Sandbox for Proposed Challenges

Question

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

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• Parts of the challenge you found unclear
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Answer 1

Render STL files

code-golfgraphical-output

STL means StereoLithography. It's a common file format, used in 3D printing.

The way it works is quite simple. You change every surfaces to triangles. For example, a cube would have 12 triangles, since it has 6 sides, and each sides has 2 triangles.

In this challenge, you have to read STL(A) files and render them.

---

Explain me more about the file format..

^{Well, technically, I linked you to the wikipedia, but I'll just explain, You can just, uh, go to the wiki if you want, you know?}

Alright. the file is in this format.

solid [optional name]
facet normal ni nj nk
    outer loop
        vertex v1x v1y v1z
        vertex v2x v2y v2z
        vertex v3x v3y v3z
    endloop
endfacet
endsolid [optional name]

The part you have to look is the vertexes. you can see there are 3 vertexes each with three numbers (each of them are coodrinates of each axes). Remember I told that you change every surface to triangles? These three vertexes form a triangle.

and the part between facet normal and endfacet will be given multiple times, forming multiple triangles, forming a 3D object. like the cube I told you before.

You do not have to look at the numbers right after the facet normal. it will not affect the shape. (at least in this challenge)

---

Examples

I couldn't copy all of them so I decided to leave a link.

Answer 2

Sandbox notes

• This is the first time I write a controller; and it's been a while since I wrote an actual program. If you feel so inclined, feedback is appreciated.

Initial draft of the controller (java) here: https://github.com/S119349/cooperative-koth

---

king-of-the-hill The Cooperation Game

king-of-the-hill card-game java

In this king-of-the-hill challenge, instead of competing, players will have to work together to beat a game. The player who on average gets the best results over all game runs, is the winner for this challenge. The game is inspired on the mechanics of "The Game".

Game mechanics

The goal of the game is to play as much cards as possible on four piles on the table. Two piles can only accept cards in strictly increasing order, the other two in strictly decreasing order. The game is over as soon as a player cannot play a card.

Piles

The game starts with four piles, numbered 0 through 3 inclusive. Piles 0 and 1 accept cards in strictly increasing order; piles 2 and 3 accept cards in strictly decreasing order. Initially, the piles are

Pile number |  0  |  1  |  2  |  3  |
       Card |  1  |  1  | 100 | 100 |

There is an exception to the rule of accepting only strictly increasing/decreasing order. You are allowed to play a card exactly 10 less or more respectively than the current card. For example, if the piles are

Pile number |  0  |  1  |  2  |  3  |
       Card |  1  |  32 |  78 | 100 |

you are allowed to play 22 on pile 1, or 88 on pile 2.

Taking turns

The game starts with a shuffled draw stack containing 98 cards, numbered 2 through 99 inclusively. Each player is dealt 6 cards at the start of the game. The cards are known only to the players themselves.

During a turn, a player must play at least two cards ^{Exception: you only have one card, or you're out of cards, because the draw stack is empty}, up to all the cards in their hand. After their turn, the player will restock from the draw stack to 6 cards (or less at the end of the game).

Reacting

After each card is played, other players are allowed to react: if you have the perfect card in your hand, you may want to warn players not to add anything to that pile! Since your cards are secret to you, this is done by assigning priorities to each pile. The priority is from 0 to 5 inclusive, with 0 signifying no interest at all in that particular pile, and 5 begging other players not to add anything to that pile. Other players can use these priorities as they deem fit; including completely ignoring it.

Interaction with the controller

You will create a player that extends the abstract Player class. You will have to implement void turn() (for playing a card) and int[] react() (for announcing your priorities). A reference implementation, SimpleTom, is provided, but may be removed from the competition if there are enough competitors.

In void turn(), you are required to either playCard(int card, int pile) or endTurn(). Note that you may only play one card per invocation of turn(), to give other players an opportunity to react(). Doing anything else (playing two cards, playing no cards at all) will result in losing the game, with all the cards still in the game adding towards each player's score!

In int[] react(), you are required to return an array of your priorities on each pile. An example would be return new int[] {a, b, c, d} with a through d the priorities for each pile. Here, 0 <= a <= 5.

To see what is happening, you have access to some members

• ArrayList<Integer> hand contains all cards currently in your hand.
• In the gameState member of the default Player class:
  • int [] gameState.piles contains the four piles. It is an integer array of size 4, with each element the last played card on that pile.
  • Map<Player, int[]> gameState.priorities. A map containing the latest priorities issued by each Player in the game.
  • Player[] gqameState.players can be used to list all the players in the current game; as well as determine how many cards they have by calling int nHandCards(). Note however that you may not access these players in any other way! (force them to do a turn, force them to lose, make them expose their hand, etc).

Concerning the other players: you may know who is playing and assess their skill during a game (for example, figure halfway through a game that SimpleTom is not trustworthy, and that two of the other players are of type SimpleTom). You may not save this information between games, or hard-code strategies concerning other players.

Do's and don'ts

All entries are open-source. You are encouraged to write commonly used functions (e.g., something to keep track of what cards have already been played) as separate functions, so others may use them. When you use code from others, always attribute your source. It is not OK to copy someone's algorithm and just tweak a few values - your code should be significantly different from others.

You are allowed to use a different languages than Java, if you write your own wrapper class (or use someone else's wrapper class). I usually only use Try it Online!, so I don't have any compilers installed on my Ubuntu box. If you use another language that is not available on Ubuntu by default, please include a few lines on how to install your language. Your entry will be non-competing if it takes me more than two minutes to follow these instructions, so a script or copy-pasteable command line code is preferred.

Answer 3

Hex address to little endian escaped string

You are a brilliant hacker and you just gained access to a unprotected computer! To complete your exploitation, you need to convert a set of hexadecimal addresses into a different format.

You remember your lessons from university and you find out the machine you're on is little endian, meaning the order of the bytes is "reversed".

To make a break from your illegal activity, you decide to code a little program that does that automatically.

The Goal

Convert a string of the form

0x12345678

to

\x78\x56\x34\x12

You set up a few tests and their potential results:

0x080483b4   =>   \xb4\x83\x04\x08
0x00000fff   =>   \xff\x0f\x00\x00
0xfffffff0   =>   \xf0\xff\xff\xff
0xefbeadde   =>   \xde\xad\xbe\xef

Rules

The input is of the form 0xXXXXXXXX and the output must be of the form \xXX\xXX\xXX\xXX. The input will always be 10 chars long and the output must be 16 chars long.

The score is the number of bytes used to write the encoding function. If the input string appears in the solution (i.e. not passed as an argument) it is not taken into account. The display of the result is implied (e.g. no need to print, puts, ...).

