Sandbox for Proposed Challenges

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Answer 1

Print the SARS-Cov-2 (COVID-19) genome code-golf kolmogorov-complexity

Background

As you probably learned in biology class, DNA and RNA are composed of strands of nucleotides; each nucleotide consists of a chemical called a base together with a sugar and a phosphate group. The information stored in the DNA or RNA is coded as a sequence of bases. DNA uses the bases A, C, G, and T (standing for adenine, cytosine, guanine, and thymine), while RNA uses A, C, G, and U (with uracil replacing thymine).

Challenge

The genome of SARS-Cov-2, the virus that causes COVID-19, has been fully sequenced. This genome is a sequence of 29,903 bases, each base being one of A, C, G, or U, since it's an RNA virus.

The challenge is to output that sequence using as few bytes in your program as possible (code golf). You can write either a full program or a function.

Because the names A, C, G, and U are arbitrary, you can use any 4 characters you want instead:

• You must use exactly 4 characters (they must be pairwise distinct--two or more can't be equal).
• Each one of the 4 characters must be a printable ASCII character in the range from '!' to '~', inclusive (ASCII 33 to 126). In particular, this does not include the space character or the newline character.
• Each of the 4 characters you use must always represent the same one of A, C, G, and U -- no changing in the middle!

Your output should be the precise text at the following link, with A, C, G, and U replaced by whichever 4 characters you selected, and you may optionally follow the entire sequence with one or more newline characters (but no newlines or other extraneous characters at the beginning or in the middle are allowed):

Click to see the required output. (Including all 29,903 characters here would cause this to exceed a StackExchange maximum size.)

Because you can use any 4 distinct characters you want, it's acceptable to use, for example, lower-case instead of upper-case, or to use T instead of U, or to use 0123 instead of ACGU, or even to output the complementary strand (with A and U switched, and C and G switched).

Restrictions

Standard loopholes are prohibited as usual. In particular, it's not allowed to retrieve information online or from any source other than your program. You also can't use any built-in which yields genomic data or protein data (these would generally retrieve data from the Internet so they wouldn't be allowed anyway, but some languages may have this facility built in internally; use of such functionality is prohibited whether implemented internally or externally).

Verifying Your Program

I've set up a way to check that your program's output is correct. Just copy and paste your program's output into the argument in this verification program on TIO and run it.

Other Info

Some facts that may or may not be of help:

1. There are 29,903 bases in the sequence. The counts for the individual bases are:

   • A 8954
   • C 5492
   • G 5863
   • U 9594

2. If you simply code each of the 4 bases in 2 bits, that would get you down to 7476 bytes (plus program overhead), so any competitive answer is likely to be shorter than that.

3. The source for the data can be found at this web page at NIH; scroll down to ORIGIN. The data is written there in lower-case letters, and 't' is used instead of 'u', apparently because DNA sequencing techniques were used.

4. There are variant strains of SARS-Cov-2 known (the base sequences are slightly different, and the length varies a bit); I believe the one here is the first one sequenced, from Wuhan.

5. Groups of 3 consecutive bases code for particular amino acids, so it might be useful to analyze the data in groups of 3. But there are non-coding areas where the number of bytes isn't necessarily a multiple of 3, so you may not want to just divide the data into groups of 3 starting at the beginning. If it might be useful, you can find more info on the structure of the virus RNA here (but this probably isn't needed).

Disclaimer: I'm not a biologist. If anyone has any corrections or improvements on the underlying biology (or anything else, of course), please let me know!

Happy golfing!

Answer 2

Pwning Passwords code-golf

Alice decided to improve the security of her website by sending first five characters of an SHA-1 hash to Bob's Leaked Password Detection Service. However, she made two mistakes that let Eve decode the passwords: sending passwords over HTTP and checking the password after each character of a password is typed. Eve asked you for help in decoding the passwords, however she cannot really program, so needs your help in implementing password cracking algorithm as a computer program or function.

Eve eavesdropped the requests for following hashes from Alice.

516B9
379FC
19C2A
9D4E1
08506
F808E
A7F93
5BAA6

How could you decode this password? Well, you can brute-force all lowercase letters. In this case the only letter whose hash starts with 516B9 is p. The hash of letter p is 516B9783FCA517EECBD1D064DA2D165310B19759.

Knowing that the password starts with p, you can brute-force the second character. In this case, the only possible character is a. The hash of pa is 379FC0D5299A71AC0F171FBB5AFB262829B4E765

You can continue to brute-force letters one by one to figure out the password was password (5BAA61E4C9B93F3F0682250B6CF8331B7EE68FD8). Well, that was simple.

Not all passwords are that simple however. Consider the following requests:

4DC7C
A84FD
467D7
BD79D
12D83

First three characters of this password are simple: rxr (467D7856C648A79A096D339A2CE5FC929658967D).

With the fourth character it gets more complicated. BD79D matches for rxrf (BD79DEC8435B8BA509A25F419F31CC2ACDE2FF0A) and rxrp (BD79DC20901B11468F8369B5B0D15894F3D96A5E). There is an ambiguity, but as it turns out, it can be resolved by trying both ways. If you assume the password starts with rxrp there is no valid letters to continue with. However, if you assume the password starts with rxrf, then it's possible to append a, resulting in rxrfa (12D83D3A429CD7D64E9A532C05C2C00C35032A94), which is a valid solution.

