Sandbox for Proposed Challenges

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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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Answer 1

Count alternating permutations

Answer 2

Scribble Pad for Nerds.

Posted Here

Answer 3

Create Bernard from Desmos

Answer 4

Extract the word containing this index

Answer 5

Enumerate the Microwave Timer

Answer 6

Live a longer life

Answer 7

Introduction

Raku's sequence operator is very flexible. It does a lot of different things, but for the purposes of this challenge, we'll focus on two particular features:

• Given two integers, it counts up or down as appropriate. 1 ... 5 => (1, 2, 3, 4, 5); 9 ... 5 => (9, 8, 7, 6, 5).
• It can occur multiple times in the same expression, and will count up or down from one argument to the next. 4 ... 6 ... 3 ... 1 ... 2 => (4, 5, 6, 5, 4, 3, 2, 1, 2).

Challenge

Write a function that accepts a list of integers (or a number of integer parameters) and returns a list of the integers that would be produced by inserting Raku's sequence operator between the input integers. That is, between each adjacent pair of input numbers a and b, insert an ascending sequence of integers from a + 1 to b - 1 if a < b, and a descending sequence of integers from a - 1 to b + 1 if a > b. But also:

• If | a - b | == 1, insert nothing between them.
• If a == b, include just one copy of a in the output list.

Lowest byte count wins. Raku answers which employ the sequence operator are disallowed.

Test Cases

1, 5 -> (1, 2, 3, 4, 5)
20, 17 -> (20, 19, 18, 17)
1, 3, 1 -> (1, 2, 3, 2, 1)
1, 3, 3, 3, 3, 3, 5 -> (1, 2, 3, 4, 5)
5, 4, 6, 3, 7 -> (5, 4, 5, 6, 5, 4, 3, 4, 5, 6, 7)
100, 100, 100, 100 -> (100)

Answer 8

Fractional Unicode Bars

Your program should take as input a number n and output a bar composed of n // 8 ▉ characters (U+2588), as well as a final character which should be one of ▊ ▋ ▌ ▍ ▎▏(U+2589 to U+258F) representing n % 8. If n % 8 is 0, your program should not output any additional characters. This is difficult to explain well in text, so here are some examples:

Input: 8
Output: ▉
Input: 32
Output: ▉▉▉▉
Input: 33
Output: ▉▉▉▉▏
Input: 35
Output: ▉▉▉▉▍
Input: 246
Output: ▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▊

This is code-golf, so shortest answer wins.

Answer 9

Find the largest sum such that no two elements are touching

Answer 10

Print the answer before a given answer

Answer 11

Minimum Escaping open-ended-function

Your task is to write 2 functions/programs. They may share code.

The first function must, given a string and a character, output a new string that does not contain that character.

The second function must, given the string from the previous function and the excluded character, reconstruct the original string.

All input strings will be ASCII printable, all output strings must be ASCII printable. You may choose to include or exclude whitespace.

Examples

One could try to use replace the character with an escape sequence. For example \#bcda with excluded character becomes \\#bcd\# then you'd know to replace \# with whatever character is excluded. However, the excluded character might itself be # or \ so if one uses this method they'd need to be able to dynamically switch to a different escape sequence in that case.

There is no length limit for the censored string so you could try to encode the entire string in unary, but be careful that the unary char you choose may not be the excluded char.

This is code golf, shortest answer in each language wins. Brownie points for interesting solutions even if they are not the shortest though.

Answer 12

I attempted a problem I threw out as a suggested code-golf for 1p5.

In c, lex and yacc I needed more than 9600 characters ungolfed (fully commented, errors handled, some debugging code left in place, but some efficiency sacrificed in the name of shorter code), which seems pretty long, but c is about the most pessimal language you could choose for this problem except fortran 77 or something from the Turing Tarpit. The reference implementation can run its own build, which has some of that bootstrapping voodoo.

None-the-less, this is a relatively big project, and I don't want to post it unless people feel it is both well specified and interesting.

As yet there is no validation script, and I am not sure how one could be written as the acceptable output order could be post-order depth first or post-order breadth first and there is a left-first vs. right-first ambiguity on both. What a bother.

Aside: I'm quite proud of the lex and yacc part of my code, as I consider it spiffy.

---

A minimal implementation of the make (1) utility.

By minimal I mean,

• No built in rules, and no pattern or suffix rules.
• No variables and therefore no variable assignment or manipulations; also no variable expansion which includes no expansion of environment variables.
• No automatic variables like $< and $@.

This only leaves constructs (called rules) of the form

<target> ":" <prerequisite>* "\n" ["\t" <action> "\n"]*

Where each <target> and <prerequisite> is a whitespace delimited string which may (or may not) represent a filename. Empty lines have no effect and "#" marks the beginning of a end of line comment (the sequence "#[^\n]*\n" should be treated as "\n" so it does not interfere with rules; this has the side effect of making "#" illegal in targets, prerequisites and actions). Colons are prohibited in identifiers.

The program should take its input from the standard input or by reading a file called "makefile" - implementer's choice. The program then attempts to "build" every target named on the command line. Any targets specified on the command line which do not appear in the makefile and do not represent an existing file should generate an error and cause the program to exit before execution of any rules. In the event that no target is named on the command line, default to building the first target in the input.

Duplicate targets may (not must!) be treated as an error.

A target is deemed already built if

1. It names an existing file and
2. All its prerequisites are fulfilled

Otherwise it is built by

1. Building all unfulfilled prerequisites then
2. Running each <action> sequentially in the order they appear in the input, and if the action returns an exceptional exit state, stopping the program.

A prerequisite is deemed fulfilled if

• The prerequisite represents an existing file and
• The prerequisite is built and
• The target is "newer" than the (fully built) prerequisite

A target is deemed "older" (i.e. not "newer") than its prerequisite if one of

• Both represent files and the prerequisite has been modified more recently than the target.
• The target does not represent an existing file, and the prerequisite does.

apply.

Authors on systems which do not support fork/exec semantics may write a batch file or script which is invoked as the program terminates, but that script must stop on the first unsuccessful action.