Answer 4

Implement Fizz Buzz in the C Preprocessor without the use if #if code-golf restricted-source

Note: I understand that there is already a question for Fizz Buzz and the preferred method is to place a bounty on an existing question instead of asking a new one. However, I believe that this warrants its own question.

The C Preprocessor Language is Turing Complete when used in a loop. Your task is to implement Fizz Buzz up to and including a given integer without the use if #if.

• You must be able to implement Fizz Buzz for inputs from 6 to 100. You can support more if you wish, but it is not required.
• #define INPUT <input> will be placed at the top of the file to provide input. This is not included in your bytecount.
• The output is defined as the output of cpp compilation with all lines beginning with # stripped away fed back into cpp for as many times as needed until the results of two steps are identical.
  • You must be able to prove this takes a finite amount of steps.
• Specify the version of the C Preprocessor Standard to use.
• No custom compiler flags.
• No using compiler extensions.
• You can delimit items with the delimiter of your choice.
• There can be extra delimiters at the start.
• Trailing newlines are allowed.
• #if is not allowed!
• It must be exactly Fizz, Buzz, and FizzBuzz. Case sensitive.

A submission might look like this:

#define MAIN(...) \ 
  // ... 
MAIN(INPUT)

It will be compiled as

#define INPUT <input>
#define MAIN(...) \ 
   // ... 
MAIN(INPUT)

...using the command cpp filename.

Steps for getting output:

1. cp file file2
2. cp file2 file
3. cpp file > file2
4. Remove all lines beginning with # in file 2.
5. If file2 is identical to file, exit. The current file2 is defined as the output.
6. Repeat steps 2-5 until exit.

Examples

Multiple outputs for a single input indicates all are valid

6 -> 1, 2, Fizz, 4, Buzz, Fizz
6 -> 1, 2, Fizz, 4, Buzz, Fizz, 
6 -> , 1, 2, Fizz, 4, Buzz, Fizz
6 -> , 1, 2, Fizz, 4, Buzz, Fizz, 
15 -> 1, 2, Fizz, 4, Buzz, Fizz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, Fizz Buzz,

Answer 5

Nibbles Nostalgia

People from my generation certainly know what is the Nibbles game! If you are not here included, what I am asking is a one-line version the level 1 of https://www.youtube.com/watch?v=UmeKHtei0qo (time: 14s—54s)

The challenge is to write a game that is a one line, one level Nibbles game using only the line buffer.

Rules:

• You must output to one or both of stderr/stdout
• Line Width is 80 chars
• Snake will always begin at the middle with 2 chars in width
• For a user to loose, the head of the Snake must hit one of the ends
• Each time a number {1...9} is catched the snake grows using the formula new_witdh= current_width + 2 * catched_number
• Of course numbers appear in an random position of the white space, never in Snake's body
• The char for each snake block body is ASCII \219 █
• It only accepts two keys, the Arrows for Left and Right. Does nothing when in the same sense; inverts head and tail when inverse
• First move is always to right
• It must be available somewhere online for me to play
• Timing between each turn of snake movement is 200 ms (This will be adjusted to make it more realistic)
• If user looses, you will output in the same line a full line of ASCII \127 char ⌂ and quit.
• If user wins, you will output in the same line a full line of ASCII \2 char ☻ and quit

It is a [code-golf] challenge, where there will be no accepted answer; I just made the challenge for my own fun!

UPDATE: I made a nice discovery: The original game is playable on http://stevehanov.ca/blog/index.php?id=92, by mouse clicking on Compile and Run

Answer 6

Caps Lock Morse Code

Inspired by Blink the CAPS LOCK

Input will be a string that contains only characters that can be represented in morse code.

Convert the input string to morse code and then output it using either the Caps Lock, Num Lock or Scroll Lock indicators on the keyboard

Thoughts on the challenge

• I think this would be good as a code golf
• How specific should I be on defining what the output looks like, is the above sufficient or should a specific time length be given for dots and dashes?

Answer 7

Free the Prisoners

code-golf

Your task is to free a few prisoners. Here they are, in their cells:

[sad] [shame] [cops]

---

Rules, explained

They have to be specifically freed using whitespace as replacement for each replaced letter, and then place the words to the right of the string, with an additional space separating the string area.

The first example would become:

[   ] [     ] [    ] sad shame cops

Here is a code snippet that lets you see the prison cell before and after, plus a JS function. The square brackets ([]) are assumed, and do not need to be typed in the box.

console.log(`Original Cell:     Waiting for input...`);
  console.log(`Emptied Cell:      Waiting for input...`);
  console.log(`Empty Cell Length: Waiting for input...`);

var string = '';
var emptyCell = function(string) {
  string = string.replace('[', '').replace(']', '');
  return ' '.repeat(string.length);
};

window.onkeyup = function() {
  string = document.getElementById('cagecontent').value;
  
  console.clear();
  
  console.log(`Original Cell:     '${string}'`);
  console.log(`Emptied Cell:      '${emptyCell(string)}'`);
  console.log(`Empty Cell Length: ${emptyCell(string).length}`);
};

<textarea id='cagecontent' placeholder='Place text, minus the brackets, here.'></textarea>

There is one known error for this script: the first bracket rule doesn't work. Sorry about that.

Any whitespace on the edge of an imprisoned string (ex. test with a space before) would stay while emptying the cells, but would be trimmed when placed outside. The aforementioned test with some extra whitespace on the edge would look like this:

[ test]
[     ] test

As you can see, instead of two spaces between the original string and the freeing area, there is only one.

[test]]
[    ]] test

Rules, simplified

• Trailing spaces are allowed.
• Replace each character in a prison cell string with a single blank space.
• Place each freed thing to the right of the original string.
  • Separate the original string and the freed things with a single space.
  • Extra whitespace on the sides of a string, when placed to the right of an original string, is removed.
• Your testing string will be: (Let us out!)>[mad] [angery] [11]]
  • Should result in: (Let us out!)>[ ] [ ] [ ]] mad angery 11
• No common loopholes, of course.

Scoring

If you look at the tags, you can see that this question is a code-golf puzzle. The tag wiki excerpt for this tag is:

Code-golf is a competition to solve a particular problem in the fewest bytes of source code. If you want to score by characters instead of bytes, please state this explicitly in the challenge. If source code length is not the primary scoring criterion, consider using another tag instead.

That means, the question (of any language) with the least amount of bytes is the top-scoring solution!

Answer 8

Is this bitstring divisible by 3?

code-golf binary string decision-problem

---

Your challenge is to write a program or function that, given a string of bits representing a positive integer, outputs or returns a truthy value if it's divisible by 3, and a falsy value otherwise.