All passwords will be composed entirely out of lowercase letters. You can assume all inputs have a solution and there are no inputs that could possibly resolve to multiple passwords (for instance ["4DC7C", "A84FD", "467D7", "BD79D"] is an invalid input because it can match both "rxrf" and "rxrp").

There are no case requirements on the input. Your program is allowed to assume the input is lowercase. Your program is allowed to assume the input is uppercase.

The program must not take longer to execute than 24 hours for a 25 characters long password.

It is allowed to use external libraries or language built-in functions for computation of SHA-1 hash.

Example Input and Output

This is a JSON.

[
  {
    "input": [
      "516B9",
      "379FC",
      "19C2A",
      "9D4E1",
      "08506",
      "F808E",
      "A7F93",
      "5BAA6"
    ],
    "output": "password"
  },
  {
    "input": [
      "07C34",
      "593B7",
      "0262F",
      "CED65",
      "23612",
      "4EF76",
      "B7A87"
    ],
    "output": "letmein"
  },
  {
    "input": [
      "84A51",
      "87DDA",
      "83F67",
      "E6FB0",
      "5157D",
      "82CD7",
      "6F655",
      "43426"
    ],
    "output": "codegolf"
  },
  {
    "input": [
      "7A81A",
      "DB3D4",
      "FE05B",
      "E7280",
      "32726",
      "30AE9",
      "2C61A",
      "A9E46",
      "15D98",
      "F780A",
      "3E949",
      "F4BF2",
      "6A5C4",
      "C4554",
      "FA2EA",
      "48A40",
      "5DD7F",
      "5284E",
      "C0B8D",
      "20D59",
      "9184C",
      "32AD9"
    ],
    "output": "onetwothreefourfivesix"
  },
  {
    "input": [
      "84A51",
      "87DDA",
      "26CA7",
      "9D925",
      "08A23",
      "BE075",
      "3179A",
      "5D904",
      "54C70",
      "47790",
      "5D3B5",
      "0E4CE",
      "004C7",
      "EC8A8",
      "131A6",
      "7F47F",
      "41BC6",
      "FCF07",
      "D62BD",
      "DD14F",
      "6A141",
      "EE184",
      "595F8",
      "9D303",
      "BFD36"
    ],
    "output": "correcthorsebatterystaple"
  },
  {
    "input": [],
    "output": ""
  },
  {
    "input": [
      "4DC7C",
      "A84FD",
      "467D7",
      "BD79D",
      "12D83"
    ],
    "output": "rxrfa"
  },
  {
    "input": [
      "4DC7C",
      "A84FD",
      "467D7",
      "BD79D",
      "7B743"
    ],
    "output": "rxrpa"
  }
]

Answer 3

Posted at Baba if you, flag is win

Answer 4

Logo Pack LAPACK (Posted)

Answer 5

Migrate Try it online! to CommonMark

Try it online! generates old-style MarkDown code blocks which indent all lines with 4 spaces and then optionally precedes the block with a language comment.

Furthermore if the code block can't be parsed by old-style MarkDown (e.g. it has a leading newline, common in Retina answers), then it instead uses a <pre><code> block, with HTML escapes for all nonprinting characters.

Your program or function must take a whole TIO post, and change its code block into CommonMark style.

Examples:

# [Python 2], 16 bytes

<!-- language-all: lang-python -->

    print "Python 2"

[Try it online!][TIO-kdaf9y51]

[Python 2]: https://docs.python.org/2/
[TIO-kdaf9y51]: https://tio.run/##K6gsycjPM/r/v6AoM69EQSkAzFcwUvr/HwA "Python 2 – Try It Online"

becomes

# [Python 2], 16 bytes

``` python
print "Python 2"
```

[Try it online!][TIO-kdaf9y51]

[Python 2]: https://docs.python.org/2/
[TIO-kdaf9y51]: https://tio.run/##K6gsycjPM/r/v6AoM69EQSkAzFcwUvr/HwA "Python 2 – Try It Online"

which displays as

Python 2, 16 bytes

print "Python 2"

Try it online!

while

# [Retina 0.8.2], 13 bytes

<pre><code>
Retina 0.8.2
</code></pre>

[Try it online!][TIO-kdafdbm1]

[Retina 0.8.2]: https://github.com/m-ender/retina/wiki/The-Language/a950ad7d925ec9316e3e2fb2cf5d49fd15d23e3d
[TIO-kdafdbm1]: https://tio.run/##K0otycxL/P@fKwjMUDDQs9Az@v8fAA "Retina 0.8.2 – Try It Online"

becomes

# [Retina 0.8.2], 13 bytes

```

Retina 0.8.2
```

[Try it online!][TIO-kdafdbm1]

[Retina 0.8.2]: https://github.com/m-ender/retina/wiki/The-Language/a950ad7d925ec9316e3e2fb2cf5d49fd15d23e3d
[TIO-kdafdbm1]: https://tio.run/##K0otycxL/P@fKwjMUDDQs9Az@v8fAA "Retina 0.8.2 – Try It Online"

which displays as

Retina 0.8.2, 13 bytes

Retina 0.8.2

Try it online!

This is code-golf, so the shortest program or function that breaks no standard loopholes wins!