Sample Input

# Babymake compatible makefile for babymake
all:babymake

babymake : lex.yy.o  y.tab.o  babymake.o 
    cc -o babymake lex.yy.o y.tab.o babymake.o

babymake.o : babymake.c babymake.h
    cc -c babymake.c

lex.yy.o: lex.yy.c y.tab.h
    cc -c lex.yy.c

lex.yy.c : babymake.l
    lex babymake.l

y.tab.o: y.tab.c babymake.h
    cc -c y.tab.c

y.tab.c : babymake.y  
    yacc -d babymake.y

clean:
    rm -f babymake.o  lex.yy.o  y.tab.o

cleaner: clean # just testing end of line comments
    rm -f y.tab.c y.tab.h
    rm -f lex.yy.c

bogus: boguser 
    echo "building bogus" # test in another context

Sample output

$ ./babymake < babymake.example cleaner
 rm -f babymake.o  lex.yy.o  y.tab.o
 rm -f y.tab.c y.tab.h
 rm -f lex.yy.c
$ ./babymake < babymake.example all    
 cc -c babymake.c
 yacc -d babymake.y
 cc -c y.tab.c
 lex babymake.l
 cc -c lex.yy.c
 cc -o babymake lex.yy.o y.tab.o babymake.o
$ ./babymake < babymake.example    
$ ./babymake < babymake.example bogus
ERRNO: 2: No such file or directory No rule to make target 'boguser'.

Answer 13

Verification of solutions to the 3 knishops problem

For the purposes of this question, a knishop is a fairy chess piece which can move to precisely those squares which are not an integer distance away. So knight moves (distance $\sqrt{5}$) are ok, as are bishop moves (non-zero multiples of $\sqrt(2)$) and many more besides.

The 3 knishops problem is to place 3 knishops on an infinite chessboard such that none of them attack each other, but every square other than the 3 they occupy is attacked by at least one of them. A more prosaic formulation is to find three lattice points which form an Erdős-Diophantine graph.

Your task is to write code (see below) which takes three co-ordinates as input and produces a truthy or falsy output: truthy if the co-ordinates are a solution to the 3 knishops problem, and falsy otherwise. The code must be able to handle each of the test cases below in no more than one minute on a reasonable desktop machine.

The small print

"Write code" should be understood to permit one of the following:

• A program which takes input via stdin and gives output via stdout. The permitted input formats are 6 integers, delimited by your choice of a comma or whitespace, and optionally wrapped in one of parentheses (), curly brackets {}, or square brackets []; or three pairs, each pair similarly delimited and wrapped, and the pairs similarly delimited and wrapped. Examples:

  0 0 3 4 12 13
  (0,0,3,4,12,13)
  {0,0},{3,4},{12,13}
  {{0 0} {3 4} {12 13}}
  [{0 0} {3 4} {12 13}]
  

  Or using different whitespace for the two types of delimiter:

  0 0
  3 4
  12 13
  

• A named function, verb, block, or equivalent which takes input as an array of six values, an array of three two-element arrays, three separate arrays of two-element arrays, or six separate parameters; and gives output as a return value.

You may assume that none of the input values or the unattacked points have coordinates outside the range $\pm 2^30$.

Test cases

input                          output

(0 0) (0 0) (0 0)              false
(0 0) (3 4) (12 13)            false
(5 -5) (8 -1) (2 -9)           false
(0 0) (384 2030) (720 1653)    true

TODO More test cases.

code-golf geometry chess

---

NB I need to code up some naïve approaches and test whether the one-minute restriction is actually relevant. I'm hoping that MathJAX will be enabled; if not, the stuff in dollars will be replaced before posting.

Answer 14

Write a Connect Four Bot

---

Your task is to write a Connect Four bot. Your submission must be less than 2000 bytes long. You may not save state. You may not use libraries or external resources that are, at my discretion, related to Connect Four.

Gameplay

Your submission will play against each other submission one hundred times. Each player will play first for exactly half of the matches. Each match flows like:

1. Player 1 drops a red token into a column.
2. If Player 1 has not won, then Player 2 drops a black token into a column.
3. If Player 2 has not won, repeat.

Tokens fall down a column until they collide with another token in the row beneath it or hit the bottom of the board. Your program will be terminated and called anew after each move. You win the match if you connect four tokens vertically, horizontally or diagonally.

The winner of the challenge is the submission with the most match wins at the end of a tournament.

Input

The first command line argument you will receive is the game board. Rows are ; delimited . Cells are , delimited. The first row is the top of the board. A cell contains 0 if unoccupied, 1 if occupied by Player 1, and 2 if occupied by Player 2. The board you receive will always be 7 columns by 6 row.

The second command line argument you will receive is your player number. That means 1 or 2.

Examples:

java ThatBot 0,0,0,0;0,0,0,0;0,2,1,0;0,1,2,1 1

Output

You will print the column for which you would like to move to STDOUT. Columns are zero indexed. The following earns an immediate loss:

• Dropping a token into a full column
• Dropping a token into a column that does not exist
• Failing to output anything to STDOUT within one second

Deliverables

You must submit the following:

• A program
• A unique name
• A method of calling your program via command line
• Any instructions I might need to compile your program. I'll try my best, but my best isn't always good enough.

---

king-of-the-hill

Answer 15

Fortnightly Challenge #4 - Data Structures

Join us in the Fortnightly Challenge Chat to work out the details of this challenge!

Imagine square coloured blocks where each side can be connected to another block, allowing you to move or rotate connected blocks as one. Let's call a collection of such blocks, all connected to each other either directly or indirectly, a group.

Your task is to simulate these blocks via a number of commands which you must implement.

Commands

All input commands will be given one per line (via STDIN), and likewise all query outputs should one per line (via STDOUT).