Rules

• You may not convert the input to a number in any way. You may manipulate the string or loop through each digit, so long as you don't convert it to your language's native number type.
• Input may be given as a string or an array of digits.

Truthy examples

11
110
1001
1100
1111
10010
10101
11011
111111
10010011
1010010001
10101010101
100100101010001011110101010001
1000000000000000000000000000000000000000000000000001
1111111111111111111111111111111111111111111111111111
11000001001011110010001010001001010110000010100001001000100101
1111001111110010001110111011001010100100001000110100010011101011110010010111100111011100110101000011100110011111001010000111011110010111000100001010101001000001111011011111000101001111010010010010000110101100011001011111111000111001110110011011101010011000

Falsy examples

1
10
100
101
111
1000
1010
1011
1101
10000
11111
10101010101011
1101001000100001000001000000100000001
10000000000000000000000000000000000000000000000000001
11111111111111111111111111111111111111111111111111111
11000001001011110010001010001001010110000010100001001000100110
1101011111110011110010011101010011000001101011001111001001011010100000000110001111001101100000001010010111100111000101001001000011100000110111010010100000100001100101110000011010000010110010101011110010100110101100000011101101010000010011000001001001010101

---

Sandbox questions

Obviously as a Do X without Y question this is walking a very fine line. There are several string manipulation techniques (which I won't spoil here) that I'd like to see used, rather than solutions that just loop through the string and repeatedly add a digit and take modulo 3. I could be more strict and not allow any numbers in the process, but I don't know if that's a good idea... Suggestions? Is it even possible to make this a good challenge?

Answer 9

Leaderboard golf: posted

Answer 10

The Mass Murderers of Josephus

Everyone knows the Josephus challenge and its setup: you arrange n people in a circle, and the first person kills the second, and from then on the first alive person to the right of the previous "killer" kills the next alive person to their right. For example, with four people:

  1
4   2    (4 people in a loop)
  3

  1
4        (1 kills 2)
  3

  1
         (3 is closest to the right of the previous killer 1,
  3       and kills 4, who is to the right)

  1      (1 is closest to the right of the previous killer 3,
          and kills 3, who is to the right)

The last remaining person is 1, in this case.

Your task, however, is to find the most murderous of these people - or whoever killed the most people. In the above example, the "murderer" is 1, who killed 2 people: 2 and 3.

In a bigger example, of 10 people (this is a line of 10 people, right wraps around to the left):

PEOPLE ALIVE  | KILL TALLY
1 2 3 4 5 6 7 |
1   3 4 5 6 7 | 1: 1
1   3   5 6 7 | 1, 3: 1
1   3   5   7 | 1, 3, 5: 1
    3   5   7 | 1, 3, 5, 7: 1
    3       7 | 3: 2; 1, 5, 7: 1
            7 | 3, 7: 2; 1, 5: 1

There's a tie for the person with the most kills: when a scenario like this arises, the answer is average of all the people with the most kills - in this case, it is (3 + 7) / 2 = 5.

Task:

You must make a program or function that takes one input, the amount of people in the circle, and output the murderer (or the average of multiple murderers).

Rules and specs:

• The input will never be above 2^31 - 1.
• The input is guaranteed to be a positive integer.
• Your program must work out 100 within the timeframe of TIO (60 seconds). If you're not using TIO, provide an interpreter for me to test your program on (preferably an online one).

Answer 11

Chemistry 101

Question

Given the atomic number of an element in the range [1-118] print out the group and period, of that element as given by the following Periodic Table Of Elements.

For elements in the Lanthanide and Actinide series, (ranges [58-71] and [90-103]), you should instead print L for the Lanthanides and A for the Actinides

You may write a program or a function and use any of the our standard methods of receiving input and providing output.

You may use any programming language, but note that these loopholes are forbidden by default.

^{[Source] I couldn't have put it better!}

[Source]

Test Cases

The output here separates the group and period with a single space

| Input | Output |
|   1   |  1 1   |
|   33  |  15 4  |
|   45  |  8 5   |
|   71  |  L     |
|   93  |  A     |
|   117 |  17 7  |

Scoring

Simple code-golf. Shortest number of bytes wins

Answer 12

Android Lock Screen Art

graphical-outputpermutationscode-golfgrid

---

Background

In the land of Android, there exists a password type that looks like this:

It's essentially a connect-the-dots for a password. Today, we'll be making art with it.

The Task

Your program should export as many distinct combinations of pattern lock as image files with the following specifications:

1. Images should be 500x500 pixels large.
2. Dots should be located at positions (x, y):
   • (125, 125)
   • (125, 250)
   • (125, 375)
   • (250, 125)
   • (250, 250)
   • (250, 375)
   • (375, 125)
   • (375, 250)
   • (375, 375)
3. Lines should be drawn with a circular brush head of radius 8px.
4. Background color and line color may be any color of your choosing, but must not be the same color and it must be consistent.
5. The pattern should pass through all points ONCE, with the exception of the first point, which should be the first and last point drawn from/to.

Examples

The following output is valid (starts at top-left):

The following output is valid:

The following output is invalid:

This breaks condition 5 (repeat use of top-left, middle, and middle-left).

The following output is also invalid:

This passes through the top left twice and the start point is not the same as the end point (breaks rule 5 twice).

Scoring

The program with the largest number of distinct outputs wins, with the shortest program being the tiebreak.

Answer 13

All your base are belong to us 6 * 9 = 42

When Douglas Adams wrote THHGTTG, he just made up a formula for the answer to Life, the Universe and Everything. And then some spoilsport pointed out that it was a valid formula... when interpreted in base 13.

Given an input formula, please output as many bases as you can find where the formula is valid.

You must at a minimum support base 10 to base 16 inclusive, but you are strongly recommended to support base 2 to at least base 36.

You must at a minimum support the ()*+= operators, but you are strongly recommended to support - and /, and either ** or ^ for exponentiation. Note that the division will always be exact in valid bases, but may not be exact in invalid bases, so for 11/2=8 you should only output 15.

Examples

11/2=8
15

10+10=10*10
2

6*9=42
13

11**11=2101
3

This is code-golf, so the shortest answer that breaks no standard loopholes wins.

Answer 14

Unary-binary trees

Answer 15

Image Quine code-golf

The challenge is to quite simply, output an image of the source code of your program exactly as it is.

Scoring is by shortest source code wins.

The image must visibly contain the source code, and no other characters or decorations.

Standard quine rules apply, so:
- No 0-byte solutions
- No reading the source code

This is just a draft, so I'll make it more detailed should it be good enough to post.

