Restricted mini challenges Cop's Thread

Question

Robber's thread

Your task as cops is to select three things:

• A programming language

• An OEIS sequence

• A byte set

You are then to secretly write a program in that language that computes the nth term sequence using only the bytes in the set. You will reveal the three pieces of information so that robbers can try to figure out the program.

Answers will be scored by the number of bytes in the byte set with more score being good. Cracked answers have an automatic score of 0. If your answer is uncracked after one week you may reveal the intended program and mark your answer as "safe".

Answers must be capable of calculating every term in the b-files of the sequence, but are not required to calculate any terms after.

Sequences can be either 1 or 0 indexed for both cops and robbers.

Here is a Python Script that checks if your code matches the given byte set.

Answer 1

C, A027868 (Cracked)

I don't expect this to last too long...

Byte set: int (){reu<5?-:/;}

Answer 2

R, A057077, (cracked)

1, 1, -1, -1, 1, 1, -1, -1, etc

Byte set:

()*/=2abcinopst

0-indexed.

Answer 3

JavaScript (ES6), A000035, cracked

A000035 is n mod 2, in case the site goes down or you're too lazy to check yourself. Charset:

023456789\`efu

Taking the "somehow still Turing-complete" route. I suppose I could've added 51 or so non-ASCII chars to improve my score, but that feels kind of like cheating.

Takes input through prompt and outputs through alert, and can be run in any modern browser.

---

Intended solution:

\u0046\u0075\u006e\u0063\u0074\u0069\u006f\u006e`\u0046\u0075\u006e\u0063\u0074\u0069\u006f\u006e\u0028\u0046\u0075\u006e\u0063\u0074\u0069\u006f\u006e\u0028\u0022\u0072\u0065\u0074\u0075\u0072\u006e\u0028\u0034\u0038\u0032\u002f\u0032\u0029\u002e\u0074\u006f\u0053\u0074\u0072\u0069\u006e\u0067\u0028\u0032\u0032\u0029\\u002\u0062\u0027\u0065\u0072\u0074\u0028\u0070\u0072\u006f\\u006\u0064\u0070\u0074\u0028\u0029\u0025\u0032\u0029\u0027\u0022\u0029\u0028\u0029\u0029\u0028\u0029```

which, when the escapes are removed, translates to

Function`Function(Function("return(482/2).toString(22)\u002b'ert(pro\u006dpt()%2)'")())()```

which simplifies again to

Function`Function(Function("return(482/2).toString(22)+'ert(prompt()%2)'")())()```

This works because JavaScript allows \uXXXX escapes in variable names (though not in arbitrary code, as Java does). The outer Function`code``` is necessary to run the code at all, since the entire thing needs to be escaped.

(If you're confused about how this works: JavaScript has something called tagged template literals, which for our purposes is just a function call on a string; it just uses f`string` instead of f("code"). So Function`code``` is about the same as Function("code")().)

Now, because of the lack of the hexadecimal chars 1abcd, we'll have to double-encode certain necessary characters such as the m in prompt(). So instead of \u006d, it becomes \\u006\u0064. But now we need to evaluate this as a string twice to make sure this gets fully decoded. (pro\u006dpt() would work just fine, but using \u002b as + would not.) This is what the second Function(code)() is for.

One further obstacle exists: there's no 1 in the charset, necessary to create an a from \u0061. So there's no way to generate an a by unescaping a string (I checked, the octal representation is \141). Instead, we can generate it with e.g. (20/2).toString(20). I went ahead and generated al in this manner because l would require double-escaping like m.

But the problem now is that the innermost Function call is now just generating a string. In order to actually execute it, we need to return it from the function and pass it to a third Function call. This we do, and finally our journey is complete.

^{*I am aware of using ${} within template literals, but those aren't in the charset, alright?}

Answer 4

PowerShell, A000012, 19 bytes, SAFE

$.0=[]acefilnorstv

Includes a newline and 18 other bytes. Good luck.

Try it online!

---

Intended Solution:

$a=$a[0]
$error[0].invocationinfo.offsetinline

Try it online!

This sets $a to be the value of an uninitialized variable $a indexed at [0]. Since that won't work, you get an error stating the following:

Cannot index into a null array.
At line:1 char:1
+ $a=$a[0]
+ ~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : NullArray

The second line then pulls the .InvocationInfo and .OffsetInLine (i.e., where the error occurred), which in this case is always 1, and hence the A000012 sequence.