Answer 6

Where are the traps? code-golfnumbersequence

Related: Trapped Knight Sequence The Path Of The Wildebeest

Background ^{Partially copied from my related challenge}

The trapped knight sequence is a finite integer sequence of length 2016, starting from 1, and has the following construction rules:

1. Write a number spiral in the following manner:

17 16 15 14 13 ...
18  5  4  3 12 ...
19  6  1  2 11 ...
20  7  8  9 10 ...
21 22 23 24 25 ...

2. Place a knight on 1.
3. Move the knight to the grid with the smallest number it can go that has not been visited before, according to the rules of chess (i.e. 2 units vertically and 1 unit horizontally, or vice versa).
4. Repeat until the knight gets stuck.

It is known that the sequence ends at 2084 where the knight is trapped. But here is a twist. Suppose a knight can step back to the previous grid whenever it is stuck, and choose the grid with the next smallest number possible. By doing so, the sequence can be further extended until it is stuck again at 2720. Then, the knight steps back and choose another path, which further extends the sequence until it is stuck again at 3325...

Then, we call these numbers at which the knight is being trapped "traps". So we now know that the first few traps are at 2084, 2720, 3325, ... and it continues to infinity.

Challenge

Write a shortest program or function, receiving an integer \$N\$ as input, output the first \$N\$ traps in the extended trapped knight sequence.

Values

The first 100 terms of the sequence are as follows.

  2084,   2720,   3325,   3753,   7776,   5632,   7411,   8562,  14076,   8469, 
  9231,  22702,  14661,  21710,  21078,  25809,  27112,  24708,  19844,  26943,
 26737,  32449,  31366,  45036,  37853,  37188,  43318,  62095,  67401,  68736,
 70848,  62789,  63223,  69245,  85385,  52467,  71072,  68435,  76611,  84206,
 81869,  70277,  81475,  83776,  70767,  84763,  99029,  82609, 103815,  86102,
 93729, 100614, 108039,  82111,  99935,  85283, 109993, 119856, 119518, 116066, 
109686,  92741, 124770,  92378, 104657, 125102, 107267, 107246, 117089, 117766,
 99295, 121575,  98930, 117390, 123583, 112565, 122080, 111612, 111597,  97349,
105002, 130602, 133509, 153410, 127138, 143952, 153326, 157774, 122534, 136542,
163038, 134778, 140186, 162865, 171044, 159637, 171041, 174368, 184225, 152988

Winning Criteria

The shortest code of each language wins. Restrictions on standard loopholes apply.

Answer 7

Convert LifeOnTheEdge to LifeOnTheSlope

code-golfascii-art

Your task here is to take a LifeOnTheEdge pattern and convert it to LifeOnTheSlope.

A LifeOnTheEdge pattern is composed of these four characters: |_L . A pattern corresponds to a certain arrangement of "on" edges in a square grid. The pattern is placed in the grid first with the characters in the cells, and each of the four letters specifies the state of the edges on the left and the bottom of that cell. | means the edge on the left is on, _ means the bottom edge is on, L means both of them are on and means neither of them are on.

For example the following LifeOnTheEdge:

|_L
 |

translates to:

. . . . .
|   |
. ._._. .
  |
. . . . .

Your task is however convert it to LifeOnTheSlope. LifeOnTheSlope is a LifeOnTheEdge equivalent but only uses three symbols: /\ . You should rotate the pattern 45-degree clockwise, for example the above example translates to:

/

/\/
  \

Sandbox

I'm not sure if I described the problem clearly. Improvements on the wording and other things?

Answer 8

Identify the tonic from a key signature

Objective

Given a key signature in major, output its tonic.

Input

An integer from -14 to +14, inclusive. Its absolute value is the numbers of flats/sharps. Negative number represents flats, and positive number represents sharps. Note that theoretical keys are also considered.

Mapping

Note the use of Unicode characters ♭(U+266D; music flat sign), ♯(U+266F; music sharp sign), 𝄪(U+1D12A; musical symbol double sharp), and 𝄫(U+1D12B; musical symbol double flat).

-14 → C𝄫
-13 → G𝄫
-12 → D𝄫
-11 → A𝄫
-10 → E𝄫
-9 → B𝄫
-8 → F♭
-7 → C♭
-6 → G♭
-5 → D♭
-4 → A♭
-3 → E♭
-2 → B♭
-1 → F
0 → C
1 → G
2 → D
3 → A
4 → E
5 → B
6 → F♯
7 → C♯
8 → G♯
9 → D♯
10 → A♯
11 → E♯
12 → B♯
13 → F𝄪
14 → C𝄪

Output must be a string. Whitespaces are permitted everywhere.

Rule

• Invalid inputs fall in don't care situation.

Answer 9

Source Code Byte Frequency - Posted here

Changes from the original idea:

• Without the requirement of fixed representation of the result (percentage and trimming).
• With constraint: source code must be at least 1 byte long
• Changed from character to byte, plus removing the constraint of SBCS languages only.

Answer 10

Simulate simple Bloons Tower Defense!

For those who are unaware of this legendary series of video games, here is a link.

The task

You are going to be given an integer number and type of bloon wave and two integers describing the damage and pierce (max amount of bloons you can damage in one attack) of each attack. Your task is to output in how many attacks can you destroy the bloon wave.

