Cops: Make a regex - Make a snake

Question

This is the cop's thread. The robber's thread is here.

---

Write a code that takes an input n and creates a n-by-n "snake matrix".

A snake matrix is a matrix that follows this pattern:

3-by-3:

1  2  3
6  5  4
7  8  9

and 4-by-4:

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

The exact output format is optional. You may for instance output [[1 2 3],[6 5 4],[7 8 9]], or something similar.

You must provide the language name, and a regex that fully matches your code. You can choose how detailed your regex should be. In the extreme, you can write a regex that matches every possible string, in which case it will be very easy to crack your code. You must also provide the output for n=4, so that robbers know the exact format you have opted for.

You may use one of the regex-flavors that are available on regex101.com, or the Ruby flavor.

• PCRE (PHP)
• Javascript
• Python
• Golang
• Ruby

You must specify which one you are using.

Notes:

• You must support any reasonably large n. You may assume it won't overflow the datatype or memory. If the default datatype is 8-bit signed integers, then you can assume n<=11, if it's unsigned 8-bit integers, then you can assume n<=15.
• The robbers have to match the submission's output format, except leading/trailing spaces and newlines, since that might have been stripped away by the SE formatting.

Winning criterion:

The winner will be the uncracked submission with the shortest regex, measured in number of characters.

If your post has remained uncracked for 7 days, then you may post the intended solution and mark your submission as safe.

Answer 1

05AB1E, Cracked by mbomb007

Hopefully fun to crack and not too obvious.

Regex (PCRE):

^\w*[+\-*\/%]*\w*.{0,2}$

Output n=4:

[[1, 2, 3, 4], [8, 7, 6, 5], [9, 10, 11, 12], [16, 15, 14, 13]]

Original solution

UXFXLNX*+NFR}ˆ

Answer 2

Python 2, length 62, cracked

Regex (PCRE)

^while ((?=\S)[1di\W]|an|eval|nput|nt|or|pr){55}s(?1){45}n...$

Sample output

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

Answer 3

Jelly, length 6, cracked

Regex (PCRE)

^.{9}$

Sample output

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

Answer 4

R, length 14 Cracked by plannapus

I hope I got this regex right. What I trying to say is 77 characters excluding <space>, #, ; and [. I tested it here

Regex

^[^ #;\[]{77}$

Sample output n= 4

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

Answer 5

05AB1E, Cracked by Value Ink

Lets kick it up a notch :)
Hopefully a nice puzzle.

Regex (PCRE)

^\w*..\w*$

Output n=4

[[1, 2, 3, 4], [8, 7, 6, 5], [9, 10, 11, 12], [16, 15, 14, 13]]

Answer 6

><>, length 49, Cracked by Aaron

Regex (Javascript)

^.{7}\n.{12}\n\?.{6};[^v^]{27}(\n.{13}:&.{2}){2}$

Sample output (n=4)

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

Formatting is a bit weird, but checking for number length would have made it a lot longer. Might have gone a bit overboard on the regex, not sure!

Edit: Also I forgot to mention, I use the initial stack (-v flag) for input, not the usual fish input. Sorry!

Original Code:

<v1*2&:
 >:{:}=?v:1+
?^{r0}v;>&:&[r]{&:&2*+}::&:::&*@+@(
+:}=?v>n" "o&:&{1
0~{oa<^v?)*&::&:}

Aaron's is a lot simpler! The complexity of my original code is based around the idea of using n[r] every n-th number to flip that segment (row), then printing all numbers at once at the end

Answer 7

Ohm, cracked

Also my first Cops and Robbers challenge, so tell me if there are issues with this pattern (especially since this is a fairly unknown language).

Regex (PCRE)

^\S{6}\W{0,3}\w$

Output (n = 4)

[[1, 2, 3, 4], [8, 7, 6, 5], [9, 10, 11, 12], [16, 15, 14, 13]]

Answer 8

Ruby [cracked]

First Cops and Robbers challenge. Hope I didn't make this too easy.

EDIT: replaced \g<1> with (?1) because they're evidently equivalent in PCRE.

Regex(PCRE)

^(\W?\W\w){4}..(?1){2}[(-=Z-~]*(?1){5}\w*(?1)(.)\2$

Output (n=4)

[[1, 2, 3, 4], [8, 7, 6, 5], [9, 10, 11, 12], [16, 15, 14, 13]]

(Returns an array of arrays. It's a lambda, BTW, but maybe that gives away too much?)

Answer 9

PHP, 221 Bytes (Cracked)

I hope it is difficult enough.

Regex (PCRE): 16 Bytes

^[^\s/\#6]{221}$

No space, No comments, no use of base64_decode. Have Fun.

Output

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

Original Code

$w=$argv[1];$s="";$r=range(1,$w**2);for($i=0;$i<$w;$i++)if($i%2)array_splice($r,$i*$w,$w,array_reverse(array_slice($r,$i*$w,$w)));foreach(($r)as$v)$s.=str_pad($v,$l=strlen(max($r))+1,"\x20",0);echo(chunk_split($s,$l*$w));

Answer 10

dc, Regex length 12   Cracked by seshoumara!

^[^# !]{59}$

This regular expression is simple enough that I don't think the flavor of regex matters -- it should work across the board. (Note the space after the # in the regex.)

I've tested all four flavors at regex101.com (PCRE/PHP, Javascript, Python, and Golang), as well as the Ruby version at rubular.com. The dc program matches the regex in all five regex versions.

---

The dc program takes its input on stdin and puts its output on stdout.