Answer 16

Block Puzzle

A popular brain teaser commonly known as a the "IQ Block Puzzle" is comprised of 8 colored shapes which can be rotated, moved and flipped on a 8x8 grid. The puzzle is known as a geometric magic square.

Challenge

The challenge is to generate and then output all 40 possible pattern combinations that the pieces can be placed in.

The output can be in any form, but must somehow represent the position of all pieces, for example:

Combination 1 of 40:

  11113333
  12213333
  12214444
  22555448
  22555448
  66657788
  66657788
  66777788

...

There will be a winner for both:

• Shortest code in bytes
• Fastest calculation of all shapes in ms

Answer 17

Self-Generator code-challengequine

Challenge: Create a program that, given no input, outputs n programs (in the same language, but not necessarily the same language as the original program) separated by newlines, where each of those programs will print a section of the original program. When these sections are put together, it create the original program.

Your score is the number of bytes in the original program divided by (the number of sections that your code is split into) squared.

Answer 18

Average of a tune

code-golf math music

---

Often times when I'm bored, I'll find I have a catchy tune from a song stuck in my head. Then I notice the fingers on my right hand moving as if playing that tune on a piano. If I have nothing better to do, I'll spend some time calculating where on the scale I need to play so that all five fingers get optimal usage. For example, given the tune

C4 C4 G4 G4 A4 A4 G4 F4 F4 E4 E4 D4 D4 C4

I try to center the notes such that if they were weights arranged on a board, the board would balance on my middle finger. (That's probably not a tune I'd have stuck in my head, but you get the idea.) In this case, the notes can be arranged like so:

C4          G4
C4 D4 E4 F4 G4 A4
C4 D4 E4 F4 G4 A4
=================

Now we have to balance the board. If the fulcrum is placed under E4, it will be equivalent to summing the following weights:

-2          +2
-2 -1  0 +1 +2 +3
-2 -1  0 +1 +2 +3

The result is +6, indicating that the board is leaning to the right. So we try moving right so that the fulcrum is under F4, which gives us the following:

-3          +1
-3 -2 -1  0 +1 +2
-3 -2 -1  0 +1 +2

The sum is -8, indicating that the board is leaning to the left, and also leaning further than it had before; therefore, the optimal middle note is E4.

By this point I've usually wasted all the time I had at my disposal, plus a good bit more. So your task is to write a program or function that does this calculation for me. Since I have more important things to waste my memory on, your code should be as short as possible.

Task

Write a program or function which takes in a list of notes and outputs the average of these notes.

• Only notes on the scale of C major (C, D, E, F, G, A, B) should be taken into account; you never need to deal with sharps or flats.
• The notes can range from C0 to B9, inclusive; you'll never get A-1 or C12.
• The input can be given as an array, or as a string separated by spaces, newlines, commas, etc.
• The input will always contain at least one note.
• Input/output can be given in whichever case is desired. If your code only accepts one case or the other, make a note of this in your answer.
• If there are two valid outputs for a given input, you may output either or both.

Test cases

Input -> Output(s)
C3 -> C3
C0 -> C0
B9 -> B9
C3 C3 -> C3
C3 D3 -> C3 or D3
C3 E3 -> D3
C0 B9 -> B4 or C5
C3 C3 C3 -> C3
C3 C3 D3 -> C3
C3 C3 E3 -> D3
C4 D4 E4 F4 -> D4 or E4
E4 E4 E4 C4 E4 G4 G3 -> D4
C3 D3 E3 F3 G3 A3 B3 C4 -> F3 or G3
C3 C3 E3 F3 G3 A3 B3 C4 -> F3
A3 A3 A3 C4 A3 A3 A3 A3 G3 F3 E3 -> A3
C5 D4 C4 C5 D4 C4 A4 C5 D4 C4 C5 D4 C4 -> F4
C4 C4 G4 G4 A4 A4 G4 F4 F4 E4 E4 D4 D4 C4 -> E4
E3 E3 F3 G3 G3 F3 E3 D3 C3 C3 D3 E3 E3 D3 D3 -> E3
C4 C4 E4 E4 A3 A3 C4 C4 F3 F3 A3 A3 G3 G3 B3 B3 -> B3
C3 C3 E4 E4 A2 A2 C4 C4 F2 F2 A3 A3 G2 G2 B3 B3 -> E3
A3 A3 A3 G3 A3 A3 A3 B3 B3 C4 C4 C4 B3 C4 G4 G4 B3 B3 -> B3
G3 G3 A3 G3 C4 B3 G3 G3 A3 G3 D4 C4 G3 G3 G4 E4 C4 B3 A3 F4 F4 E4 C4 D4 E4 -> B3
B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 B9 A6 -> A9

^{(Imaginary bonus point for each song you recognize)}

Scoring

Since this is code-golf, the shortest code in bytes in each language wins.

---

Sandbox questions

• Is there a plain "average of an array of integers" challenge, and would this be a duplicate?
• Is anything unclear, or does any information need to be added?
• Suggestions for a title? I feel like there's a "tuna fish" pun waiting to be made...
• Suggestions for test cases?

Answer 19

Multiplivision

Hopefully a nice simple challenge that's not trivial.

Given an input list of positive integers, alternately multiply and divide them to yield a single numerical answer, according to the following rules:

• start with the first number;
• with the remaining numbers, alternate between dividing and multiplying, one at a time (that is, in a left-associative way), with the last operation being multiplication

For example, the input {3, 4, 2, 7} would start with 3, then successively compute 3 * 4 = 12, then 12 / 2 = 6, then 6 * 7 = 42 and output 42. (In other words, the input {3, 4, 2, 7} yields the output (((3 * 4) / 2) * 7) = 42.) The first operation had to be a multiplication, because if we'd started with a division, then the last operation would have been division as well, which isn't right.

If the answer is not an integer, then it can be output either as an exact fraction, or as a decimal equivalent, accurate to at least 6 significant figures (either truncating or rounding the end of the decimal is fine). For decimals that terminate before 6 significant figures, either the terminating decimal alone (1.5) or a version with trailing zeros (1.50000) is fine.

Other test cases (only the numerical answer needs to be output, not the intermediate parsed expression):

{3} -> 3
{3, 4} -> 3 * 4 = 12
{3, 4, 2} -> 3 / 4 * 2 = 3/2 or 1.5
{5, 4, 3, 2} -> 5 * 4 / 3 * 2 = 40/3 or 13.3333
{1, 2, 3, 4, 5, 6, 7, 8} -> 1 * 2 / 3 * 4 / 5 * 6 / 7 * 8 = 128/35 or 3.65714
{42, 42, 42, 42, 42, 42} -> 42 * 42 / 42 * 42 / 42 * 42 = 1764
{42, 42, 42, 42, 42, 42, 42} -> 42 / 42 * 42 / 42 * 42 / 42 * 42 = 42

This is code-golf, so the shortest code in bytes wins! Golfed answers in all languages are welcome.