Bloon types

For simplicity, there will be no special properties like fortified, regrow, camo e.t.c. White bloons will also not be present as, without special properties, they are the same as black bloons

Name - health - what it pops into
BAD   - 20000 - 3x DDT and 2x ZOMG
ZOMG - 4000  - 4x BFB
BFB   - 700   - 4x MOAB
MOAB - 200   - 4x Ceramic
DDT   - 350   - 6x Ceramic
Ceramic - 60    - 1x Rainbow
Rainbow - 1     - 2x Zebra
Zebra   - 1     - 2x Black
Black   - 1     - 2x Pink
Pink    - 1     - 1x Yellow
Yellow  - 1     - 1x Green
Green   - 1     - 1x Blue
Blue    - 1     - 1x Red
Red     - 1     - Nothing!

I/O

Input: A string describing the type of bloon, and three integers: the amount of bloons in the wave, attack damage and attack pierce

Output: An integer describing how many attacks are needed for destroying the whole wave.

Examples

Note: If there is not enough pierce n to attack the whole wave, then only the first n bloons are attacked

Input: Rainbow 3 2 10
Starting: 3x Rainbow
Attack 1: 12x Black
2: 20x Yellow 2x Black
3: 10x Blue 10x Yellow 2x Black
4: 10x Yellow 2x Black
5: 10x Blue 2x Black
6: 2x Black
7: 4x Yellow
8: 4x Blue
9: Done!
Output: 9

This is the 4/0/x Sniper Monkey:

Input: BFB 1 30 1
1: BFB(670)
2: BFB(640)
...
13: BFB(10)
14: 4x MOAB(180)
15: 1x MOAB(150) 3x MOAB(180)
...
19: 1x MOAB(30) 3x MOAB(180)
20: 4x Ceramic(60) 3x MOAB(180)
21: 1x Ceramic(30) 3x Ceramic(60) 3x MOAB(180)
22: 3x Ceramic(60) 3x MOAB(180)
...
27: 1x Ceramic(30) 3x MOAB(180)
28: 3x MOAB(180)
...
69: 1x Ceramic(30)
70: Done!

This is codegolf, so lowest byte-count wins

Answer 11

Solve the Halting Problem for Oneplis

code-golf halting-problem

Oneplis is a "very simple esolang" (I don't want to count this one toward my esolangs) made by me which only have three commands. As you can probably see from the name, it is a subset of 1+, along the lines of Befinge.

The three commands are:

• 1, which pushes 1. (Obviously!)
• +, which pops the top two numbers and pushes their sum. (Obviously!)
• #, pops a number n and jumps to the instruction after the nth (0-based) #.

Oneplis is almost certainly a (very limited) push-down automaton, since it's impossible to decrement a number and impossible to retrieve elements arbitrary deep in the stack! Oh, and the only way to read a number is with #, which cannot handle arbitrarily large numbers!

This is code-golf, so shortest code wins! Your output should be truthy for halting, and falsy for non-halting. You can use any set of five characters for the instructions. Don't care if it jumps to a non-existence # or trying to execute + when there are <2 numbers on the stack.

Test cases

11+ -> True
1##1# -> False
1## -> True
11+1+###11+# -> True
11+##1#1 -> False

Sandbox

• Test cases?

• Shall I require the answers to deal with errors?

Answer 12

Noncommutative Quineoid Triple

This is the hard mode of Quineoid Triple

Write three different programs such that all of the following properties hold:

• \$ A(B) = C \$
• \$ B(C) = A \$
• \$ C(A) = B \$
• \$ A(C) = -B \$
• \$ B(A) = -C \$
• \$ C(B) = -A \$
• \$ A(A) = \epsilon \$
• \$ B(B) = \epsilon \$
• \$ C(C) = \epsilon \$

Where:

• \$ f(g) \$ is the output obtained from feeding the program text of \$g\$ into program \$f\$
• \$ -x \$ is the program text of \$x\$ in reverse (reversed in terms of either raw bytes or unicode codepoints)
• \$ \epsilon \$ is the empty string / an empty output

Rules and Scoring

• This is code-golf, so the shortest program length total, in bytes wins.
• Standard quine rules apply.
• Each program can be in any language. Any number of them may share languages or each may use a different language.
• Use any convenient IO format as long as each program uses a consistent convention.
  • Functions are allowed, as this counts as "any convenient IO".
• The result of feeding anything other than program text of one of the three programs is undefined.

Answer 13

Sandbox note: This is partially inspired by There's a fault in my vault!, which I thought had some interesting ideas in it. This is my effort to frame those ideas in a clearer fashion.

---

Cops/Robbers: Create a weak block cipher

cops-and-robberscryptography

In cryptography, we often use block ciphers, which are a form of keyed encryption. More specifically, for a plain text string \$s\$ and a secret key \$k\$, we design an encryption function \$E(s, k)\$ and a decryption function \$D(\hat{s}, k)\$ such that if we encrypt and then decrypt the text with the same key, we get back our original text. That is, we have \$D(E(s,k),k) = s\$ for all possible strings \$s\$ and \$k\$.

One security property a good block cipher has is that it is resistant against key-recovery attacks. This means that if we have the ability to run \$E(s, k)\$ and \$D(\hat{s}, k)\$ for various choices of \$s\$ and \$\hat{s}\$ and collect pairs of encrypted and decrypted text we cannot tell what the key is.

In this challenge, you will design a simple block cipher that is intentionally vulnerable to a key recovery attack, and challenge others to try and exploit it.