Sample output for input 4 (there's a trailing space at the end of each line):

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

---

Original code (added after being cracked)

This has been cracked by @seshoumara. Here's my intended code:

?sd[AP]s+0[dddld/2%rld%2*1+ldr-*+1+n2CP1+dld%0=+dvld>l]dslx

Explanation:

?sd      Input number and store it in register d.
[AP]s+   Macro that prints a newline. The macro is stored in register '+'.
0        Push 0 on the stack, initializing a loop.  (The top of the stack is the index variable.  It will go up to d^2-1.)
[        Start a macro definition.  (The macro will be stored in register l.)
ddd      Push 3 copies of the loop index variable on the stack, so they'll be available later. I'll call this number i.
ld/      Divide the last copy of i by d (integer division); this computes the row of the square that we're in (starting with row 0).
2%       Replace the row number with 0 if the row number is even, with 1 if the row number is odd.
r        Swap the top two items on the stack, so the top item is now the next to last copy of i, and the second item on the stack is the row number mod 2.
ld%      Compute i mod d; this goes from 0 to d-1. It is the column in the square that the next number will be placed in.  (The leftmost column is column 0.)
2*1+     Top of the stack is replaced with 2*(column number)+1.
ldr      Inserts d as the second item on the stack.
-        Computes d-2*(column number)-1.
*        The second item on the stack is the row number mod 2, so multiplying yields 0 if the row number is even, and d-2*(column number)-1 if the row number is odd.
+        Add to the remaining copy of i. The sum is i itself in even-numbered rows, and it's i+d-2*(column number)-1 in odd-numbered rows.

The sum at the top of the stack now is the next number we want to print:

• It's easy to see that that's correct if the row number is even, since then the sum is just i.

• For odd-numbered rows, notice that i = d*(i/d)+(i%d) = d * (row number) + column number. It follows that the sum i+d-2*(column number)-1 is d * (row number) + column number + d - 2*(column number)- 1 = d * (row number + 1) - column number - 1, which is the number we want to put in the indicated row and column to ensure that we're counting backwards in the odd-numbered rows.

Returning to the explanation now:

n        Print the desired number for the current row and column.
2CP      Print a space.  (2C, which is computed by dc as 20 + 12, is 32, the ASCII code for a space.)
1+       The original copy of i is at the top of the stack; add 1 to it.
dld%0=+  If (the incremented value of) i is a multiple of d, call the macro at register '+', which prints a newline.
dvld>l   If d > sqrt(i) (in other words, if i < d^2), then go back to the top of the loop by calling macro l again.
]dslx    End the macro definition, store the macro in register l, and execute it.

Answer 11

QBasic, regex length 10 (cracked)

Regex

Should work in any regex flavor, but we'll call it Python flavor.

([A-Z]+.)+

NOTE: My solution uses unformatted QBasic; after formatting, the code doesn't match the regex due to added spaces. (But I can tell you that that's the only change that makes a difference. ([A-Z]+ ?. ?)+ still works on the formatted version.)

For testing purposes, I used QB64 with code formatting turned off (under Options > Code layout). If you don't want to download something, you can also run QBasic online at archive.org (but there you can't turn formatting off).

Sample output

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

Answer 12

C# net46 (Cracked)

(http://ideone.com/ works)

Regex PCRE flavor length 58 tested at regex101

^sta((?![\d%bh\/]|==|if|(\[.*){4}|(i.*){6}).){142}urn....$

Only the method is regexed. Method returns a 2d int[,] array (int[4,4]) for an input n=4. If printed looks like this:

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

This is my first entry into anything like this, let me know if I did anything wrong. Not trying to win by regex length for sure, I'm just interested to see how well I did at preventing cracking :)

Original code:

static int[,]g(int n){int l,j,k=n-n,c,s;var _=new int[n,n];var d=n!=n;c=k;c++;s=k;for(l=k;l<n;l++){for(j=k;j<n;j++){_[l,d?n-j-c:j]=++s;}d=!d;}return _;}

Answer 13

Bash, regex length 38, cracked (@kennytm)

^sort -n <[1adegnopqrstx$\-*()|'; ]+$

Input:

n=4; <command>

Output:

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

Answer 14

Python 3, 55 bytes (Cracked)

PCRE / Python / Golang flavor.

def [triangles=(1,SNAKE)]{27}:print[]SNAKE(--:>or[]{48}

(Be reminded that Full match is required. Assume ^ and $ when testing.)

Sample output:

[1, 2, 3, 4]
[8, 7, 6, 5]
[9, 10, 11, 12]
[16, 15, 14, 13]

---

Original solution:

def r(N,S=1,A=1,K=range,E=list):print(E(K(S,S+N))[::A])or(S+N>N*N)or(r(N,S+N,-A,K,E))

Should have trimmed 4 bytes :p

Answer 15

PHP

I hope this will be a fun one! :D

Output (n=4)

[[1,2,3,4],[8,7,6,5],[9,10,11,12],[16,15,14,13]]

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Level 1: PCRE (length=17) (Cracked by Jörg Hülsermann)

^<[^'"\d{vV;<$]+$

• No single or double quotes so... no strings!
• No digits!
• No { so... no anonymous functions!
• No v so... no eval()!
• No ; so... it must be a single statement!
• No < so... no Heredoc nor multiple PHP blocks!
• The big one! No $ so... good luck defining variables! >:D

---

@JörgHülsermann had an interesting approach, but it's not what I had in mind :). Therefore, I'm introducing a new level of difficulty (I promise I have the code that fits this and I'm not just messing with you):

Level 2: PCRE (length=23) (Cracked by Jörg Hülsermann)

^<[^'"\d{v;<$_~|&A-Z]+$

• All the restrictions of Level 1
• New on this level: none of these _~|&A-Z! :)

---

Have fun!