Answer 20

King of the Hill: Risk(k)

king-of-the-hill game c# c++ .net windows

We all know these well spend evenings where family members and friends got to temporary enemies while playing Risk the board game. The rules are not so complicated, the world is divided in territories on 6 different continents. The different players take control over those territories and afterwards play to conquer the neighbors, form alliances and betray each other until one player reaches world domination.

But wouldn't it be cool, if you just write a bot for you to play this game? here comes your chance.

This is a King of the Hill challenge to write the best bot to play Risk(k). Like in the original game (but not entirely) the world is divided into 6 continents with a total of 41 territories. Afterwards the bots will play this game with reduced rules in a round-based setting. Your bot can be written in c# or c++. Although any other language is possible which is capable of producing a dll with cdecl-functions or to implement .net interfaces. The controller can be found on Github.

A short classis-game explanation

For all of you, who aren't familiar with this game. Every player plays on his own against all other players. The game begins with the claiming of territories (by positioning a single unit there) which is done consecutively for every player until all territories are owned by a faction. Now the players get the chance of using all units they have left to enforce their territories. Now the game begins round-wise. Every player makes a Attack-Stage and Move-Stage. In the attack-stage the players can attack other territories. This is done with dices. When thrown (the attacker and defender), the dices on each side are ordered and the highest ones are compared to each other. Whoever has the higher dice destroys a unit of the opposite side. Equal dices are considered a tie and no unit dies. You can only attack with max. 3 units at the same time, even when you have more than 3 units on your attacking territory. Also a territory with one unit cannot attack to prevent territory loss. Likewise a territory with two units can only attack with one etc. . When a territory falls to zero units, the attacking territory has to send units over (at least on and max. all except one - in the controller, all units except one are send automatically). After the attack stage, one player gets the chance to move units in the Move-Stage. One can only do so, if the territories you want to move units between are connected by territories owned by you. If your are done with this, the next players turn begins. The game ends, when one player has conquered the whole world.

The game&rules:

• All bots have to obey the rules. Cheating bots will be punished by the program or by me. Standard loopholes are forbidden.
• Each bot must be in a dll file (name.dll) in the same directory, as the controller.
• Each program with the c++ interface must end with name.cpp.dll
• When the program is started each bot gets loaded into the program and is checked if everything works. The bots get instantiated only one time when the game starts.
• All bots loaded are participating in the game.
• The initialization stage begins:
  • Each bot gets asked through the interface about its name and color.
  • All bots get introduced to another with their names.
  • All bots get consecutively called to select one of the remaining free territories. This goes till no territory is free anymore.
  • All bots get to distribute the units left to all territories. [UnitCount = Ceil(82 / BotCount) ]
• The game will stop for now till the user pushes the start-button.
  • The game will be round based where each bot will get consecutively called in four stages: Strategy-Stage, Enforcement-Stage, Attack-Stage, Move-Stage
  • The Strategy-Stage gives your bot the opportunity to plan a strategy for this round.
  • The Enforcement-Stage will give your bot the opportunity to distribute all new units to your territories. Units are gained to: Count of owned territories divided by 5 and floored, continent-bonus (owning a whole continent: North America: +5, South America: +2, Europe: +5, Africa: +3, Australia: +2, Asia: +7), capital-bonus (+1 for each owning of: East US, Brazil, North Europe, South Africa, East Australia, China) and +1 if you conquered a territory last round. You're guaranteed to get at least one new unit per round if your bot is still alive.
  • In the Attack-Stage you can order the program do make attacks on enemy territories which can lead to loss on your or the enemy side or you conquering a new territory. The attack will be called multiple times (max.: 100 times) as long as you make an attack every call.
  • In the Move-Stage you can move units around owned, connected territories. You can also again plan your strategy there for the next round.
  • Each round is time constricted for every bot with 200ms. Taking longer than this will lead to a punishment (suspension) for the next round.
• The game ends when only one bot still lives or when two bots get into an infinite loop (which is surprisingly possible and not rare for the random-bots)

The controller&interface

How the interfaces work is explained in the template files and the example-bots.

For c#, .NET Programmer

Your bot has to be in a class which inherits and fully implements the IBotInterface. The class must be compiled into a class-library (dll). Afterwards you can just copy your dll into the game-directory and start the game.

EmptyBot is an empty template which implements the minimum required and adds a lot of useful helper-methods. It can be used as a template.

RandomBot is a bot which implements random behavior in all functions and stages. It acts as a full working example.

For C++, C, cdecl-function-able-languages

Your dll must implement eight functions with an external definition and cdecl-calling convention. A minimal implementation can be looked at at EmptyCPPBot.

Your dll can afterwards be copied into the game-directory which can be started normally afterwards. Your dll must have the following name structure: nameOfYourDll.cpp.dll to distinguish it from the managed dll's.

RandomCPPBot is a bot which implements random behavior in all functions and stages. It acts as a fully working example.

Contest Rules

• Players may submit multiple bots and are free to edit them to the deadline.
• A submission must be made as an answer on this thread. The source code can come in pieces, as full project, single file or whatever. And may be provided via download, push request or simple pasted code in the answer with code-tags. If not compile-able with Visual-Studio, i request fairly simple instructions how to compile it myself.
• A submission must specify the name and color of the bot. Although not necessary, an explanation of the bot's strategy would be nice.
• Bots are not allowed to use sources outside the dll/program (no files, no webrequest or similar things).
• Bots must be compatible with the provided interface and work under windows. Custom interfaces are not explicitly forbidden as long as they don't generate a advantage or are not compatible with the main-interface/program.
• The competition will be held in the provided controller (possible altered to automate the process) with all pairings possible to find the best 4 bots.
• The last 4 bots are fighting each other in 10 games. The bot which has won the most, wins the tournament. In a tie situation, the bots will take a single match against each other (golden goal), until one wins.
• Rules are can be changed when necessary which would be introduced on top of this thread.
• The contest ends when a week long no new submissions got made or when I say, its time to end this.
• And again, just to be sure: standard loopholes are forbidden.

Answer 21

Check for repeated repeated words

Task

Your code should either read in a stream/file containing printable ASCII text or define a function that takes a string containing printable ASCII and output any repeated words (including their repetitions). If you read from a file then it can have a name of your choice. Output can be a single linefeed-separated string, or a list of strings (one per repeated word).

A word is defined by the regex [0-9A-Za-z'-]+, i.e. it's a run of letters, digits, apostrophes and/or hyphens.