The Cops' Challenge

1. Design a block cipher. Design an encryption function \$E(s,K)\$ and decryption function \$D(\hat{s},k)\$ that take strings (or your language's closest equivalent) of a fixed length \$16\$ bytes and a key of fixed length \$16\$ bytes and outputs a string of length \$16\$ bytes. Your \$E\$ and \$D\$ functions must have the property that \$D(E(s,k),k) = s\$ for all 16-byte strings \$s\$ and \$k\$.¹ The functions must be deterministic (not use any randomness) and pure (not rely on any outside state). Your \$E\$ and \$D\$ must work within the integer/float precision of your language. Specifically, you may not treat floating point as if it's arbitrary precision, nor may you assume integers of arbitrary size if your language utilizes fixed-size integers.
2. Implement a secret key-recovery attack on your block cipher. Write a program that makes calls to \$E\$ and \$D\$ for a secret, unknown key \$k\$ and fully recovers the key by observing properties of the input/output pairs. The key must be recovered with probability \$1\$ - you may not rely on probabilistic approaches.² You must treat \$E\$ and \$D\$ as black boxes, from which you can only observe their input and output. This means you must not utilize runtime introspection, timing information, or other side effects of the implementation. You must only pass full \$16\$ byte strings to \$E\$ and \$D\$, and not any other type. This means you may not rely on special objects with overloaded operators or similar to glean information about how the input is processed by \$E\$ and \$D\$. Your attack may be adaptive, in that it decides which strings to pass in based on outputs to previous strings. To enforce a practicality limit, your attack must work for a combined total of strictly less than \$2^{16}\ = 65536\$ calls to \$E\$ and \$D\$ for any key \$k\$. If the block cipher you design has the property that for keys \$k_1\$ and \$k_2\$ that \$E(s,k_1)=E(s,k_2)\$ and \$D(s,k_1)=D(s,k_2)\$ for all \$s\$, then we call these keys functionally identical, and your attack may recover any functionally identical key to the original.

That's it! You will reveal both the encryption and decryption functions \$E\$ and \$D\$, and challenge the robbers to find your key recovery attack (or possibly a different one).

Clearly, the challenge is to design your \$E\$ and \$D\$ to look secure, but they have some catastrophic weakness that allow you to recover the key with very few calls. Another approach is to 'trapdoor' the function in some way only known to you. In the spirit of Kerckhoffs's principle, you are encouraged to post a short explanation of what your \$E\$ and \$D\$ do, especially if they are written in an esoteric language.

You may use cryptographic functions if you wish, but using them presents several practical problems. Hashing functions are designed to be one way and your are unlikely to be able to design both an encryption and decryption function that utilizes them. Symmetric ciphers have both encryption and decryption, but is unlikely to allow the key recovery attack outlined here.

If no-one mounts a successful attack in 7 days, you may post your key recovery attack and mark your answer as safe, which prevents it from being cracked. Note your submission can still be cracked until your reveal your attack.

Your answer is invalid if you do not follow the rules set above. Your answer can be declared invalid even after it is marked safe, if it turns out your revealed attack does not obey the rules.

The shortest safe submission, calculated as the sum of the bytes of the two functions \$E\$ and \$D\$, wins. Your functions must be named.

The Robbers' Challenge

1. Find a vulnerable answer. That is an answer, which hasn't been cracked yet and which isn't safe.
2. Crack it by designing a key recovery attack. Your attack must follow the rules outlined in the cops section. To recap, this means:
   • The total number of calls to \$E\$ and \$D\$ with the key \$k\$ must be strictly less than \$2^{16}\$
   • You must only pass \$16\$ byte strings to \$E\$ and \$D\$, and must have the key \$k\$ initially be unknown
   • The attack may be adaptive but must work to recover any 16 byte key \$k\$ (or a functionally identical key)
   • You must treat \$E\$ and \$D\$ as black box, and may not use runtime introspection, timing information, etc.

If you've found such a attack, post an attack on the robber's thread linking back to the answer. If possible, you should post a link to an online interpreter which allows others to run your attack for various keys \$k\$. You are encouraged to post how your answer works, and the maximum number of calls your approach makes to \$E\$ and \$D\$. If your attack does not recover the key, but instead a functionally identical one, explain (briefly) why they are functionally identical.

You must not crack your own answer.

The user who cracked the largest number of answers wins the robbers' challenge. Ties are broken by the sum of bytes of cracked answers (more is better).

Example #1

Python 3, 133 bytes (cop)

E=lambda s,k:''.join(chr((ord(c)+ord(d))%256) for c,d in zip(s,k))
D=lambda s,k:''.join(chr((ord(c)-ord(d))%256) for c,d in zip(s,k))

Try it online!

My program computes the sum of \$s_i\$ and \$k_i\$ for each \$i\$.

Python 3, cracks xxx's answer

leaked_key = E('\0'*16,k)
print('key = %s' % leaked_key)

Try it online!

My crack completes in \$1\$ call and uses that fact that \$0 + k = k\$.

Example #2

Python 3, 147 bytes (cop)

def E(s,k):
 o=''
 V=[*range(256)]
 j=0
 for i in range(16):
  j+=V[i]+ord(k[0])
  j%=256
  V[i],V[j]=V[j],V[i]
  o+=chr(ord(s[i])^j)
 return o
D=E

Try it online!

My program uses a complicated thing.