---

THE ORIGINAL SOLUTION

So, forbidding the $ meant the variables couldn't be accessed the regular way, but that doesn't mean they can't be used at all! You can still use extract()/compact() to import/export variables into the current scope. :)

$i = 1;
// can be written as
extract(['i' => 1])

echo $i;
// can be written as
echo compact('i')['i'];

However, there's a gotcha: compact('x')['x']++ wouldn't work because variables in PHP are passed by value... with one exception! Objects.

$x = (object) ['i' => 1];
// is
extract(['x' => (object) ['i' => 1]]);

// and
compact('x')['x']->i++;
// works just fine!

The rest is easy.

• Numbers 0 and 1 are easily generated by converting false and true to int by prepending them with the + sign
• Use and and or since & and | are forbidden
• To work around the forbidden quotes, just use undefined constants, which are treated as strings
• To suppress the notices generated by using undefined constants, just use @
• The forbidden letter v can be generated by using chr(ord('u') + 1), which translates to @chr(ord(u) + true) using the above workarounds
• The underscore is similar to the above: chr(ord('a') - 2) which translates to chr(ord(a) - true - true)
• Calling functions which contain forbidden characters can be done by taking advantage of PHP's callable type, which can be a string containing the name of the function. So, you can concatenate undefined constants and single character strings generated by ord() to build the name of the function and invoke it like this: array_reverse() becomes (a.rray.chr(ord(a)-true-true).re.chr(ord(u)+true).erse)() (array is a language construct, that's why it's split into the undefined constants a and rray)
• Take advantage of the fact that, when it comes to conditional and loop constructs, the curly brackets are optional if the construct applies just to the immediately following statement. This means you can do stuff like: if ($n = $argv[1] and $i = 0) while ($n > $i++ and do_some and other_stuff or exit)

The logic in human readable code would be:

if (
    $x = (object) [
        'result' => [],
        'i' => 0
    ]

    and

    define('n', $argv[1])

    and

    define('un', '_')

    and

    // create the initial set which we'll loop through
    define('segments', array_chunk(range(1, pow(n, 2)), n))
) while (
    // store each odd segment as-is and increment the "pointer"
    ($x->result[] = @segments[$x->i++])

    and

    // store each even segment reversed and increment the "pointer"
    ($x->result[] = @array_reverse(segments[$x->i++]))

    and

    // check if we need to break out of the loop
    n > $x->i

    or

    // exit and output the result if the above is false
    die(json_encode(
        // if n is odd, the above would have copied a NULL entry 
        // from the segments, so it needs to be filtered out
        array_filter($x->result)
    ))
)

And the unfriendly version that matches the regex:

<?php if (@extract([x=>(object)[s=>[],i=>+false]])and@define(n,compact(arg.chr(ord(u)+true))[arg.chr(ord(u)+true)][+true]?:+true)and@define(un,chr(ord(a)-true-true))and@define(s,(a.rray.un.chunk)(range(+true,pow(n,true+true)),n)))while((@compact(x)[x]->s[]=s[@compact(x)[x]->i++])and(@compact(x)[x]->s[]=(a.rray.un.re.chr(ord(u)+true).erse)(s[@compact(x)[x]->i++]))and(n>@compact(x)[x]->i)or(@die((json.un.encode)((a.rray.un.filter)(@compact(x)[x]->s)))))?>

Answer 16

JavaScript (Cracked)

First time doing a Cops and Robbers challenge, hopefully doing it right.

Regex (JavaScript)

^.*(\.\w+\(.*\)){4}$

Output

An array equal to:

[[1,2,3,4],[8,7,6,5],[9,10,11,12],[16,15,14,13]]

Answer 17

Röda 0.12, length 19 (Cracked by @KritixiLithos)

PCRE:

^{(\|[^\/#\s]*){8}$

Sample output (n=4):

[1, 2, 3, 4][8, 7, 6, 5][9, 10, 11, 12][16, 15, 14, 13]

Original code:

{|n|seq(0,n-1+n%2)|push([{|i|seq(n*i+1,n*i+n)}(_)],[{|j|seq(n*j+n,n*j+1,step=-1)}(_)])|head(n)}

Try it online!

Answer 18

Swift, regex 25 (Cracked)

Right, let's see if I've got the hang of this. This is my first cops and robbers post, so lemme know if I've messed up!

Regex

I used javascript flavour on regex101.com

^.{21}print[^/]{49}o.{7}$

Sample Output

[1, 2, 3, 4]
[8, 7, 6, 5]
[9, 10, 11, 12]
[16, 15, 14, 13]

Original Code

(0..<n).forEach{i in print((0..<n).map{i%2>0 ?(i+1)*n-$0 :i*n+$0+1},separator:",")}

Answer 19

MATL, length 12 (safe)

Regex

Uses Python flavour:

(\w{3}\W){5}

Example output

For n=4:

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

---

Solution

txU:GeG:oEq*S5M*TTx!

To see how this works, consider input n=4.