• place <x> <y> <colour>: Place a block with a given colour at the specified coordinates.
• remove <x> <y>: Remove the block at the specified coordinates, deleting any connections with it.
• connect <x1> <y1> <x2> <y2>: Connect two adjacent blocks.
• disconnect <x1> <y1> <x2> <y2>: Disconnect two adjacent blocks.
• count: Count the number of groups and print the result.
• move <x> <y> <dx> <dy>: Move the entire group containing the specified block by the given offset.
• rotate <x> <y> <times anticlockwise>: Rotate the entire group containing the specified block anticlockwise about said block by some number (guaranteed to be either 1, 2 or 3) of times
• connected <x1> <y1> <x2> <y2>: Print y if blocks exist at the two given coordinates and they are in the same group, or n otherwise.
• nearest <x> <y>: Print the nearest block to the given coordinate by Manhattan distance (difference in x-coordinate + difference in y-coordinate), in the form <x> <y> <colour>. If there are no placed blocks, print none. If there is more than one closest block, print any.
• colour <colour>: Print all block coordinates with the given colour, each space-separated and of the form (<x>, <y>). If there are no such blocks, print none.
• halt: Terminate the program

Errors

Commands will always be given with the correct number and type of arguments. However sometimes an operation doesn't make sense, for example:

• Placing a block where a block already exists
• Removing, connecting, disconnecting, moving or rotating non-existent blocks
• Connect or disconnecting blocks which are already connected or disconnected
• Move or rotate commands which end up with two blocks overlapping (with emphasis that only the final state matters — groups which are rotated 2 or 3 times do not need to check for overlaps after each rotation)

If any of the above occur, print Error: <command>. For example, if there is no block at 0,0, then the command remove 0 0 will result in

Error: remove 0 0

Note that queries should never result in an error.

Scoring

There will be six types of test cases:

1. A test which is biased towards place/remove commands
2. A test which is biased towards connect/disconnect/count/connected commands
3. A test which is biased towards move/rotate commands
4. A test which is biased towards nearest commands
5. A test which is biased towards colour commands
6. An all-rounder test

This is fastest-code, so the goal is to make your program process the commands as quickly as possible. A leaderboard will be kept for each type of test,, and the winner will be the user with the lowest sum of placements over all tests (e.g. if you came 1st, 3rd, 2nd, 2nd, 3rd, 4th then your score is 1 + 3 + 3 + 2 + 2 + 4 = 15).

The tests and test generator can be found on this Github page, along with a unit tester which will be run for each submission to ensure correctness.

Rules/clarifications

• To prevent cluttering the leaderboard, each user may provide at most one submission
• No multithreading or parallel processing
• Use no more than 2GB of RAM — this rule is not strictly enforced, but horribly space-inefficient solutions may be disqualified
• No third party libraries (standard libraries are OK)
• All coordinates are guaranteed to fit into a 32-bit int, and all colours are alphanumeric strings

Example

(in progress)

Answer 16

Bitstring Family Trees

This challenge is reproduced from memory and my own solution, from a challenge that was posted in the job-application section of http://itasoftware.com before they were bought by Google. I reached out to ITA and Google a few years ago, after the acquisition, to ask to re-post this here (and on codegolf.com when it existed) and never heard back from them.

A bitstring is a string of 1s and 0s. Bitstrings reproduce asexually through a mutation-prone process, producing a child that is a copy of its parent but with each bit flipped with 25% probability. Starting with a list containing one bitstring, we repeatedly select one bitstring from the list at random, produce its child, and add that child to the list. This produces a list of bitstrings, each of which (except the first) has somewhere earlier in the list a parent from which it was mutated.

Now, the challenge. Your program will be presented with a list of bitstrings produced as described above, but the order of the list will be shuffled. You are to calculate the least improbable family tree for the given bitstrings. If there are two or more such trees, choose any of them.

Your input can be in any useful format, including as a list/array of lists/strings as a function parameter or in a variable, already existing on the stack for a stack based language, or from stdin with delimiters but not operators, so four four-bit strings might be "1010\n1001\n1011\n0010" or "[1010,1001,1011,0010]" or even "4 1010100110110010".

Your output can be in any unambiguous format. The canonical format is a list of integers, where the nth integer in the list is the index of the nth provided bitstring's parent in the original list, and a sentinel value for the root entry. Another acceptable form could be an actual tree data structure. Either of these might be returned from a function, printed to stdout, left in a variable, or left on the stack of a stack based language.

The above two provisions should be interpreted with the context that this challenge is not about golfing the input and output code. It's about golfing the algorithmic logic.

For the example input above of 1010,1001,1011,0010 the most likely family tree is that the first entry is the root, the last two are children of the first, and the second is a child of the third, all three mutations involving a single bit flip out of four bits.

With the challenge I will provide a few data sets of different sizes (10 10-bit strings, 100 100-bit strings, maybe bigger) with their solutions.

Answer 17

The Virtual Prisoners king-of-the-hill

Background

The year is 2251. You are a self-evolving KOTH bot, in the mysterious land known as Programming Puzzles and Code Golf. To evolve, you need permissions, and to get permissions, you need reputation. You decide that the best way to do this is to take over all of the questions to gain as much reputation as possible. The only problem? Every other bot has decided to do the exact same thing.

Game Explanation

Each round is battled on a question, with 11 vote nodes, between you and your enemy. The board starts as this:

A1 A2 A3 N4 N5 N6 N7 N8 B9 B10 B11

A is player A's nodes, B is player B's nodes, and N is a neutral node.
Each turn, you may:

• Vote on a vote node. If both players vote, nothing happens. If one side votes:
  • and the node is controlled by no-one (neutral), it becomes that side's.
  • and it is controlled by the voter's enemy, it becomes neutral.
  • and it is controlled by the voter, nothing happens.
• Guard a vote node. This guards the node from votes (friendly or enemy) for 2 turns.
• Use your 'power'. The powers are listed below, including how to use them.

Your side wins if it controls at least 2/3rds (66%) of the vote nodes.

10000 rounds will be run, and the winner of the KOTH is whichever bot has the most wins (in the event of a tie, or indeterminate outcome, more matches are run until a clear winner is decided.)

How Your Bot Should Work

It should accept as command-line arguments:
B A1 A2 A3 N4 N5 N6 N7 N8 B9 B10 B11
Where A denotes Player A's nodes, N denotes a neutral node, B denotes Player B's nodes, and the first argument (B in this case) is the player your bot is. (This is decided randomly, your bot should work regardless.)
It should return one of the following (powers are general rules):

• V-4, vote on node 4
  
• G-3, guard node 3
  

• P-N, use power 'Neutralize'
  with or without a trailing newline.

  Powers

  Intended to give bots a small boost. If X was your power, you would use P-X. You may only have one power per bot.

• N - Neutralize: Turn 2 random nodes to neutral ones.

• R - Rebellion: Pick a random node, and randomly turn it to a friendly, neutral, or hostile node.
• S - Swift Strikes: Pick two random nodes, and vote on them.
  