Answer 5

CPython 3.6.2, A000002 (cracked)

I don't want anybody running out of single-character variables, so I'm giving you 70 pseudo-random characters courtesy of Latin-1.

·èõÉÀ]ýÜâô¾×l¡¿Ós¦Í½²uÊi´#¬©Åñ[);?ò
à¢ådêøóÎÐþÒÏ®,(Öß.=Õc_ö\§éºún$tÞb¨

This is evil. You can't make a for loop. You can't make a while loop. You can't even try to do anything, much less except. I have given a new line so that you can use more than one statement, but there aren't any spaces, tabs or even colons to let you use any sort of flow control. There are no numbers. There are no strings. There is nothing of any use.

You do have \ and #, though, so you can write clear code with soft breaks and comments.

That is, if you speak Jelly.

Answer 6

Python 2, A000142, cracked

Probably not too difficult, but since I really enjoyed solving these I thought I'll be a cop for once. Here's the byteset (first one is a space):

 ()*-:=abcdfghijklmoqruwyzABCDEFGHIJKLMNOPQRSTUVWXYZ

Intended solution

LyricLy's solution is much cleaner, but here's the one I had in mind:

Basically it's the same but instead of using bool(r) for 1 I used (r-r)**(r-r): f = lambda r: (r==r-r or r==(r-r)**(r-r))*(r-r)**(r-r) or r*blam(r-(r-r)**(r-r))

Answer 7

Cubically, A016742 (Cracked)

This sequence is even square numbers: 0, 4, 16, 36, 64, ...

Byte set:

• Any letter except [UuDdLlRrFfBb]
• The digits [6789]
• Any symbol except [-^:@/]
• Anything not mentioned in the ASCII character set, including whitespace.

Try It Online!

Answer 8

Braingolf, A010701 Score: 9 [SAFE]

Byte set:

0x21, 0x24, 0x2F, 0x3A, 0x3F, 0x5B, 0x5D, 0x5F, 0x7C

Try it Online!

The code:

$_/[!?:]|[!?:]|

Try it online!

Explanation

$_/[!?:]|[!?:]|  Implicit input from commandline args
$_               Remove top of stack
  /              Niladic division, push 5
   [...]         While loop, decrements bottom of stack at start of loop
                 then decrements each time loop reaches end
                 Exits when bottom of stack is 0
    !?:.|        If conditional without popping, runs contained code if top of stack is 0
                 This is the sneaky trick here. The conditional skips the end of the loop
                 As a result, this whole block from [ to | effectively acts as a decrement.
         [!?:]|  We do this twice to lower the 5 we pushed down to 3
                 Implicit output of top of stack.

Answer 9

Python 3, A000002, Cracked with the intended solution

These are the bytes of a full program, 0-indexed solution for the Kolakoski sequence: OEIS A000002.

pg*rn:e+%2a tu]
(=foi[)1l,

This contains a space, a newline, and all the other characters in the snippet above. Hopefully this won't be too easy to crack :)

Answer 10

Python 2, A000042, 11 Bytes (Cracked)

Byte set:

int(pru*1)'

Answer:

print '1'*input()

Note: This is my first ever answer on PPCG, and I may have made a mistake...

Answer 11

JavaScript (ES6), 4 bytes, A005408 (Cracked)

This should be an easy one. Odd numbers: a(n) = 2n+1

Byte set:

$+=>

Answer 12

Python 2, A001146, Cracked

Byte set:

print(2*u)

Answer 13

LOLCODE, A000290, Cracked

Byte set:

.12ABDEFGHIKLMNOPRSTUVXY

The byte set also includes space and newline.

HAS FUNZ!

Answer 14

CJam, A000142, 8 bytes, Cracked

Byteset: {}*+)%1\

Answer 15

Unreadable, A000027, 92 bytes, Cracked

Byte Set:

!"#%&'()*+,-./0123456789:;?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~

Also add space and newline

Answer 16

Octave, A000045

This produces the Fibonacci numbers, OEIS A000045. There's both a space and a newline in there.

It's 0-indexed, so input 0 gives 0.