tx   % Implicit input n, duplicate, delete. So this does nothing
     % STACK: 4
U    % Square
     % STACK: 16
:    % Range
     % STACK: [1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16]
Ge   % Reshape as an n-row array in column major order
     % STACK: [1  5  9 13;
               2  6 10 14;
               3  7 11 15;
               4  8 12 16]
G:   % Push range [1 2 ... n]
     % STACK: [1  5  9 13;
               2  6 10 14;
               3  7 11 15;
               4  8 12 16]
               [1 2 3 4]
o    % Modulo 2
     % STACK: [1  5  9 13;
               2  6 10 14;
               3  7 11 15;
               4  8 12 16]
              [1  0  1  0]
Eq   % Times 2, minus 1 (element-wise)
     % STACK: [1  5  9 13;
               2  6 10 14;
               3  7 11 15;
               4  8 12 16]
              [1 -1  1 -1]
*    % Multiply (element-wise with broadcast)
     % STACK: [1 -5  9 -13;
               2 -6 10 -14
               3 -7 11 -15
               4 -8 12 -16]
S    % Sort each column
     % STACK: [1 -8  9 -16;
               2 -7 10 -15;
               3 -6 11 -14;
               4 -5 12 -13]
5M   % Push [1 -1 1 -1] again
     % STACK: [1 -8  9 -16;
               2 -7 10 -15;
               3 -6 11 -14;
               4 -5 12 -13]
              [1 -1  1  -1]
*    % Multiply (element-wise with broadcast)
     % STACK: [1  8  9  16;
               2  7 10  15;
               3  6 11  14;
               4  5 12  13]
TTx  % Push [true true] and delete it. So this does nothing
!    % Transpose. Implicitly display
     % STACK: [ 1  2  3  4;
                8  7  6  5;
                9 10 11 12;
               16 15 14 13]

Answer 20

C – regex of 42 characters in length – cracked

Javascript regex as used in regex101.

^[-h<=*c+m?{printf("\/a: %d\\',o);}]{137}$

Guessing this will be trivial...

> main 4
1   2   3   4
8   7   6   5
9   10  11  12
16  15  14  13
>

Output is tab-delimited with \n after each line.

My solution, here integers 0 - 2 were obtained via t-t, t/t, and t:

main(int t,char**a){int o=t-t,i=t/t,m,n,h=atoi(*(a+i));for(m=o;m<h;m++)for(n=o;n<h;n++)printf("%d%c",m*h+(m%t?h-n:n+i),n<h-i?'\t':'\n');}

Answer 21

PHP 7 (Safe)

Original Code

for($z=0,$q="";$z<($x=$argv[1])**2;){$w=($d=intdiv($z,$x))%2?($d+1)*$x-$z%$x:($z+1);for($f=0;$f<(log10($x**2)^0)-(log10($w)^0);$f++)$q.="\x20";$q.=++$z%$x?"$w\x20":"$w\n";}print(rtrim($q));

Second Try

Regex (PCRE): 29 Bytes

^[^A-Z#\/\s\>busy_heck]{189}$

No space, No comments, no use of base64_decode.

Many functions are not allowed! underscore

Output n=11

  1   2   3   4   5   6   7   8   9  10  11
 22  21  20  19  18  17  16  15  14  13  12
 23  24  25  26  27  28  29  30  31  32  33
 44  43  42  41  40  39  38  37  36  35  34
 45  46  47  48  49  50  51  52  53  54  55
 66  65  64  63  62  61  60  59  58  57  56
 67  68  69  70  71  72  73  74  75  76  77
 88  87  86  85  84  83  82  81  80  79  78
 89  90  91  92  93  94  95  96  97  98  99
110 109 108 107 106 105 104 103 102 101 100
111 112 113 114 115 116 117 118 119 120 121

Output n=4

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

Output n=3

1 2 3
6 5 4
7 8 9

Answer 22

Jelly, length 14 cracked

cracked by Dennis

[^/P-`mvḊ-ṫ€]*

Python regex.

Added m back in again after I let it slip.

/ (reduce quick);
from P (product) to ` (monad from dyad quick);
m (modulo indexing);
v (eval dyad);
from Ḋ (dequeue) to ṫ (tail); and
€ (for each quick)

For an input of 4 mine outputs:

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

...because I formatted a list of lists as a grid with G.

Answer 23

Jelly, length 17 (safe)

[^/P-`mvÇ-ıḃ-ṫ€]*

Python regex.

Tightening the knot, this bans some more useful things, for your aid here are the banned bytes:

/PQRSTUVWXYZ[\]^_`mvÇÐÑ×ØÞßæçðñ÷øþĊċĖėĠġİıḃḄḅḊḋḌḍḞḟḢḣḤḥḲḳḶḷṀṁṂṃṄṅṆṇṖṗṘṙṚṛṠṡṢṣṪṫ€

just under a third of them!

For an input of 4 mine outputs:

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

...because I formatted a list of lists as a grid with G.

A solution:

’:2o1
Ḃ¬aẋ@0
’r0;0ẋ$ẋ1Ŀ¬0¦;2ĿÆ¡œ?⁸²¤s⁸G

Try it online! / regex101

The main trick here is to index into a lexicographically sorted list of the permutations of the natural numbers up to n² (using œ? to avoid building the list of length n²!), and to split the result into chunks of length n. The aforementioned index is found by forming its representation in the factorial number system which is formulaic since the "unsliced" snake is created by permuting elements in a prescribed manner (this may be readily converted to a number with Æ¡).

The solution I present uses Ŀ to reference previous links as monads (replacing Ñ and Ç), but multiple $ in a row could be employed instead to "inline" these helper functions. It also uses r since Ḷ and R are banned.

’:2o1 - Link 1, periodic repetitions in the factorial base representation: n
’     - decrement n
 :2   - integer divide by 2
   o1 - or 1 (keep one period in the cases n=1 and n=2)

Ḃ¬aẋ@0 - Link 2, n zeros if n is even, else an empty list: n
Ḃ      - mod 2
 ¬     - not
   ẋ@0 - 0 repeated n times
  a    - and