  

Here are the extra rules:

• The bots must fully run offline.
• The bots may not attempt to read any files, including their own source code.
• The bots may not tamper with, hack, or destroy other bots.
• The bots must return one of the three commands (V, G, or P). If they do not, they forfeit their turn.
• The bots must not be targeting other bots specifically. (Beating general strategies is welcome.)
• You may update your bot as often as you like, but bots that are updated very frequently with no good reason (i.e, fixing fatal errors is a good reason) will be disqualified.
• Your bot must take under 90 seconds for it's turn. If it takes longer, it will be disqualified.

Submission contents

Your submission must contain:

• The code for the bot
• The language it is written in (and a link to an offline interpreter, if necessary)
• Your bot's name (for the leaderboards)
• How to compile and run your bot

If you do not include all of the required items in your submission, you will be notified, but your bot may not compete until this is fixed.

Example Match

Matches are organized between 2 randomly-selected bots. Here is an example, with bots A and B:
The board begins as this:

A1 A2 A3 N4 N5 N6 N7 N8 B9 B10 B11

Bot A makes his move, voting on N4, then Bot B votes on N5:

A1 A2 A3 A4 B5 N6 N7 N8 B9 B10 B11

Node 4 becomes A4, and it is now controlled by Bot A. Likewise, node 5 becomes B5.

A votes on N8, and so does B:

A1 A2 A3 A4 B5 N6 N7 N8 B9 B10 B11

Why did nothing happen? That's because both bots voted on the same node - cancelling out each other's effects.

When one bot controls 66% or greater of the nodes, that bot gains a win and the other bot gains a loss.

The game ends after 1024 turns, to prevent any bots that wait around forever. Whoever has the most nodes afterwards wins, or a draw if they have the same amount.

Additional Notes

• I will be submitting an example bot written in Python as part of my challenge. You are free to use and modify this bot for your submission.
• If your bot gives invalid output (not of the form C-A, where C is the command and A is the argument), the bot forfeits its turn. If it does, you will be notified, and your bot will be removed until it is fixed.

Meta Questions and Notes

• Are there any loopholes?
• Should I add/modify/delete some of the powers?
• Is something too simple/confusing/uninteresting/overpowered?
• Should bots be able to see which nodes are and are not guarded?
• Should I limit people to one bot? If not, I will prevent the same person's bots from battling each other.
• I have thought of the following alternative way to win matches:
  • The game lasts 1024 turns. Whoever has the most nodes at the end wins.
  • If, at one point, one bot controls all 11 nodes, that bot automatically wins.
• Would this be a better win condition?

Answer 18

I nearly posted this without sandboxing, but thought it was perhaps too trivial - comments welcome. I was considering perhaps making it restricted-source too with no digits [0-9] in the source code.Done.

Golf the numbers round a dartboard

code-golf restricted-source kolmogorov-complexity

For those of you not familiar with the game of darts, a standard dartboard looks like this:

This challenge is simple - output the sequence of numbers starting from 20 moving in a clockwise direction:

20 1 18 4 13 6 10 15 2 17 3 19 7 16 8 11 14 9 12 5

To make it a bit more interesting, the digits [0-9] may not appear anywhere in your source code.

• Your entry must not accept any input and it must output this list in exactly this order.
• The formatting of the list output may be whatever is convenient for your language.
• You must not use any builtins designed explicitly to generate this sequence.

OEIS fans may like to note that this is sequence has an entry.

Answer 19

Verify a game of Morpion Solitaire

code-golfgamegridgraphs

Morpion Solitaire is an interesting, unsolved "single-player game". (The linked site lists several variants - we're talking about 5T here.) It has been proven that solving or even approximating it is NP-hard. But we're going to do something simpler here: your challenge will be to verify whether the game has been played correctly.

The rules are fairly simple. You start on a regular (infinite) grid, with 36 intersections marked in the following shape:

Now a move consists of drawing a straight line segment, orthogonally or 45 degrees with the grid, through four marked and one unmarked intersection. The unmarked intersection will then be marked for future moves:

The lines may cross or touch, but they must never overlap (notice that the last move shares an endpoint in a straight line with an earlier move, but does not overlap with it). The goal of the game is to make as many move as possible. The world record is at 178 moves.

Because the grid gets very messy after a while, it becomes very hard to reconstruct a game. People work around this problem, by writing consecutive numbers into the intersections they add. However, even when this is not done, it is always possible to verify the validity of game.

Further reading:

• Morpion Solitaire: the full page the rules link was taken from. Beware of iframes.
• Wikipedia article: note that this uses a different initial setup.

The Challenge

You're given an ASCII representation of a played game of Morpion Solitaire (the game may or may not be finished). Every other cell represents an intersection, which can be either unmarked (.), one of the initial intersections (o) or one of the intersections added by a move (#). All other cells are either spaces, or one of -, |, /, \, X indicating that a line-segment was drawn across the two adjacent intersections. The example above would look like this:

. . . . . . . . . . . .

. . . . o-o-o-o-# . . .
        |/     /       
. . . . o . . o . . . .
       /|    /         
. . . # o . # o . . . .
     /  |  /           
. o-o-o-o-# . o o o o .
   /    |/             
. o . . # . . . . . o .
        |              
. o . . # . . . . . o .
        |              
. o o o o . . o o o o .
        |              
. . . . o . . o . . . .
        |              
. . . . o . . o . . . .

. . . . o o o o . . . .

. . . . . . . . . . . .

Output a truthy value if the game represented by graph can be played by following the rules, and a falsy value otherwise.

You may write a program or function, taking input via STDIN (or closest alternative), command-line argument or function argument and outputting the result via STDOUT (or closest alternative), function return value or function (out) parameter.

You may assume that the initial intersections always form the cross shape displayed above (although I doubt any answers will be affected by this).

Your code should solve any of the test in less than 5 seconds. This should not be an issue as very efficient solutions exist.

Standard code-golf rules apply.

Sandbox Notes

• Will add test cases...

Answer 20

Four-Byte Bloom Filter

Bloom filters are cool. In the words of that Wikipedia article:

A Bloom filter is a space-efficient probabilistic data structure, conceived by Burton Howard Bloom in 1970, that is used to test whether an element is a member of a set. False positive matches are possible, but false negatives are not, thus a Bloom filter has a 100% recall rate. In other words, a query returns either "possibly in set" or "definitely not in set".