A word is considered to be repeated if it occurs twice or more in succession, separated only by one or more spaces. Repetition is case sensitive: WORD, Word and word are all different.

Test Cases

Individual test cases are separated by an empty line. For each test case, the first line is the input, subsequent lines are the output. Note that the last test case does not contain any repeated words.

Hello how how are you?
how how

Hello my my friend. Is that that your pen pen pen?
my my
that that
pen pen pen

This is not. not a case of repeated? repeated words! Neither neither is this. 

code-golfstring

Answer 22

Island Golf #3: Random Generation

code-golf ascii-art random generation grid

Given the dimensions of a rectangular patch of ocean and the desired number of land tiles, randomly generate a valid island of that many tiles within that rectangle.

Input

Your input will be three positive integers:

• w, the width of the grid
• h, the height of the grid
• n, the number of tiles to make the island

w and h will always be 3 or greater. n will always be 1 or greater. Also, n will be small enough to fit inside the grid allowing for a border of water tiles: specifically, n <= (w-2)*(h-2).

Output

Your code must output a w by h rectangular grid consisting of two characters, representing land and water. (In the examples below, land is # and water is ., but you may substitute any two distinct characters you wish.) There must be exactly n land characters, in one contiguous block, representing an island. For example, an input of w=11, h=9, n=40 might result in the following output:

...........
...##......
..#####....
..#######..
.#########.
...#######.
...#####.#.
....####...
...........

Requirements:

• The land tiles must all be contiguous (i.e. there's only one island).
• Land tiles can be connected horizontally or vertically, but not diagonally.
• The water tiles must also be contiguous (i.e. there must not be any lakes).
• The outer border of the grid must remain as water tiles.

Some illegal outputs:

.....
.#.#.   Multiple islands
.....

....
.#..    Diagonal connection
..#.
....

......
.####.  Contains a lake
.#.##.
.##...
......

....
.###    Border contains a land tile
.##.
....

Details

Your solution may be a full program or a function. Any of the default input and output methods are acceptable. Any of these definitions of randomness are acceptable. Every valid island for a given input should occur with nonzero probability.

You may take the input numbers in whatever format and base is convenient for your language. You may take the three numbers in any order.

Your output may be a multiline string, a list of strings, or a 2D array/nested list of characters/single-character strings. Your output may (optionally) have a single trailing newline. As mentioned above, you may use any two distinct characters in place of #..

Please mention any unusual I/O methods/formats in your submission, so others will be able to test your code more easily.

Test cases

Given as width, height, size. Note that the first three test cases specify islands of maximal size for the given width and height.

3, 3, 1
9, 3, 7
5, 5, 9
5, 5, 1
10, 10, 60
80, 22, 1100

Validation program

Here is a validation program in Pip to test whether your output for a given input meets the spec. It expects the three parameters and an island in the format given in this question; for example:

5, 5, 9
.....
.###.
.###.
.###.
.....

If your code has a different output format, you'll need to convert it to this format before plugging it into the validation program.

---

Sandbox questions:

• This seems like a pretty obvious random-generation challenge, but I didn't find a duplicate in a quick readthrough of previous random challenges. Did I miss anything?
• Should I add more stringent rules on what counts as random? Related reading
• Should I allow output to be a 2D array (or nested list) of any two distinct values, not just chars and single-char strings? (E.g. integers 0 and 1, booleans false and true, etc.)

Answer 23

Calculate Wind Chill

math arithmetic code-golf number

---

The Australian Apparent Temperature (aka, wind chill) in °C AT is given by this algorithm from the Australian Bureau of Meterology (wp, source):

AT = Ta + (0.33 * e) - (.7 * ws) - 4.0

Where:

Ta = Dry bulb temperature (°C)

e = Water vapour pressure (hPa)

ws = Wind speed (m/s) (at an elevation of 10 meters)

The water vapour pressure in hectoPascals e is given by this algorithm:

e = (rh / 100) * 6.105 * exp( ( 17.27 * Ta ) / ( 237.7 + Ta ) )

Where:

Ta = Dry bulb temperature (°C)

rh = Relative humidity [%]

exp represents the exponential function

The domain of:

• Ta is -273.15°C to 2e7°C.

• e is the real numbers

• ws is 0 m/s to 2e7 m/s

• rh is 0% to 100%

For inputs outside these domains, your code can do anything, including give the right answer.

---

Output

Given a dry bulb temperature in °C, a wind speed in metres / second, and a relative humidity in %, your code should give the Apparent Temperature in °C, accurate to 0.1°C.

Assuming your platform or language can represent reals, for correct functions correct_func,

or in C, fabsl( correct_func(Ta, rH, ws) - expected ) < 0.1.

Test cases

value for Ta, rh, ws -> output

0   ->  -4.0
2   ->  -3.3529916671770903
4   ->  -2.6916697830145546
6   ->  -2.0132006039049877
8   ->  -1.3143308806029346
10  ->  -0.5913412821173161
12  ->  0.16000376605969002
14  ->  0.9445099696431676
16  ->  1.767610915646344
18  ->  2.6354298170017625
20  ->  3.5548453789325833
22  ->  4.5335619088440815
24  ->  5.580183785538598
26  ->  6.704294397098089
28  ->  7.916539649854112
30  ->  9.2287161435045

You can use a builtin function for the exponential function, ex, if you like.

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

Answer 24

Factor Sort

This challenge involves sorting positive integers based on a lexicographical ordering of their prime factorizations.

Overview

lexicographical sorting, used in dictionaries, applies lexicographical order which extends alphabetical order to words:

a
aa
aaa
aaron
ab
abandoned
abc
aberdeen

When programming this sort, however, we typically don't extend alphabetical ordering per se, but rather we extend the order of integers used for an encoding. For example, the same sorting above through ASCII encoding is really:

97
97 97
97 97 97
97 97 114 111 110
97 98
97 98 97 119 100 111 110 101 100
97 98 99
97 98 101 114 100 101 101 110

It is this type of ordering that we're after here... lexicographical ordering by extension of numeric comparison as opposed to alphabetical order.

The Challenge

In this challenge, you will be sorting positive integers by their ordered prime factorizations (ordered in the sense that the primes are listed smallest to largest). To handle the special case number 1, we can simply say its prime factorization is an empty list, which lexicographically sorts prior to any other number's prime factorization. We'll call this type of sorting factor sorting.

For example, the numbers from 1 to 10, factor sorted, are: 1 2 4 8 6 10 3 9 5 7. To see why, here they are again with the ordered prime factorizations:

 1 []
 2 [2]
 4 [2 2]
 8 [2 2 2]
 6 [2 3]
10 [2 5]
 3 [3]
 9 [3 3]
 5 [5]
 7 [7]

Rules

Write a function or program that factor sorts a list of positive integers. Input and output can be anything reasonable, so long as the input is in the specified arbitrary order and the correct output order is apparent from the output.