’r0;0ẋ$ẋ1Ŀ¬0¦;2ĿÆ¡œ?⁸²¤s⁸G - Main link: n                    e.g. 6
’r0                        - inclusive range(n-1, 0)              [5,4,3,2,1,0]
    0ẋ$                    - 0 repeated n times                   [0,0,0,0,0,0]
   ;                       - concatenate (makes one "period")     [5,4,3,2,1,0,0,0,0,0,0,0]
        1Ŀ                 - call link 1 as a monad               2
       ẋ                   - repeat list                          [5,4,3,2,1,0,0,0,0,0,0,0,5,4,3,2,1,0,0,0,0,0,0,0]
           0¦              - apply to index 0 (rightmost index):
          ¬                -     not (make the last 0 a 1)        [5,4,3,2,1,0,0,0,0,0,0,0,5,4,3,2,1,0,0,0,0,0,0,1]
              2Ŀ           - call link 2 as a monad               [0,0,0,0,0,0]
             ;             - concatenate                          [5,4,3,2,1,0,0,0,0,0,0,0,5,4,3,2,1,0,0,0,0,0,0,1,0,0,0,0,0,0]
                Æ¡         - convert from factorial base          45461852049628918679695458739920
                      ¤    - nilad followed by link(s) as a nilad
                    ⁸      -     left argument, n                 6
                     ²     -     square                           36
                  œ?       - lexicographical permutation lookup   [1,2,3,4,5,6,12,11,10,9,8,7,13,14,15,16,17,18,24,23,22,21,20,19,25,26,27,28,29,30,36,35,34,33,32,31]
                       s⁸  - split into chunks of length n        [[1,2,3,4,5,6],[12,11,10,9,8,7],[13,14,15,16,17,18],[24,23,22,21,20,19],[25,26,27,28,29,30],[36,35,34,33,32,31]]
                         G - format as a grid

Answer 24

Powershell, 23 Bytes

Cracked By Matt

^.+?%.{42}%.{11}:.{35}$

Original Solution:

$n="$args";$script:r=0;$a=1..$n|%{$t=++$script:r..($script:r+=$n-1);if(!($_%2)){[Array]::Reverse($t)};,$t};$a|%{$_-join" "}

Takes input as argument and outputs to stdout

Hopefully this regex is OK, I don't expect this being too difficult to crack, as I haven't obfuscated much of it, and the regex gives a good few starting points to fill in the gaps, there's one thing in the first segment which is very uncommon in code golf though, which may catch someone out, I think a non-greedy match is required there to make this a bit tougher.

First cops challenge anyway.

1..4 | % { "----$_----" ; .\snake-cops.ps1 $_  }
----1----
1
----2----
1 2
4 3
----3----
1 2 3
6 5 4
7 8 9
----4----
1 2 3 4
8 7 6 5
9 10 11 12
16 15 14 13

Answer 25

Pip, regex length 3 (safe)

The solution is a full program that takes n as a command-line argument. It does not use any command-line flags.

Regex (any flavor)

\w+

Sample output

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

---

My solution

YENsXaPBsPOyY_MUyFi_MUENsXaIiBA1PsPUPODQENsXiXaPBsX_PBsMRVyEI1PsPUPODQENsXiXaPBsX_PBsMy

Try it online!

Strategy

Here's the code we would like to write:

Y \,a
F i ,a
 I i%2
  P i*a+_.s M RVy
 E
  P i*a+_.s M y

That is:

• Store the numbers 1 through a in y
• Loop over values of i from 0 through a-1
• If i is odd, reverse y, add i*a to each element, concatenate a space to each element, and print
• Otherwise, do the same thing, but without reversing first

Difficulties

A lot of commands and variables in Pip use letters, but some important ones don't:

• Range and inclusive range (, and \,)
• Most math operations (+, -, *, %, ++)
• Assignment (:)
• We can't have a loop or function body with more than one statement (that would need {})
• We can't use parentheses to enforce precedence

How we get around those limitations:

• ENumerate can be used in place of ,; we just need a string with the number of characters we want, and we need to extract the first element of each sublist in a structure like [[0 "H"] [1 "i"]].
• We don't need to increment anything if we can solve the problem with For loops.
• We can assign to the y variable with the Yank operator.
• We can do math with strings: X is string multiplication, and PUsh (or PB "push-back") will concatenate a string to another string in-place. To take the length of a string, we can ENumerate it and extract the right number from the resulting list.
• We can use functions as long as they can be written as single-expression lambda functions using _.

Specifics

The building blocks of our program:

Range

_MUENsXa

That's map-unpack(_, enumerate(repeat(space, a))) in pseudocode. Map-unpack is like Python's itertools.starmap: given a list of lists, it calls a function on the items of each sublist. _ returns its first argument, so _MU just gets the first item of each sublist. For example, if a = 3:

     sXa  "   "
   EN     [[0 " "] [1 " "] [2 " "]]
_MU       [0 1 2]

... which is the same as ,a.

Inclusive range

I'm not sure there's a way to do inclusive-range(1, a) in a single expression, but fortunately we only need it once, so we can construct it in the y variable in three steps.

YENsXaPBs

In pseudocode, yank(enumerate(repeat(space, a).push-back(space))):

   sXa     "   "
      PBs  "    "
 EN        [[0 " "] [1 " "] [2 " "] [3 " "]]
Y          Store that in y

Next POy pops the first item from y and discards it, leaving [[1 " "] [2 " "] [3 " "]].

Finally,

Y_MUy

That is, yank(map-unpack(_, y)): extract the first element of each sublist and yank the resulting list back into y. y is now [1 2 3].

Length

PODQENaPBs

In pseudocode, pop(dequeue(enumerate(a.push-back(space)))). The difficulty here is that enumerate only gives us numbers up to len(a)-1, but we want len(a). So we first push a space to a, lengthening it by one character, and then take len-1 of the new string.

      a     "xyz"
       PBs  "xyz "
    EN      [[0 "x"] [1 "y"] [2 "z"] [3 " "]]
  DQ        [3 " "]
PO          3

Math

Now that we have a way to take the length of strings, we can use strings to do multiplication and addition of numbers:

PODQENsXaXbPBs
PODQENsXaPBsXbPBs

The first does sXaXb to create a string of a*b spaces and then takes the length of it; the second does sXaPBsXb to push a string of b spaces to a string of a spaces and then takes the length of it.