Python 3, cracks yyy's answer

leaked_key = ''
for c in range(256):
 if E('f'*16,chr(c))==E('f'*16,k):
  leaked_key = chr(c)+'x'*15
  break

print('key = %s' % leaked_key)
assert E('abcdabcdabcdabcd', leaked_key) == E('abcdabcdabcdabcd', k)
assert D('abcdabcdabcdabcd', leaked_key) == D('abcdabcdabcdabcd', k)

Try it online!

They only ever use the first byte of the key, so we can just bruteforce the first byte and pad with anything to get a functionally identical key. This involves a maximum of \$256\$ calls to \$E\$ with the secret key.

---

<sup>1. This means that if your language uses null-terminated strings, such as C, then you should be using memcpy-type operations instead of string operations. Since the input length is fixed as 16 bytes, this should be no issue.
2. This requirement forbids most kinds of Birthday attack.</sup>

---

Questions to sandbox users:

• I know this is a lot to take in. Is it clear?
• Can anyone think of a trivial way to trapdoor \$E\$ and \$D\$ with eg. a hashing function? I don't think it's possible, but I could be wrong.

Answer 14

Take 6!

A good card game is a wonderful thing. I got me a nice fresh set of Take 6! Too bad though, I have no-one to play with. And so I turn to you!

The Game

The game is played with a set of 104 cards, numbered 1 to 104 inclusively. Each card has a number of 'cows' attached. Here's a quick Python function to calculate the number of cows:

def cows(card):
    out = 1
    if(card % 5) == 0:
        out += 1
    if(card % 10) == 0:
        out += 1
    if(card % 11) == 0:
        out += 4
        if(card % 5) == 0:  # C-c-c-combo
            out += 1
    return out

Therefore, there is a total of

• 1 card with 7 cows (number 55)

• 8 cards with 5 cows (the other multiples of 11: 11, 22, 33, 44, 66, 77, 88, 99)

• 10 cards with 3 cows (multiples of ten: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100)

• 9 cards with 2 cows (other multiples of five: 5, 15, 25, 35, 45, 65, 75, 85, 95)

• 76 cards with 1 cow (all other cards)

The game is played by up to 10 players.

Each player is given 10 cards. 4 cards are placed on the table as the starts of 'rows'. Then 10 turns of play take place. Then, results are calculated.

A turn

Each player selects one of their remaining cards. At the same time, they reveal their selected cards.

Going in the order of lowest card number, the player whose card it is must place it into a row according to rules:

1. If there is a row with the top card of a lower number than the player's and no such row with a lower number exists, their card must be placed at the end of the row. If their card is the sixth in a row, they take the first 5 cards and put them on their result pile, leaving theirs as the new start.

2. If no such row exists, they must pick one of the rows, take all the cards there to their result pile, and leave their card as the new start.

Examples:

row tops: 10 20 30 40

played: 25

must be placed on the row with a 20, creating the configuration 10 25 30 40 with a possible cow gain

row tops: 10 20 30 40

played: 9

pick any row, creating for example 10 20 9 40, but guaranteed to gain cows

Counting

The sum of cow values of the cards in a player's result pile is their score. The lower the score the better.

Scores may be added up over several games, creating an overall score for a match.

Bots

Bots will be standalone programs. Everything belonging to a bot will be placed in a single directory, the name of the directory will be used as the name of the bot. A launch script named launch (may be the entire bot) must be provided. If necessary, a compilation script named build may be provided. Both scripts shall be placed directly in the bot's directory and should use shebangs to specify how they are to be run.

Bots shall not interfere with other bots, the controller, or the git repositories used.

The bots will have the option of storing extra information in files in their own directory. It will be wiped when a fresh series is being run (such as after adding a new bot).

An override input format may be provided. I intend to use StringTemplate for this, I'll write up some details when working on the controller. The default format will have all messages newline-terminated.

Once launched, the bot will be first given their cards, as a list of card numbers, where the numbers may or may not be ordered.

The default format will be

cards 0 1 2 3 4 5 6 7 8 9

No response is expected.

For each round, the bot will be prompted with the current state of the grid, that is the number of cards in each row, the sum of cows in each row and the top number card in the row.

The default format will be

count 1 2 3 4

cows 5 6 7 8

top 11 20 22 35

The bot shall answer with the number of one of its remaining cards.

The list of all the cards used by all bots in the round will be given to each bot. Not that this includes the bot's own card. The order of bots in this message will be consistent within a game.

The default format will be

used 0 1 2 3 4 5 6 7 8 9

No response is expected.

If the placement rule 2. has to be invoked, the bot will receive a message containing the board state at the time when it needs to pick a row

The default format will be

pickrow

count 1 2 3 4

cows 5 6 7 8

top 11 20 22 35

The bot shall respond with the number of the row it wishes to take. The rows will be 0-indexed for this.

If the bot's move results in a gain of result cows, it will be informed of which cards and how many cows it has gained (note that the lower the number the better).

The default format will be

cardgain 1 2 3 4 5

cowgain 6

No response is expected.

At the end, all bots will be shown their score as well as all the scores of others, in the order consistent with the used cards message.

The default format will be

score 30

others 0 1 2 3 4 5 6 7 8

No response is expected.

If the bot makes an invalid move, it will be delivered a special message informing it of such. From that point the bot's current game is over. It gets 100 points of penalty.