Keep in mind that the output should be factor sorted numbers, not their prime factorization.

If it matters, numbers in the input will always be ≤ 7928, so:

• The only primes in the prime factorization list are the first 1000 primes
• Composites have factors no larger than 89 inclusive

This is code golf; shortest code in bytes wins.

Test cases

1 2 3 4 5 6 7 8 9 10
->
1 2 4 8 6 10 3 9 5 7

100 200 300 400 500 600 700 800 900
->
800 400 600 200 900 300 100 500 700

1472 4417 1425 1452 4480 200 339 2868 3835 4760
->
4480 1472 200 4760 1452 2868 1425 339 3835 4417

2 4 6 46 62 466 622 4666 6238
->
2 4 6 46 62 466 622 4666 6238

code-golf sorting number-theory

Answer 25

Dice Roller

Since I have played a lot of tabletop role playing games, I am looking for an easy to use dice roller. But also being lazy, I would like to have the shortest possible solution, making this code-golf.

Input

You will receive as input a string, composed of 2 or 4 variables.

In the case of 2 parameters, both non-negative numbers, they represent the number of dice and the value of the dice rolled.

Examples:

"2 6" means rolling 2 6-sided die (colloquially written 2d6).
"3 8" means rolling 3 8-sided die (3d8).

In the case where 4 parameters are given, the first 2 are still numbers, as in the case of 2 parameters. The third and forth parameters represent a dice modifier, and whether the modified applies to the dice individually or the sum of all rolled values, respectively. The third parameter is a (possibly) signed number (e.g.: 2, +1, -2, ...), and the forth is a character string, either 'ind' (if the modifier applies to the individual dice) or 'all' (applies to the total sum of the dice rolled).

Examples:

"2 6 +1 ind" means rolling 2 6-sided die, and a modifier of +1 is applied to each individual die (can be written 2d(6+1)).
"3 8 -4 all" means rolling 3 8-sided die, and a modifier of -4 is applied to the sum of the roll (can be written (3d8)-4).

Dice Properties

• Only the following dice are acceptable (second parameter): 2 3 4 6 8 10 12 20 100.

• Regardless of modifier, a dice gives at least a value of 1 when an individual modifier is applied (so for example, "1 6 -10 ind" will return a value of 1, the minimum value allowed by this stipulation). There is no max value to an individual modifier.

• When a modifier is applied to the sum of the dice rolled (4th parameter is "all"), the sum can be less that the number of dice rolled. For example, "2 6 -20 all" will give a sum range of -18 to -8, as the lowest value of 2d6 is 2 and highest value is 12, pre-modifier. There is no min or max value to a this modifier.

Output

The output will be the values of the individual dice rolled, and the sum of all the dice.

Valid examples:

"2 6" => "3 6 : 9"
"3 8" => "1 8 5 : 14"
"2 6 -1 ind" => "1 2 : 3"
"2 6 -10 ind" => "1 1 : 2"
"3 8 +1 ind" => "2 9 6 : 17"
"2 6 10 all" => "3 6 : 19"
"2 6 -10 all" => "3 6 : -1"

Invalid examples (incorrect results):

"2 6" => "3 7 : 10" (7 is not a valid result on a 6-sided die)
"3 8" => "1 8 : 9" (not enough dice rolled)
"3 8" => "1 8 5 4 : 18" (too many dice rolled)
"2 6 -1 ind" => "1 6 : 7" (6 is not a valid result on a 6-sided die with a -1 modifier applied)
"2 6 -1 ind" => "0 5 : 5" (the die has to have a minimum value of 1 with individually applied modifier)

Answer 26

Find the Translation Table code-golf translation

Given two strings, find the translation table between the two, if the translation is not possible, output false. Probably most easily defined through examples:

Valid Cases

bat,sap = ["bt","sp"]

sense,12312 = ["se","12"]

rabid,snail = ["rabd","snal"]

Falsy Cases

banana,angular = false (not the same length, impossible).

animal,snails = false (different character patterns, not a translation).

Rules

• Input may be as a 2 element array or as 2 separate inputs.
• Output can be as an array, on separate lines or space delimited, but must be similar to how I have it shown.
• False output may be 0, -1 or false. If your language uses something different, ask.

Sandbox Questions

Should I allow inputs of different length to be part of the translation? This will increase the complexity of the question by 100%. I'd suggest using - as the marker for a removal of a character in the translation to make it work. While it makes it more complicated, if this already exists I planned to use that to avoid a duplicate. Let me know what you think. I really like the extension idea though.

Answer 27

QR Code Editing: Minimum Change

code-challenge? This is pretty non-trivial, and finding optimal solutions is probably computationally difficult.

QR codes are a way to represent URLs and other strings of text using a 2D image. What you might not know, however, is that a significant portion of a QR code is error-correction or unused space.

In this challenge, your program will be given a square of 1s and 0s representing a QR code. This QR code may not be functional, or it may be valid or point to some destination. Your program will also receive a string, representing the data that the new QR code should be encoded with. The goal of the program is edit the original QR code to contain the new content, but also to do it with as few pixel-flips as possible.

Here's an image describing some parts of the QR format:

QR code art generator, demonstrating how much of a QR code's space can be modified without changing the content: https://www.qrpixel.com/

Spec is only partially completed, I'll probably have to find some decent resources on QR code formats and error correction.

Answer 28

Pratt certificates

(bumping this proposal to see if there's any interest or comments. If so, speak now; if not, I'll delete)

Your task: write code that generates a Pratt certificate for a prime number, and write code that verifies an existing Pratt certificate.

What's a Pratt certificate?

A Pratt certificate for a prime number p is a proof, of a particular type, that p is indeed prime. Historically, it was used in situations where proving the primality of p required a computation that was slow due to factoring p-1, but verifying the certificate (once the initial computation generated it) was quite fast.

A Pratt certificate for p is a recursive structure consisting of three parts: the prime p itself; a "witness" integer g (which is actually a primitive root modulo p; see the next section for its properties); and Pratt certificates for all primes dividing p-1. The prime p=2 is special: a Pratt certificate for 2 is just 2 itself.

For example, here is a Pratt certificate for p=3911:

{3911, 13, {2, {5, 2, {2}}, {17, 3, {2}}, {23, 5, {2, {11, 2, {2, {5, 2, {2}}}}}}}}

The witness is 13, and the prime factors of 3911-1 are 2, 5, 17, and 23; each of those new primes itself has a Pratt certificate, which are respectively 2, {5, 2, {2}}, {17, 3, {2}} and {23, 5, {2, {11, 2, {2, {5, 2, {2}}}}}. In this last Pratt certificate, the prime factors of 23 are 2 and 11, so a Pratt certificate for 11 must be included, and so on.