The nice part is that all the operators we're using here (PU, PO, PB, DQ, EN, X) can be used with _ to form lambda expressions. So we can map mathematical transformations to the inclusive range we constructed earlier.

We also need to check i%2 inside the loop, but this is easily accomplished with bitwise AND: iBA1.

Put them together

The full code, with some added whitespace:

YENsXaPBs POy Y_MUy              Get \,a into y
F i _MUENsXa                     For i in ,a
 I iBA1                           If i%2=1
  P sPUPODQENsXiXaPBsX_PBs M RVy   Print sPUi*a+_ M RVy
 EI1                              Elseif 1 (using E would cause a parsing problem)
  P sPUPODQENsXiXaPBsX_PBs M y     Print sPUi*a+_ M y

Answer 26

Mathematica, regex length 11, non-competing, cracked

PCRE flavour:

^[^]@]{49}$

The correct solution will be a function which takes an integer and returns the output as a nested list like:

{{1, 2, 3, 4}, {8, 7, 6, 5}, {9, 10, 11, 12}, {16, 15, 14, 13}}

Answer 27

CJam, PCRE, length 8, cracked

^[a-~]*$

Example output for 4:

[[1 2 3 4] [8 7 6 5] [9 10 11 12] [16 15 14 13]]

Answer 28

tinylisp, regex length 3 (cracked)

You can test tinylisp code at Try it online!

Regex (any flavor)

\S+

Time to go hardcore.

Output

The solution defines a function that takes a single integer argument and returns a list like this (for n=4):

((1 2 3 4) (8 7 6 5) (9 10 11 12) (16 15 14 13))

---

My original code uses the same basic idea Brian McCutchon came up with, building lists and eval'ing them. Here it is in one line:

(v(c(h(q(d)))(c(h(q(d')))(c(c(h(q(q)))(c(c()(c(q(arglist))(c(c(h(q(v)))(c(c(h(q(c)))(c(c(h(q(q)))(q(d)))(q(arglist))))()))())))()))()))))(d'(seq-args(c(h(q(start)))(c(h(q(stop)))(c(h(q(step)))())))))(d'(seq(c(c(h(q(accum)))seq-args)(q((i(e(v(h(q(start))))stop)(c(v(h(q(start))))accum)(seq(c(v(h(q(stop))))accum)start(s(v(h(q(stop))))step)step)))))))(d'(f'(c(c(h(q(index)))(c(h(q(size)))seq-args))(q((i(e(v(h(q(index))))size)()(c(seq()start(v(h(q(stop))))step)(f'(a(h(q(1)))index)size(a(v(h(q(stop))))size)(a(v(h(q(start))))size)(s(h(q(0)))step)))))))))(d'(f(q((size)(f'(h(q(0)))size(h(q(1)))size(h(q(1))))))))

I used the full construct-and-eval method once, to define a macro d' that makes definitions like d, but takes its arguments wrapped in a list: so instead of (d x 42), you can do (d'(x 42)). Then it was just a matter of rewriting any lists in the definitions that might need whitespace: (q(a b)) -> (c a(q(b))) -> (c(h(q(a)))(q(b))).

Answer 29

CJam, PCRE, length 9, cracked

^[a-z~]*$

Example output for 4:

[[1 2 3 4] [8 7 6 5] [9 10 11 12] [16 15 14 13]]

Now {|} are banned, too.

Answer 30

Python3, (PCRE) length 27 (Cracked!)

Regex: ^([^# 0]){115}.{6}(?1){24}$

My first Cops and Robbers submission.

Output format

4:
[1, 2, 3, 4]
[8, 7, 6, 5]
[9, 10, 11, 12]
[16, 15, 14, 13]

Original code: n=int(input());j=0;exec("print([int(i%n+1+(2*n-(2*(i%n)+1))*((((i/n)//1+1)/2)//1)+(2*(i%n)+1)*int(int(i/n)/2))for i in range(j,j+n)]);j+=n;"*n)

Answer 31

Python3, length 162 (Cracked!)

Regex: ^([^"' #]){24}"(?1){11}i%n(?1){4}2\*n-(?1){4}i%n(?1){10}i\/n(\)\/\/1)(?1){5}(?2)(?1){3}2\*\(i%n\)(?1){4}[int()2\/]{16}for i in range\(j,(?1){4}\]\)(?1){6}\"\*n\)$

Okay, I know, it's quite long. Fortunately, it won't be cracked in under a week... :'D.

I think I didn't make a mistake anywhere, that would allow loophole-y answers.

Output format

4:
[1, 2, 3, 4]
[8, 7, 6, 5]
[9, 10, 11, 12]
[16, 15, 14, 13]

Original code:n=int(input());j=0;exec("print([int(i%n+1+(2*n-(2*(i%n)+1))*((((i/n)//1+1)/2)//1)+(2*(i%n)+1)*int(int(i/n)/2))for i in range(j,j+n)]);j+=n;"*n)

Answer 32

Actually, Python regex of length 193 (safe)

^[^\x00-\x08\x0d-\x13\x16-\x1d\x3f\xa6\xb6\xc1\xe9\xea\xfa\xff]{5}[\x00-\x08\x0d-\x13\x16-\x1d\x3f\xa6\xb6\xc1\xe9\xea\xfa\xff][^\x00-\x08\x0d-\x13\x16-\x1d\x3f\xa6\xb6\xc1\xe9\xea\xfa\xff]{6}$

This regex matches the CP437-encoded program source.