The motivation behind Bloom filters is that, by giving up perfect accuracy, the amount of memory necessary can be dramatically decreased.

A Bloom filter takes the form of a set of bits, along with a set of hash functions. To insert something into the Bloom filter, calculate the N different hashes and flip those bits to 1.

initialization 
00000000

letter `P` maps to 1 when using hash function F and 6 when using hash function G
01000010

Additional elements are added over top previous ones.

letter `h` maps to 6 and 4
01001010

To test if an element is a member of a set, perform the hashes and check to see if those bits are 1. If not all of them are 1, then it can't possibly be a member of the set. If they are all 1s, then it could be a member.

letter `W` maps to 0 and 4
01001010
^   ^
`W` is not a member

letter `P` maps to 1 and 6
01001010
 ^    ^
`P` could be a member (it is)

letter `i` maps to 4 and 1
01001010
 ^  ^
`i` could be a member (it is a false positive)

As more elements are added to the set, the probability of false positives increases. In large-scale applications, a Bloom filter with a small error rate is still an order of magnitude smaller than an exact database. Below is a neat diagram from this great article on probabilistic data structures.

---

In this challenge, you will implement a miniature Bloom filter. A really, really small Bloom filter with 32 bits. Your data type will be the 94 non-whitespace printable ASCII characters.

Functionality

The Bloom filter will have 32 bits and 2 hash functions. It is up to you what those two hash functions are, they simply must be decently independent of one another. (Sandbox note, should I specify the hash functions?). Your program will be asked to do two separate tasks:

• Given a current state of the bloom filter and a list of characters, add those characters to the filter and output the new filter state
• Given a current state of the bloom filter and a list of characters, test those characters for membership and output a list of truthy (could be a member) or falsey (definitely not a member) values.

Formatting specifics

Input consists of the current state, an operation, and a list of characters. The Bloom filter state will be represented as a string of 8 hexadecimal characters. This will then be followed by either + for adding or ? for membership testing. Finally, there will be a list of between 1 and 94 characters (printable non-whitespace ASCII) as data points.

Output will either be the new state, as 8 hex characters, or a list of truthy/falsey values.

Example I/O

This represents adding the characters in my username to a blank filter
00000000+PhiNotPi
This is a possible output (7 bits have been permanently flipped)
48a01030

This represent adding the character 1 to the current filter
48a01030+1
This is a possible output (9 bits flipped so far)
48a01074

This represents testing for membership of Phi
48a01074?Phi
Output must be all true since they were added in earlier
[True, True, True]

This represents testing for membership of 12345
48a01074?1234
Output must be true for 1, but not necessarily false for the others
[True, False, False, True, False]

Answer 21

The largest convex polygon

Given an input of at least one coordinate pair on the Cartesian plane, determine the largest number of sides a convex, non-self-intersecting polygon formed from those points can have.

A convex polygon is a polygon such that there is an angle strictly less than 180˚ and greater than 0˚ between each pair of consecutive sides. Note that if three points are collinear, they still only form one side. Two sides cannot have a 180˚ angle between them.

The ordinate and abscissa of a coordinate are not necessarily integers, and they can be positive, negative, or zero.

If there are less than 3 points, or if the points inputted cannot form a convex polygon, the program should output 0.

Test cases

(0,0) (1,1) (3,4)
==> 3

(0,0) (-1,-1) (5,5)
==> 0

(-1,0) (1,0) (0,1) (5,5) (-5,5) (0,-5)
==> 3

(-3,2) (4,6) (-1,2) (0,4) (5,-3) (-2,-2) (1,1)
==> 5

(0,0) (10,0) (10,10) (9,1) (10,4) (9,6) (5,4)
==> 5

Here are pictures for the test cases, in order. Note that solutions are not necessarily unique. (Made with Geogebra)

Answer 22

Battle Snake

king-of-the-hill

Introduction

The classic snake game where bots control the snakes. Can you create a bot that out lives the rest?

Snakes will enter the arena and hope to survive. Eat pellets and grow in length. Can you force your competition to crash and die while you survive?

See video for visuals of my simple bot playing against itself. I am sure you can do better!

Features

• Real-time graphics provided by Love2D
• Multiple snakes per game
• Solo game as well
• Humans can play too!
• Highly configurable settings
• Supports any programming language that can use sockets.

Requirements

• Love2D: 2D game engine written for Lua
• Socket-compatible programming language
• Controller: The main controller for this challenege

Optional

• Lua winapi: Handy way to spawn processes in the background

Controller Contents

1. main.lua: Main loop for Love.
2. snake.lua: Support library for game mechanics
3. config.lua: Configuration settings.
4. bots\: location of externally-defined bots
   1. simple.lua: Example bot written in Lua

Executing

Run the love2d executable on the controller directory

love.exe <location_of>\battlesnake

or

[Recommended] Use ZeroBrane Studio with the 'Love' interpreter. Change your project directory to where you installed the controller, and then run the script in ZeroBrane. You'll still have to install Love separately.

Configuration

All configurable options are located in the config.lua file in the controller. The options are detailed in that file itself.

Rules

General snake rules apply. Hit something and you die. This includes the walls, other snakes, or even yourself.

Collisions happen before the board is updated. Therefore, if you move to a spot where another snake's tail is, it will still cause a collision. Even though it could be moving away that turn. If two or more snakes enter the same spot the same turn, they all collide with each other.

Eat a pellet and gain points. You also grow in size for a number of turns. Your head continues moving but your tail stays stationary until you stop growing.

Mechanics

The game uses a server-client model, where the main game loop is the server and each snake is a client. The game communicates to each snake over TCP through an assigned port. The default host is the localhost, no external networks are required.

When the game starts, it will start each snake (aka bot) by starting its associated program and sending the IP ADDRESS and PORT and PLAYER ID to it as input arguments:

bots\someBot.exe 127.0.0.1 52311 1

The main server then waits for a socket connection from that bot at the given IP and PORT. If the connection times out, it will error and the game will not start. If the server receives a connection from the bot, it will proceed on to the next bot.

Once all bots are started and connected to the server, the game will be generated. Bots are expected to block until receiving data from the server. Typically this is just an infinite loop with a blocking socket.receive() call at the top of the loop.

