a hole or onto a conveyor belt.
• Moving off the edge of the board has the same effect as moving into a hole
• If a Laser fires and hits a robot, the robot stops the laser beam, and takes one damage.
• If a robot is facing another robot in a straight line with nothing blocking in between (i.e. no walls or other robots), the target robot takes 1 damage
  • Therefore If two robots are facing towards each other with nothing blocking in between (i.e. no walls or other robots), both robots take one damage.

Turn Order

1. determine (program) 5 movement options
2. determine Priorities (1-100) for these five turns
3. The programmed actions occur:
   a. The first movement occurs for each player, in priority order from highest to lowest. Holes are acted on immediately (a robot cannot pass over a hole).
   b. Robot Interactions are resolved (e.g. if one robot shoves another one)
   c. Board Items act (lasers, conveyor belts, checkpoints)
   i. If a robot loses all of its lives, it returns to the previous checkpoint (or start) with half lives (rounded up) and must sit out the remainder of the round d. Robots fire
   i. If a robot loses all of its lives, it returns to the previous checkpoint (or start) with half lives (rounded up) and must sit out the remainder of the round e. Repeat for the remaining 4 movements
4. Repeat until one robot has reached all three checkpoints sequentially, or all robots have lost their lives

The Challenge

Your robot must take the board (as a 2D array), and a seed for the Random number generator; and play the game on the given board.

The board is guaranteed to be solveable (there will always be a path from the start to each of the checkpoints)

Sample Board

The above board would be represented in an array as follows:

[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,LU,0,0,0,0,0]
[0,0,0,0,0,LL,2,LR,0,0,W,0]
[H,CL,CL,CL,CL,CL,CL,CL,CL,CL,0,0]
[0,0,0,0,0,CR,CR,CR,CR,CR,CR,H]
[0,W,0,0,0,0,0 ,0,0,0,0,0]
[0,W,0,0,0,0,W,0,W,0,0,0]
[1,W,0,0,0,0,CR,CR,CD,0,W,3]
[0,W,CR,CR,CR,0,CU,H,CD,W,0,0]
[0,LL,CR,CR,CR,CR,CU,CU,CL,0,0,0]
[0,0,S,S,S,S,0,0,W,0,0,0]

Where

Cx = Conveyor (x=Up, Down, Left, Right)
Lx = Laser gun (x=Up, Down, Left, Right)
S = Start
1,2,3 = Checkpoints
W = Wall
H = Hole
0 = Floor

Sandbox Questions

Should this be code-golf, where you implement your robot in the least code possible; or king-of-the-hill, or something else? If KotH, I've never set one before so some advice would be appreciated!

Answer 29

Paper folding. Posted HERE

Answer 30

The Dungeon Number Sequence code-golfnumberbase-conversion

Introduction

The dungeon numbers are introduced by Numberphile, denoting a chain of base conversions. A dungeon number is denoted in the form $$a_{b_{c_{d_\cdots}}}$$ where all numbers involved are integers with at least two digits. When interpreting the values, each base conversion \$a_b\$ is treated as from base \$b\$ to base-10.

There are two types of dungeons, one starting from \$10\$ to \$n\$ from top to bottom, i.e. $$10_{11_{12_{\cdots_n}}}$$ increasing \$1\$ for each deeper layer, and one starting from \$n\$ to \$10\$ from top to bottom, i.e. $$n_{(n-1)_{(n-2)_{\cdots_{10}}}}$$ decreasing \$1\$ for each deeper layer. Each dungeon has two interpretations, top down, i.e. $$(((10_{11})_{12})_\cdots)_n$$, and bottom up, i.e. $$10_{(11_{(12_{(\cdots_n)})})}$$, producing 4 dungeon number sequences in total.

Example

Considering $$10_{(11_{(12_{13})})}$$. The conversion is bottom up. First \$12_{13}\$ is converted to \$15_{10}\$. Then \$11_{15}\$ is converted to \$16_{10}\$. Finally \$10_{16}\$ is converted to \$16_{10}\$, and this is the value for \$n=13\$.

Challenge

Write a program or function, given an integer \$n>=10\$ as input, output either the value of the dungeon number sequence at \$n\$, or the whole sequence from \$10\$ up to \$n\$ inclusive. You may choose any sequence from the 4 sequences, but you must state which you have chosen. You must not hardcode the values; your code must work theoretically for all integer \$n>=10\$.

Values

n                                  10  11  12  13  14  15  16  17   18   19    20
---------------------------------------------------------------------------------
Type 1 (((10_11)_12)_...)_n        10  11  13  16  20  30  48  76  132  420  1640
Type 2 10_(11_(12_(..._n)))        10  11  13  16  20  25  31  38   46   55    65
Type 3 (((n_(n-1))_(n-2))_...)_10  10  11  13  16  20  28  45  73  133  348  4943
Type 4 n_((n-1)_((n-2)_(..._10)))  10  11  13  16  20  25  31  38   46   55   110

Sample IO

• Type 1 (\$(((10_{11})_{12})_\cdots)_n\$)

  15 => 30
  20 => 1640
  25 => 19563802363305
  

• Type 2 (\$10_{(11_{(12_{(\cdots_n)})})}\$)

  15 => 25
  20 => 65
  25 => 943
  

• Type 3 (\$(((n_{(n-1)})_{(n-2)})_\cdots)_{10}\$)

  15 => 28
  20 => 4943
  25 => 1092759075796059
  

• Type 4 (\$n_{((n-1)_{((n-2)_{(\cdots_{10})})})}\$)

  15 => 25
  20 => 110
  25 => 3577
  

Winning Criteria

This is a code-golf challenge, so shortest code for each language wins. No default loopholes.