The default format will be

invalid

A timely shutdown is expected.

The bot may of course try to save information to its private file at any time, including at the end.

After the final message, the bot shall terminate in a timely manner.

Scoring will be added up over many games, number depends on how fast the games end up running, but at least 100 sounds reasonable to me.

Bots will be placed in a separate github repository TODO for easy setup and reseting. Bots that need a compilation script but don't have one will be given one.

Controler

Work has started at https://github.com/MrRedstoner/Take6KOTH

The controller will be designed to run in Java 1.8+, using the Process API to launch bots.

Notes:

While the number of bots is too low, it will be padded to 10 by using multiples of primitive bots. The tournament style once 11+ submissions exist is for now playing all subsets of size 10.

I intend to write up at least a few primitive bots, to get the games going. Something like using cards in the order they were given, or randomly. These will also demonstrate the custom input functionality. Maybe even one that uses external input, to let me play for fun!

Limits for execution time, storage of data etc. are not given at this time. If bots start to behave excessively limits may be added.

Sandbox notes:

Any better idea for tournament?

Should bots be given the names of their competitors as well? Currently leaning towards yes.

Planned tags: king-of-the-hill

Answer 15

Output all of printable ASCII using all of printable ASCII

Posted

Answer 16

Count the Collatz survivors mod 2^n code-golfnumbernumber-theory

Answer 17

Round a Matrix

Your input is a 2d array of nonnegative floats A. It can be supplied in whatever format is most acceptable for your language. It can have any dimensions.

Let r and c be the 1d arrays of row and column sums of A respectively, rounded to the nearest integer, with the rule that 0.5 is rounded up to 1.

Your task is to output a 2d array of nonnegative integers B such that |b_{ij} - a_{ij}| < 1 for all i and j, and also the row and column sums of B are equal to r and c respectively.

In other words, B is obtained by rounding each element of A up or down, in such a way that the row and column sums are preserved.

There may be many possible solutions. In this case, you only need to output one of them.

If there is no solution, your program's behaviour can be undefined.

Example:

 A = 1.2 3.4 2.4
     3.9 4.0 2.1
     7.9 1.6 0.6

in this case, the row sums are [7.0, 10.0, 10.1] and the column sums are [13.0, 9.0, 5.1] so after rounding these, you get r = [7 10 10] and c = [13 9 5]. One acceptable solution is

 B = 1   3   3
     4   4   2
     8   2   0

This is code golf, so the shortest code wins.

Motivation

I am also interested in what clever algorithms people can come up with. I guess the most obvious is just to do a random search, but that can take a very long time, even if the array is only 10x10 or so.

Questions

• Is it clear? Please can you edit it if it's not in the right format?
• Has it appeared here before? (I don't think so, because I was searching Stackoverflow for a while in order to come up with a solution to this.)
• Is there always a solution under the conditions given here?
• Would it be better in some other format than code golf?
• Should the condition |b_{ij} - a_{ij}| < 1 be |b_{ij} - a_{ij}| <= 1?

Answer 18

The Fibonacci Rectangular Prism Sequence (posted)

Answer 19

I only want some primes, not all of them

It is well known that there are various formulae for calculating primes that span from calculating a subset of primes, to all possible primes. However, for this challenge, I only want a specific subset.

You are to write a program which takes a single natural integer \$n>0\$ as input. This program will then output a function, \$f(p)\$, which will take a integer \$p\ge0\$ and do the following:

• If \$p < n\$, return the \$p\$th value of a contiguous subset length \$n\$ of primes
• If \$p \ge n\$, returns a non-prime integer (including \$0\$, \$1\$ and negative integers).

For example, Euler's quadratic \$p^2+p+41\$ returns the \$p\$th value of the subset of primes \$\{41, 43, 47, ..., 1601\}\$ for \$0 \le p \le 39\$. However, for \$p=43\$, this returns \$1933\$, which is prime, so this would not be a valid function to return for \$n = 40\$.

You may choose the subset (and it may differ for different \$n\$), so long as it is finite and contiguous. You may also choose to use 1-indexing for \$p\$, meaning that \$f(p)\$ returns primes for \$1 \le p \le n\$.

You may output in the most natural form of a function in your language. For example, Jelly would return a string representing a link, Python would return a named function or lambda etc.

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

---

Meta

• Thoughts and feedback?
• Is this a duplicate?
• Tags are code-golf, primes, functional-programming. Any others?

Answer 20

Question has been posted

Answer 21

Middle-Square RNG: What Number Came Before? (WIP)

A well-known, but statistically poor, way of generating random numbers is to square the number and take the middle digits (when expressed in base 10)

Your task is to take a 4-digit number as input and output any 4-digit number that produces the input number (there may be more than one, which is one of the statistical flaws of this method) when applying middle-square. If the square has an odd number of digits, take an extra digit off the left side.

If there is no such number (some numbers with this method have no predecessor- yet another statistical flaw), indicate that clearly in a way that cannot be mistaken as a valid answer. Some possible ways of indicating this:

• Output nothing
• Output null/None/nil/false
• Output an empty list
• Output a negative number
• Output an error message that is clearly not a 4-digit number
• Throw an exception
• Crash
• Exit with a nonzero status

code-golf random

Answer 22

Operational countdown

code-golf

• Posted.

Answer 23

A Snake, A Camel And A Kebab.