How do we generate a Pratt certificate?

Given a prime p, a Pratt certificate can be generated by finding a primitive root g modulo p; factoring p-1 into primes (keeping only one copy of each prime factor); and recursively generating Pratt certificates for every prime factor of p-1.

How do we verify a Pratt certificate?

Given a prime p, a witness g, and the prime factors q1, q2, ... of p-1, a Pratt certificate is verified by checking:

• that p-1 has no prime factors other than q1, q2, ...;
• that the power g^(p-1) is congruent to 1 modulo p;
• that none of the smaller powers g^((p-1)/q1), g^((p-1)/q2), ... are congruent to 1 modulo p; and
• that each of the Pratt certificates of q1, q2, ... are themselves valid.

Scoring and technicalities

You must write two programs or functions (or one of each): one that takes a prime number as input and returns its Pratt certificate; and one that takes an input formatted like a Pratt certificate and returns a truthy or falsy value depending on whether it is an actual Pratt certificate.

• You may choose any reasonable format for the Pratt certificate: nested lists (like the examples in this question), indented multiline strings (like the example on the Wikipedia page), or something similar that a human being could be trivially trained into parsing by eye. You may use any reasonable convention for the trivial Pratt certificate for 2.
• However: whatever format you choose for the Pratt certificate, your certificate-generating code must output the same format that you take as input to your certificate-verifying code. Note that your certificate-verifying code must be capable of verifying any possible Pratt certificate (in your format) for p, not just the one your other program generates for p.
• If you want, you may write a single program or function that accomplishes both tasks; in that case, your code can either determine which task is being asked of it implicitly from the input, or it can allow the user to instruct it which task to perform in some reasonable way.
• Regardless of whether you use one or two programs, no calculation can be shared or saved between different runs of the code. The programs must work correctly, on any individual prime input and on any individual certificate-shaped input, if it is the first time that code is ever being run on that system.
• You don't have to handle bogus input. You may always assume that the input to your first program is an actual prime number, and that your input to the second program syntactically matches your Pratt certificate format.
• Built-ins that generate or verify Pratt certificates are not allowed. Other types of built-ins (for example, those that factor integers, raise integers to powers in modular arithmetic, find primitive roots) are acceptable.
• This is code-golf, so shorter code (in bytes) is better. If two programs are used, the total number of bytes in both programs is the score; if one program is used, its number of bytes is the score.

Example Pratt certificates given prime inputs

(Note that there are many possible witnesses for any given prime, but the rest of the certificate is unique up to reordering.)

31 -> {31, 3, {2, {3, 2, {2}}, {5, 2, {2}}}}
127 -> {127, 3, {2, {3, 2, {2}}, {7, 3, {2, {3, 2, {2}}}}}}
229 -> {229, 6, {2, {3, 2, {2}}, {19, 2, {2, {3, 2, {2}}}}}}
1093 -> {1093, 5, {2, {3, 2, {2}}, {7, 3, {2, {3, 2, {2}}}}, {13, 2, {2, {3, 2, {2}}}}}}
65537 -> {65537, 3, {2}}

(All the above outputs are examples of truthy inputs for the Pratt-certificate checking code.)

Example falsy inputs for Pratt-certificate checking

{31, 2, {2, {3, 2, {2}}, {5, 2, {2}}}}
{31, 3, {2, {3, 2, {2}}}
{31, 3, {2, {3, 2, {2}}, {5, 2, {2, {3, 2, {2}}}}}}
{127, 2, {2, {3, 2, {2}}, {5, 2, {2}}}}
{85, 4, {6, 5, {5, 2, {2}}}, {14, 3, {13, 2, {2, {3, 2, {2}}}}}}

Answer 29

Median fractals

code-golfgraphical-outputfractal

I define 'Median fractal' as this.

Median fractal L₁ is a equilateral triangle.

for median fractal L_n, Draw L_n-1, then for each triangle, draw all 3 medians in the triangle.

You will be given an integer n, draw L_n.

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Sandbox

Any suggestions, guys?

Answer 30

cops-and-robbers These would be separate questions, and each would link to the other.

Cops: Make a bad password policy

Over the years, people have come up with some pretty bad password policies. Your challenge is to make such a policy, and to make a program that takes advantage of the weakness of this policy to brute force passwords written in it (a "crack"). For details on what constitutes a "crack", see the robber thread [link]. It should restrict the user to as small a selection of passwords as possible. Robbers will attempt to find cracks for your policy. If your answer is uncracked after 7 days, you make mark it safe by posting your crack. The "worst" uncracked policy (that is, the one that allows the fewest passwords) wins.

A "policy" is defined as a list of well-defined restrictions ("rules") on valid passwords. Here is an example:

• Passwords must contain only digits, letters, and the characters '*&^'.
• Passwords must be at most 8 characters long.
• Passwords must not contain dictionary words (if you use this one, you must use a freely and programmatically accessible dictionary and tell us where to find it).

Policies:

• must contain no more than 10 rules,
• may not involve encryption of any kind, and
• must be clear and unambiguous

For example, these would be a bad rules:

• The MD5 hash or zipfile of the password must not contain the letter "a". (Uses encryption of a sort)
• Passwords may not contain special characters. (It's unclear what counts as a special character)

Your answer must contain both the policy and the number of passwords it allows.

Robbers: Crack the bad password policy

Over the years, people have come up with some pretty bad password policies. Your challenge is to crack such a policy. These can be found in the cops thread [link]. To crack a policy, write a program to brute force passwords that adhere to that policy. Your program must run in linear time on the number of possible passwords allowed by the policy. You may do this by enumerating or iterating over all possible passwords in some way, such as by calling a function (called, for example, guessPassword) for each possible password. One option is to simply hardcode the possible passwords, if there are only a few. Here is an example (JavaScript):

function* getPasswords() {
    yield* ['a', 'b', 'c'];
}

Or, using the second approach:

function bruteForce() {
    for (let pw of ['a', 'b', 'c']) {
        if (guessPassword(pw)) {
            return pw;
        }
    }
}

Whoever cracks the most policies wins.

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Sandbox

• Is the linear time approach good? My original thought was just "your program must halt in a reasonable time", but that seems too vague, and this allows a person to crack even policies with a lot of possible passwords (though those hopefully wouldn't win anyway).
• I could also just say, "pick a password in your policy and robbers will try to crack it", maybe having the cops supply a hash of the password.