Output for n = 4:

[[1, 2, 3, 4], [8, 7, 6, 5], [9, 10, 11, 12], [16, 15, 14, 13]]

Here is a Python 3 program to help with testing:

import re
pattern = re.compile(rb'[^\x00-\x08\x0d-\x13\x16-\x1d\x3f\xa6\xb6\xc1\xe9\xea\xfa\xff]{5}[\x00-\x08\x0d-\x13\x16-\x1d\x3f\xa6\xb6\xc1\xe9\xea\xfa\xff][^\x00-\x08\x0d-\x13\x16-\x1d\x3f\xa6\xb6\xc1\xe9\xea\xfa\xff]{6}')
code = b'code here'
print(pattern.match(code) and True or False)

Try it online!

---

Actually, 12 bytes

;²R╡"?R"ß*♀ƒ

Try it online!

Explanation:

;²R╡"?R"ß*♀ƒ
;             duplicate input
 ²R           range(1, n**2+1)
   ╡          split into n-length chunks
    "?R"ß*    "?R"*n
          ♀ƒ  for each chunk: reverse if index is odd (R) else do nothing (?)

Answer 33

Scala, length 40, Cracked

Regex (PCRE)

[\w\s]+[\w\(\):]+[\w\(\)<\-\s{=;+*%\.}]+

Output (n=4)

Vector(Vector(1, 2, 3, 4), Vector(8, 7, 6, 5), Vector(9, 10, 11, 12), Vector(13, 14, 15, 16))

Code

def x(y:Int)=for(u<-1 to y)yield{val q=for(z<-1 to y;r<- List(z+(y*(u-1))))yield r;if(u%2==1)q else q.reverse}

Ungolfed

def x(y:Int)=
  for(u<-1 to y)
      yield {
          val q=for(z<-1 to y;r<- List(z+(y*(u-1)))) yield r;
          if(u%2==1)
            q 
          else 
            q.reverse
      }

Answer 34

05AB1E, length 22 Cracked by Emigna

This is probably too easy.

Regex (PCRE)

^([E-Z0]*[ˆ>*}<]){7}$

Output

[[1, 2, 3, 4], [8, 7, 6, 5], [9, 10, 11, 12], [16, 15, 14, 13]]

Original Solution

UXL0KVXLˆXGXN>*LYKZL0KVNFR}<>ˆ

Answer 35

Jelly, length 12 - cracked

cracked by Dennis

^[^ḊḢṚUṖṪ]*$

Python regex (although I think all flavours are valid for this pattern).

That's right, none of those lovely array manipulation atoms!
No:

• Ḋequeue;
• Ḣead;
• Ṛeversal;
• Upend;
• Ṗop; or
• Ṫail;

For an input of 4 mine outputs:

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

...because I formatted a list of lists as a grid with G.

Answer 36

Jelly, length 13 cracked

cracked by ais523

[^ḊḢṚUmṖṪVv]*

Python regex (although I think all flavours are valid for this pattern).

An extension of my previously cracked entry:
I have banned modulo indexing, which I missed and Dennis cleverly used;
I have banned use of the two eval atoms, as they'd allow indirect usage of the banned atoms; and
I have removed the start and end match (^...$ since it is redundant since a full match is required).

No:

• Ḋ dequeue;
• Ḣ head;
• Ṛ reversal;
• U upend;
• m modulo indexing;
• Ṗ pop;
• Ṫ tail;
• V eval; or
• v dyadic eval

For an input of 4 mine outputs:

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

...because I formatted a list of lists as a grid with G.

Answer 37

Jelly, length 13 cracked

cracked by Dennis (I forgot to keep m ... another incoming)

[^/P-`vḊ-ṫ€]*

Python regex (although I think all flavours are valid for this pattern).

Severely increased the banned characters from my previous submission:

/ (reduce quick);
from P (product) to ` (monad from dyad quick);
v (eval dyad);
from Ḋ (dequeue) to ṫ (tail); and
€ (for each quick)

For an input of 4 mine outputs:

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

...because I formatted a list of lists as a grid with G.

Answer 38

Jelly, 15 bytes, Cracked

Jelly seems to be quite popular in this challenge. So let's require the use of a totally different algorithm. The regex, PCRE interpreted in Jelly's encoding:

[^œŒ]{12}
Çœ?²s

Several PCRE matchers, such as pcregrep and even perl itself, will treat input by default as "unknown 8-bit character set compatible with ASCII"; therefore, they handle Jelly's encoding just fine. (That said, I suspect you need to use perl here as many regex matchers dislike newlines in the middle of the regex. I can't just write it as \n as that's a byte longer.)

Result for an input of 4:

[[1, 2, 3, 4], [8, 7, 6, 5], [9, 10, 11, 12], [16, 15, 14, 13]]

Crack

This ended up being cracked due to a typo in the regex. I'll submit a fixed version.

Answer 39

tinylisp, regex length 10 (cracked)

You can test tinylisp code at Try it online!

Regex

Any flavor should work the same, we'll call it Python flavor.

[( )1c-s]+

Basically this boils down to, "Solve the problem without using the library." If that turns out to be too easy, I may post a more restrictive one.

Output

The solution is a function that takes a single integer argument and returns a list like this (for n=4):

((1 2 3 4) (8 7 6 5) (9 10 11 12) (16 15 14 13))

Answer 40

PHP (Cracked)

Output (n=4)

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

---

PCRE (length=31)

^.{4}[-"$%&*+:;=?{}a-zMZ]+.{4}$

Here's another take on this challenge, this time using a whitelist approach.

The notable forbidden characters are (), [], _, digits and most of the upper case letters.

Looking forward to see what you come up with!