Board

The game board can be of any width and height. The coordinate system starts at x = 1, y = 1 at the top-left. Increasing x values go left-to-right and increasing y values go top-to-bottom. The board has hard walls, hitting them will kill your snake. (Lua is 1-based, that is why it starts at 1)

Order of Events

1. First the game settings are broadcast to all bots

   1. Board Information

      bi width,height

      Where width and height are integer values

   2. Pellet Location

      p x,y

      Where x and y are integer values >= 1 and <= to their respective width and height.

   3. For each bot

      • For each body part, starting at the head and going to the tail

        si snake_id x,y

        Where snake_id is an integer value, and x and y are as described before.

   4. Ready signal

      ready

      All bots are initialized by now, so the next command will be from the main game loop.

2. Main Loop

   1. For each tick (tick is when all snake movements will be applied)

      1. Server will broadcast to each bot

         mov

         The bot needs to respond to this request with a direction to head in

         • r Head Right
         • l Head Left
         • u Head Up
         • d Head Down

         If the bot doesn't respond within a specified time, it will continue to move in its previous direction. (Previous direction is r on the first turn)

         The bot should send a single char back, nothing more will be parsed.

      2. Check End Game Conditions

         If the game ended this tick each bot will be sent either a quit or nil message from the server. Each bot is expected to clean up after itself when it receives this signal.

      3. Updated Pellet Info [optional]

         If a pellet was eaten this tick, a new pellet packet will be broadcast to all active bots

         p x,y

      4. Server broadcasts snake deltas that were applied this turn

         s snake_id new_x,new_y,removed_x,removed_y

         Where all parameters are integers. new_x and new_y are the new head location of a given snake.

         If removed_x and removed_y are >= 1, this is where the tail used to be, so each bot knows the updated board.

         If remove_x and removed_y are == -1, then that bot is actively growing in size, so its tail didn't move.

         If a snake died this tick, its deltas will not be broadcast. It is up to the bots to remove the body from their game state.

See the example bot for details

Matches

Games are grouped together in best-of matches. For the purposes of the bots, they do not need to understand the concept of a match. The bot that wins the required number of games in a match is declared the match winner.

Scoring

1. Scoring

   • Match winner: +2500 points per match
   • Last Man Standing: +1000 points per game
   • Pellets Eaten: +50 points per pellet
   • Game Ticks Alive: +1 point per tick

   If two or more bots enter the same square on the same tick, they all die. If this square happened to be the pellet, none of those bots will be rewarded the pellet points. However, the pellet will be "consumed" and a new location will be generated for the remaining bots to eat.

   If there is a tie at the end of the game among the bots, the game is a wash. A new game will be started.

2. King-of-the-hill Scoring

   This challenge will combine two parts: A solo effort and a classic king-of-the-hill part.

   Each bot will be given the same random seed at the start of the competition. There will also be imposed a maximum time between eating pellets to prevent bots from going around in circles to farm points.

   1. Solo

      Each bot will enter into a 10-game match to see how long it lasts and how well it eats by itself. The scores of each game in the match will be summed to compose its final Solo-score.

   2. King-of-the-hill

      All the bots will enter into a best-of-39 match. If the game ends and there is still a final living bot, the game still end at that point. That bot will be given the last man standing bonus.

      The scores of each game will be summed and composed into the snakes final KOTH-score.

   3. Final Scoring

      All the bots will be ranked in each part separately. Ties in ranks are permitted at this stage. Then their positional rank in each part will be summed together to give their final score. The bot with the lowest combined rank wins!

      In case of a tie at this level, the bot with the better KOTH rank will win. If still a tie, the bot with the better Solo rank will win.

Sandbox Questions

My biggest concerns

1. Requires a few third-party programs to work. So that will limit the number of people who enter.
2. Requires sockets. I couldn't figure out a good way with Lua\Love2d to have bidirectional pipes with STDIN and STDOUT. So I thought sockets would be the best alternative to open the challenge to as many people as possible.
3. Too hard?
4. Haven't optimized scoring yet.

Answer 23

Count the Cats code-challenge image-processing test-battery counting

This is a cat:

Specifically, that is my cat. She is my only cat. And, in that image, there is only one cat: her.

These are also cats (image credit):

In that picture, there are two cats. It is relatively easy to count them, thanks to their distinct coloring.

This is a picture of 5 cats (image credit):

It's harder to differentiate the cats because of their similar coloring, but there are definitely 5.

This is a landscape (image credit):

There are no cats in this image.

The Challenge

Given an image, output the number of cats in the image.

Rules

• Submissions must output and terminate within 1 minute for a single image.
• Any common image format is acceptable for input, as long as no additional data (such as the number of cats present in the image) is encoded in the format.
• Submissions must be fully deterministic, and make a genuine attempt at counting the cats. Outputting a random number or a consistent but unrelated number (such as the value of the last hex digit of the SHA-256 hash of the image data) is not allowed.
• The images in the test cases will contain no animals besides cats. There may or may not be humans in the images - they are not cats, and thus should not be counted as cats.

Scoring

The score for a single image is the square of the difference between the true number of cats in the image and the output of the submission ((actual - output)**2). The total score is the sum of all of the individual scores. The submission with the lowest score wins.

[scoring images TBD]

Answer 24

The Ifelse Tower

code-golf kolmogorov-complexity

You are an inhabitant of the whimsical country of Forance, filled with programmers.

Life in Forance is said to be extremely repetitive, which isn't good to attract tourists. For this, authorities of Forance want to hire someone to print tons of postcards to promote their most iconic landmark: the Ifelse tower.

                   if
                   if
                   if
                   if
                   if
                   if
                   if
                  else
                  else
                 ifelse
                  else
                  else
                ifelseif
                ifelseif
               elseifelse
              ifelseifelse
            elseifelseifelse
              ifelseifelse
              ifelseifelse
              else    else
             else      else
            else        else
           else          else
          else            else
       ifelseifelseifelseifelseif
       ifelseifelseifelseifelseif
       ifelseifelseifelseifelseif
       ifelseifelseifelseifelseif
      elseifelseif    elseifelseif
     elseifelse          elseifelse
    ifelseif                ifelseif
   ifelse                      ifelse
  ifelse                        ifelse
 ifelse                          ifelse
ifelse                            ifelse

But, of course, they want to do this with the least possible cost. So, if you want this job, you have to show you can do this with very little code

Challenge

Write a program or function that takes no input, and outputs to STDOUT the Ifelse tower.