 ()-;=>cdefinotu

Answer 17

JavaScript, A000004 (Cracked)

Look from the other side

at~N+1

Step Hen's solution

~NaN+1

My solution #1

~1+1+1

#2

~~NaN

Answer 18

Python 2, A006577, Cracked

Byte set:

+s-t,n u
r)i1(d>]f[:e&

Shouldn't be too hard, but still fun.

EDIT: Cracked by @BruceForte. The crack looks just about identical to my crack, but here's mine for reference.

Try it Online

Answer 19

dc, A028444 (cracked)

-?/*+23568dpr

There are no spaces in the byte set, but that’s not a big deal for dc.

Sequence is indexed at 0.

Note: Rado’s Sigma function grows faster than any computable function and is thus noncomputable!

Intended solution: ?dddddd***3*rdd**22*-rd*53*+r26*-8/p

Answer 20

Ly, A005150, Cracked

!$+-012<=>JS[]lnprsu

Well. Let's see how this plays out.

Answer 21

Perl 5, A007094 (Cracked)

Numbers in base 8

Byte set sub {if($_[1]!=%/)ret-n;}

Try it online!

Answer 22

shortC, A000240, 64 bytes

Uses the characters in this ASCII map:

    "     %     ( ) * + , -     
  1 2                       >   
@ A         F     I             
    R   T             [   ]     
  a     d         i         n o 
p       t     w       {   }    

Map credit: ETHproductions

Answer 23

CPython 3.6.2, A000796 (cracked)

I like Latin-1. Here's another 70 characters.

,Ðûô[u÷ÎÆ»énb¤Äö]?có´å¡ùÇõÓ«;Ñ$èñÙdÁ¼
¢üÔltsð½(þÚ#ä.×çÈýŧã¯\)³íï¬Â±¥_Ê=iÌ

This bunch of characters can calculate the decimal digits of pi. Surely this requires flow control. And yet there isn't a colon, so that is impossible. You can't even eval a string when there is neither eval nor a string.

I'll give a hint: my program takes input from stdin and outputs to stdout, but I am almost completely certain that it is possible to use other I/O methods.

Answer 24

cQuents, A033307, Safe

Fe_pz:"/`'-2;

Try it online!

Explanation:

":z--F_p-2
Try it online! ": means a char sequence; basically, the output needed. Now, we need to just get the current index, which would usually be $. z starts out as 0 and is the previous number from then on, so we need just to add one to it. -- is the equivalent of +, and F_p-2 means Floor(Pi-2), which works.

Answer 25

Perl 5 -n, A000290: the squares, score:18, safe.

 ;cdeghijklnopqrst

Rules

• Input from stdin, as a string of decimal integer.

Intended solution

int or print;int or die;int ne length q q q or print;int ne length q q q or die;s ss s;chr sqrt length eq chr or redo;print length

Try it online!

Usage: from stdin, as a decimal integer. 0-indexed. Can accept only a line. Input shall match /^\d+$/. No trailing LF to your input. Output from stdin, as decimal integers. If your input is 0 or 1, the program dies but please don't care for such thing; this specification is just for this challenge.

Answer 26

R, A000027 (Cracked)

An easy one to warm up :)

Byteset:

eiytnd

Solution:

identity returns the input, so maps n to n.

Answer 27

Python 2, 24 bytes, A001246, cracked

Byte set:

 )(+*-/12:=<acbdfmlonrx

Try it online!

Answer 28

Python 2, 21 bytes, A157433, cracked

6ut1 28rp5=)ni+03(*7

Try it online!

Original solution:

n=input() print 128*n**2+2336*n+10657

Probably super easy, but eh, I have =).

Answer 29

Jelly, 16 bytes, A000042 (Cracked)

Byte Set:

%1@JOiv¤ØȷḌṁị“”€

(The two quotes are different: one is opening and the other is closing).

(uses Jelly codepage)

The sequence is: a(n) is the unary representation of n.

Answer 30

Python 3, 19 byteset, A000290, Cracked

This is the perfect squares: 0, 1, 4, 9, ....

Byteset:

(fam, l+db-ise=10:)

Note: I had two iterations with duplicate characters (and missing characters) because I'm dumb.

My solution (not very efficient):

f=lambda l,a=1,b=0:f(l-1,a+1+1,b+a) if l else b

Try it online!