As many of you will know, almost every programming language has a standard casing system; unfortunately, we have not been able to agree on a singular system to use and now must frequently switch between camelCase, snake_case and kebab-case.

Now I know what you're thinking... wouldn't it be nice if we had a program that could convert from one casing to another?
Well - soon we're going to have plenty!!! (This is where you come in)

Challenge

You're job is to write a program/function that will take an input string, and a casing system. It will then print/return the converted string.

Inputs:

You're program will receive two inputs, an alphabetic string that is to be converted and a string that will always be one of kebab camel or snake.

Outputs:

You're program should output a string that conforms to the new casing if it is possible. If the input string was invalid, and had mixed casing, you're program should print/do nothing.

Test Cases:

Valid Examples:
"aJavaVariable", "snake" = "a_java_variable"
"a_python_variable", "kebab" = "a-python-variable"
"golf", "camel" = "golf"
"", "snake" = ""
"doHTMLRequest", "kebab" = "do-h-t-m-l-request"

Invalid Examples (no output):
"an_InvalidName", "kebab"
"invalid-inPut_bad", "camel"

Additional Info:

• As most programming languages prefer lowercase variable names, you should convert all letters to lowercase unless it is needed to be upper case for camel casing.

---

Meta

• Is this a duplicate? I couldn't find any quite like it.
• Are the rules clear?
• Would it lead to more creative answers if I remove the possibility of being given invalid input, and assume all input will be valid?

Answer 24

How Many Atoms?

code-golfchemistryparsingstring

Post

Answer 25

Based Palindromes

Answer 26

Partial sums of the kempner series code-golf math sequence

Posted

Answer 27

Eye test - How many squares are in this picture?

Answer 28

Run the lottery

Rules

Your job is to write a program to accept lottery tickets, adding all the money to a pool, and divvy out the winnings based on how many numbers each ticket has guessed correctly. The amount of money people spent on their tickets is used to determine how much each person should take home.

1. You will receive a list of lottery tickets, which will be how much the person has paid, along with 5 numbers between 1 and 25. The numbers do not have to be unique, and order matters. [1, 2, 3, 4, 5] and [3, 2, 1, 4, 5] are considered different, and [1, 1, 1, 1, 1] is a valid ticket.
2. You will also receive 5 numbers between 1 and 25, which are the winning numbers. This follows the same restrictions as a participant's ticket.
3. Each participant will be given a "score" based on how many numbers they guessed correctly. They must guess the number, and guess it in the correct spot as well. [x, x, 1, x, x] is not a winning number for [1, 2, 3, 4, 5]. [1, 1, 1, 2, 3] counts as 2 correct guesses for [1, 2, 1, 1, 1].
4. The score is \$4^n\$ where \$n\$ is the number of winning numbers. Yes, a participant with 0 correct numbers has a score of 1, and is eligible to take home some money.
5. Each participant's final weight is their score times the amount they spent on the ticket. A person with a score of 4 (1 correct guess) and paid $4 for a ticket has the same weight as a person with a score of 16 (2 correct guesses) and paid $1 for their ticket.
6. Finally, the prize pool is then divvied up. 10% goes to you, the lottery company. The remaining 90% gets divvied up proportionally by each participant's final weight, rounded to the cent.

The input and output of the program can be in any format. The only stipulation is that monetary values must be decimals. For instance, $15.68 cannot be represented as 1568.

Example game

The winning numbers are as follows

• [2, 18, 1, 15, 7]

Four people bought tickets with the following prices and numbers

• $6, [9, 5, 6, 15, 22], one match, score of 4, weight of 24
• $2, [2, 25, 17, 7, 7], two matches, score of 16, weight of 32. Notice how only the second 7 counts, order matters
• $67, [11, 16, 9, 20, 16], no matches, score of 1, weight of 67
• $1, [12, 19, 6, 25, 2], no matches because the 2 is in the wrong spot, score of 1, weight of 1

The total pool is $76, $68.4 after we take our cut, which is then sent out based on the weights. The sum of all weights is 124.

• First ticket gets 24/124, $13.24
• Second ticket gets 32/124, $17.65
• Third ticket gets 67/124, $36.96
• Fourth ticket gets 1/124, a whole 55 cents

Answer 29

Is each bracket matched?

code-golfdecision-problembalanced-string

Given a string consisting only of the characters ()[]{}, determine if each type of bracket is matched--that is, every ( corresponds to one later ), every [ corresponds to one later ], and every { corresponds to one later } (and vice-versa).

Pairs are allowed to overlap: ([)] is just as valid as ([]).

Output one consistent value for one classification and anything else for the other, or following your language's truthiness semantics (inverted if you want).

Test cases:

Matched:

()
[]
{}
()[]{}
()()([])
{[][}]
{{{}}}
([{}]){([]})
[(()())(((())))(]()(()))

Not matched:

(
]
{{}
[)
(()())((((()))))(()()(())(())))
{}{}{)
[())[])]
)(

Meta

• Does this admit a variety of interesting solutions?
• Would it be better to add <> as a bracket type? Have fewer bracket types? Arbitrarily many?
• I'm writing this up entirely because I'm surprised it hasn't been asked yet, so although I have looked, this might still be a duplicate.
• Although I don't think it's necessarily unclear, I feel like the specification could be worded better.

Answer 30

Count strictly overlapping substrings code-golf string counting subsequence

Posted