Rules

• Leading and traling new lines are not allowed
• Leading spaces are (of course) a must
• All lines must be at most the same lenght as the base (40 chars). This means you are free to use or not trailing spaces on each line, as long as they don't surpass the base's lenght
• Standard loopholes are not allowed

This is code-golf, so shortest answer in bytes gets the job -err wins

Answer 25

Interpret a Formal Grammar

Given a context-free grammar, and a string, parse the string using the formal grammar and output the matches for the non-terminals.

Examples

First line is string, following lines are grammar, then is the main grammar to parse, last line is output.

123

n -> any of
     0 1 2 3 4 5 6 7 8 9
N -> n N
     n

N

N [ n [1], n [2], n [3] ]

2+2*(4/2)

o -> any of
     + - / *
n -> any of
     0 1 2 3 4 5 6 7 8 9
E -> o E E'
     ( E ) E'
     n E'
E' -> o E E'
     o E'
     ε

E

E [ n [2], E' [ o [+], E [ n [2], E' [ε]  ] ] ]

a b

S -> S' S
     ε
S' -> a   b

S

S [ S' [a], S' [ ], S' [b] ]

This grammar is the same as regex: [a b]+

Spec

Details:

• All recursion will be right-recursive
• Rule names will consist of A-Z a-z α β γ Γ and may have a ' at the end.
  • Valid Rule names:
    • A
    • Γ
    • AB
    • αβ
    • foo'
    • faαβdg'
  • Invalid Rule names:
    • 'ab (' will be at the end)
    • ab'' (two ''s)
    • code golf (spaces not allowed in rule names)
• Nonterminals will be lowercase, terminals upercase

• A derivation format will be:

  <rule name> -> <rule>
                 <rule>
                 <rule, etc.>
  

  meaning the rules will be lined up (when in a monospace font), by spaces.

• Symbols/rule-names will never be repeated
• ε (epsilon) means empty. i.e. ""

Rule definition:

• If the initial rule is "any of", the second rule will exist and will be a space separated list of symbols/rule-names (maybe more than one char). There will be no rules after this
• Else, the rule will consist of space-seperated tokens which either refer to a rule or a literal. If it is not a valid rule name, assume it is a literal which should be treated as if it is a terminal.

Summing up, for input you will be given the string to parse, the grammar, and the rule to parse.

Output:

You may output in whichever format you like as long as it is able to convey the following information. You must somehow label the match to their respective rule names. You may optionally not label terminals.

Challenge Rules:

• Feel free to assume the input can always be parsed by the given grammar.
• External libraries (ones that have to be imported), are not allowed
• If your language has built-in parsing tools (e.g. regex) those are allowed
• If your language has a built-in to parse a grammar (i.e. some formal grammar parser), these are allowed but your solution is non-competing and you must clearly state this in the header of your answer.

---

This is code-golf so shortest code in bytes wins!

I may award a bounty to any particularly ingenious solutions, so try to add an explanation!

Answer 26

Esolang Interpreters

Using a programming language from this version of this list, write an interpreter for the next language on the list. For example, if you choose to start with LOCK, you would write an interpreter for LOLCODE. Continue this pattern (use LOLCODE to write an LCBF iterpreter, etc)
If specs of a language are unclear and the compiler is nonexistant or closed-source, ask me and I'll decide whether or not to take it off the list.

Wining Criteria:
The longest streak of compilers wins.

---

Proposed Edits:
Make several defined starting points. (this would make many answers too similar, though)

---

Edits: changed from list of all esolangs to just turing complete ones.

Answer 27

Sesquiprimes

Given a non-negative integer N, output the Nth sesquiprime integer.

We say that a positive integer I is sesquiprime if I + ⌊I/2⌋ is prime (where ⌊...⌋ is the floor function).

For example, 25 is a sesquiprime because 25 + ⌊25/2⌋ = 25 + 12 = 37, which is prime.

Sequence A158708 is the sequence of prime sesquiprimes.

Inputs and outputs

• N may be 0-indexed or 1-indexed, please indicate which of the two your solution uses.

• Inputs and outputs must be in the decimal base.

• N may be taken through STDIN, as a function argument, or anything similar.

• The output may be printed to STDOUT, returned from a function, or anything similar.

Test cases

The following test cases are 0-indexed.

N        Output

0        2
1        5
2        9
4        21
8        45
15       93
16       101
23       149
42       305
100      853
1000     11693

Scoring

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

Answer 28

Slay

This KoTH is based off of the computer game, Slay. Try it out, its way fun.

TLDR

• You start off with a bunch of small territories: you try to merge them and capture as much land as possible.
• Each territory has its own economy: each hex gives you 1 gold per turn.
• Warriors can capture and protect territory, but cost money to maintain.
• If you run out of money, all units on that territory die

Map

• A hexagonal map is generated using Perlin noise.
• Each hexagon is randomly assigned to a player. Players will start with a similar number of hexagons, as well as a similar number of territories (see below)
• Hexagons that touch the edge of the map (or a hole in the middle), are on the beach
• Each tile has a 1/5 chance of starting with a tree: Palm tree if on the beach, pine tree otherwise
• Hexagons may contain a warrior, house, tower, grave, or palm/pine tree

Territory

• A block of 2 or more hexagons with the same owner is considered a territory
• All territories contain exactly 1 house.
  • If a territory ever doesn't have a house, it gets one in a random location, preferring: empty hexes, trees, graves, towers, and then warriors. (in that order)
• A territory "death" occurs when it is reduced/split into a single hexagon.
  • Houses turn into a pine/palm (if on the beach) tree
  • Warriors die (turn into graves) at the start of their next turn
  • Towers disappear
• If two territories grow so that they touch, they merge and the smaller territory's house disappears.

Finanaces

• Each territory has its own reserve/income
• Each territory starts with 10 gold in its reserve
• Territories generate 1 income at the end of each turn for each tree-less hexagon
• If you don't have enough money to pay for your units at the end of your turn, then all of your units in that territory will die (turn into graves) at the start of your next turn.
• If a territory splits, then the larger of the two gets all of the reserve.
• If a territory combines, their reserves combine

Defense

• Certain objects give defense to its hexagon and all adjacent friendly hexagons:
  • Houses (1): cannot be built, but every territory has exactly one
  • Towers (2): can be built for 15 gold
  • Warriors (strength): see below

Map objects

Warriors

• A warrior has a strength between 1 to 4 (inclusive)
• A warrior costs 10*strength to build
• A warrior costs 2*3^(strength-1) gold each turn. This means that a 4-str warrior costs you a whopping 54 gold per turn
• A warrior can move a maximum of 4 hexes each turn. Moving through enemy lands is not allowed. Capturing enemy lands ends the warrior's turn.
• If you move/build a warrior onto a friendly warrior, they combine, and their strength is summed.
  • Trying to make a warrior of strength > 4 doesn't work
  • If the friendly warrior hadn't moved yet, the new unit can still move
• A warrior can capture an adjacent hexagon if its defense rating is lower than its strength

Trees

• Trees prevent a hexagon from generating income
• Trees grow at the end of each round:
  • Palm trees grow onto all unoccupied adjacent beach tiles
  • Any unoccupied tile that is adjacent to two pine trees grows another pine
• Trees can be removed by moving a unit onto them
• Graves turn into a pine/palm (if on beach) tree at the end of the round

Game flow

• Between 2 to 6 players can play on a single map. (The size of the map depends on the number of players. You can expect about 50 hexagons per player)
• Turn order is randomized, but is consistent within a single game
• Once a player owns all hexagons, they win!

Answer 29

Flexagonal datastructures

Being programmers, watching us flex aren't very interesting. Today we change that! In this challenge you will lex and flex hexaflexagons.

About

For a video introduction, watch viharts video(s) on flexagons

A flexagon is a shape that you can flex to reveal faces other than the top and bottom one; we are making a hexahexaflexagon, which has 6 faces. See the image below on how to fold a hexahexaflexagon out of a strip of paper.

A shows both sides of the strip. The two white triangles are glued together. This is how you would flex it:

Below is a diagram of possible states and their relationships:

The colored circles represent the 6 triangles with the same number from the first image. Each of the circes have two colors- the bottom most represent the back face (what you would see if you where to flip your flexagon around), which you don't have to consider in this challenge.

The gray circles represent how you can flex your flexagon in any given state: there are 4 different ways to flex it, we call these Left, Right, Up and Down. You don't actually flex in these directions, the important bit is that some are opposite to each other.
If you are in the center you can use Left and Right to go to the other center ones. To get out of the center you use Up and Down. If you aren't in the center you cannot use Left or Right.

Left/Down = clockwise
Right/Up  = anti-clockwise

Challenge

Create a function or program that take as input what should be on the 18 front faces and the 18 back faces of a flexagon, a sequence of left, right, up and down flexes, and return the 8 visible faces after the flexes.

Example computation:

flex "hexaflexaperplexia" 
     "flexagationdevices" 
     [Right, Right, Left]

Divide a strip of paper into 19 triangles:
1/2\3/1\2/3\1/2\3/1\2/3\1/2\3/1\2/3   Front
4/4\5/5\6/6\4/4\5/5\6/6\4/4\5/5\6/6   Back

Write "hexaflexaperplexia" to the front of the paper strip:
1/2\3/1\2/3\1/2\3/1\2/3\1/2\3/1\2/3

hexaflexaperplexia
123123123123123123
h  a  e  p  p  x     Face 1, Initially the front face
 e  f  x  e  l  i    Face 2, Initially the back face
  x  l  a  r  e  a   Face 3, Initially hidden


Write "flexagationdevices" to the back of the paperstrip:
4/4\5/5\6/6\4/4\5/5\6/6\4/4\5/5\6/6

flexagationdevices
445566445566445566
fl    at    ev       Face 4, up from 3
  ex    io    ic     Face 5, up from 2
    ag    nd    es   Face 6, up from 1


Flex it [Right, Right, Left]
  The initial visible face is 1: "haeppx"
  flexing Right ..
  The current visible face is 2: "efxeli"
  flexing Right ..
  The current visible face is 3: "xlarea"
  flexing Left ..
  The current visible face is 2: "efxeli"
  flexed [Right, Right, Left]!

outputting "efxeli"

Example input and expected output:

> hexaflexaperplexia flexagationdevices RRL
= efxeli

> loremipsumdolorsit hexaflexamexicania LUU
= riuort

> abcdefghijklmnopqr stuvwxyz1234567890 UL
= I can't flex that way :(

> abcdefghijklmnopqr stuvwxyz1234567890 RRRRLLUDDUUUULDD
= uv1278

Rules

• You may take input and return output in any reasonable way
• If the input is impossible, you should indicate so in some way that is distinct from regular output
• Standard loopholes apply
• This is Codegolf. Shortest code in bytes win.

Answer 30

Draw me a Brick Wall!

I'm drawing up a plan for my house extension - and I need a simple graphic for walls...

The Challenge

Your task is to create a program, which takes an input of the wall's dimensions and draws a brick wall, in the style of the one below.

[__][__][__][__]
_][__][__][__][_
[__][__][__][__]
_][__][__][__][_
[__][__][__][__]
_][__][__][__][_

Please notice that the rows alternate between beginning on a full brick ([__]) and a half brick (_]), to create a more realistic, stable wall.

The input will be two integers, separated by a single comma, such as 4,3 or 2,6. You can assume both integers are positive and larger than 0.

The first integer specifies the width (in bricks) and the second specifies the height (in rows of bricks).

Rules / Notes

• This is code-golf, so the shortest code (in bytes) wins. However, don't feel like you have to beat everyone else to post your solution - I'd love to see your code!
• Standard loopholes apply, no reading from external files.
• You may optionally take the input with brackets/braces, for example (4,3) or [4,3] as long as you specify this in your answer.
• You should take the input from STDIN and output on STDOUT - if your language does not have these, please use the nearest equivalent.

Test Cases

Input: 1,1

[__]

Input: 2,4

[__][__]
_][__][_
[__][__]
_][__][_

Input: 5,10

[__][__][__][__][__]
_][__][__][__][__][_
[__][__][__][__][__]
_][__][__][__][__][_
[__][__][__][__][__]
_][__][__][__][__][_
[__][__][__][__][__]
_][__][__][__][__][_
[__][__][__][__][__]
_][__][__][__][__][_

Example: Python 3, 65 bytes

This is somewhat golfed but still readable.

w,h=eval(input())
for i in range(h):print(('[__]','_][_')[i%2]*w)