---

THE ORIGINAL SOLUTION

This one was simpler. Since parenthesis were forbidden, you couldn't use function calls or language constructs like conditionals and loops which meant the infamous goto was the solution! >:D

• The only number my solution requires is 1, which I defined as +true.
• To format the output I used tab and newline characters, generated using bitwise operators on strings: "M" & "+" and "Z" & "*" Start by outputting 1
• Then, I looped through each number and calculated the difference between each column and it's complement, which I multiplied by 0 for odd rows and 1 for even rows and then added to the original number at that position.

So, for n=4, 5 would originally be on the first column (1) on an odd row.

The difference is -2 * $column + $n + 1 = 3, which means 5 becomes 5 + $difference * $multiplier = 5 + 3 * 1 = 8. So, the first column of row number 2 becomes 8;

A human readable version of my solution is

<?=

$one = $i = 1;
$multiplier = $one - $one;
$n = $argv{$one};

loop:

++$i == $n * $n + $one && die;

$column = $i % $n ?: $n;
$difference = -$column - $column + $n + $one;

print "M"&"+";

$i % $n == $one && print "Z"&"*";

print $i + $difference * $multiplier;

// if not at the end of the row, leave as is
// else convert 0 to 1 and 1 to 0 to apply (or not) the above difference
$multiplier = $i % $n ? $multiplier : -$multiplier + $one;

goto loop

?>

My solution that matches the regex was: <?= $t=$i=+true;$f=$s=$t-$t;$n=$argv{$t};a:++$i==$n*$n+$t&&die;$b=$i%$n?:$n;$m=-$b-$b+$n+$t;print"M"&"+";$i%$n==$t&&print"Z"&"*";print$i+$m*$s;$s=$i%$n?$s:-$t*$s+$t;goto a?>

Answer 41

Go, length 17 cracked

Regex, PCRE:

^[^+-<]+.[^+-<]+$

Translated roughly, you can use neither of these characters, except once:

+ , - . / 0 1 2 3 4 5 6 7 8 9 : ; <

The regex matches the full program from package main to func main() which reads from stdin like so: echo 4 | go run snake.go

Output:

[[1 2 3 4] [8 7 6 5] [9 10 11 12] [16 15 14 13]]

Answer 42

QBasic, regex length 10 (cracked)

A (hopefully more challenging) variation on my first submission.

Regex

Same as before. Should work in any regex flavor, but we'll call it Python flavor.

([A-Z]+.)+

My solution uses unformatted QBasic; after formatting, the code doesn't match the regex due to added spaces. (But ([A-Z]+ ?. ?)+ still works on the formatted version.)

This time, I'm requiring that a crack work at archive.org, which allows a bit less flexibility in syntax than QB64 does. ;)

Sample output

|1 |2 |3 |4 |
|8 |7 |6 |5 |
|9 |10|11|12|
|16|15|14|13|

(I've used the ASCII pipe character | here, but the similar-looking box-drawing character │--code point 179 in the code page that QBasic uses--works just as well and makes the chart look a lot nicer. You can insert it in your code by holding down Alt and typing 179 on the numpad. </funfacts>)

---

My original solution, prettified (to get the regex to match, replace \n * with :):

CLS

DIM SEP AS STRING
READ SEP
INPUT SIZE
NEGONE=NOT ZERO
ONE=ZERO-NEGONE
THREE=ONE+ONE+ONE
TEN=THREE*THREE+ONE

CLS
FIELDWIDTH=ONE
TMP=SIZE*SIZE
DO
  FIELDWIDTH=FIELDWIDTH+ONE
  TMP=TMP\TEN
LOOP WHILE TMP

FROMVAL=ONE
TOVAL=SIZE
DIRECTION=ONE

FOR ROW=ONE TO SIZE
  COL=ONE
  FOR VALUE=FROMVAL TO TOVAL STEP DIRECTION
    LOCATE ROW,COL
    PRINT VALUE
    LOCATE ROW,COL
    PRINT SEP
    COL=COL+FIELDWIDTH
  NEXT
  LOCATE ROW,COL
  PRINT SEP
  TMP=FROMVAL+SIZE
  FROMVAL=TOVAL+SIZE
  TOVAL=TMP
  DIRECTION=ZERO-DIRECTION
NEXT

DATA|

Answer 43

Racket Intermediate Student with Lambda, regex length 36 20 22, Cracked by kennytm

Produces a function that takes n as input and returns the answer as a list of lists.

Regex (JS)

^((?![nla][peo]|-).)*$

Output

(list (list 1 2 3 4) (list 8 7 6 5) (list 9 10 11 12) (list 16 15 14 13))

Answer 44

Racket Intermediate Student with Lambda, regex length 27 22 10 (Cracked)

You can run Racket ISL with Lambda at Try it online!.

Produces a function that takes n as input and returns the answer as a list of lists. The basic idea is that only one-character words are allowed, possibly prefixed with con. Also, besides the con exception, every other character must be non-word. Now let's see if any con robber can crack it!

Regex (JS)

(con|.\W)+

Output

(list (list 1 2 3 4) (list 8 7 6 5) (list 9 10 11 12) (list 16 15 14 13))

Edit 3/14

I've golfed the regex down quite a bit, making it more restrictive in the process. The basic idea of the solution is the same, but since the regex is not equivalent to the previous, I'll count my 7 days starting now. Also, until told otherwise, I'll assume that the answer's requirement for a full match means that ^ and $ on the regex are implied.

Original solution

(λ (n) (((((λ(f) ((λ (x) (x x)) (λ (x) (f (λ (y)((x x)y)))))) (λ (q) (λ(n) (λ(c) (λ(r) (cond [(< c 0)r][(= 1 1) (((q n) (- c 1))(cons(cond [(= 0((((λ (f) ((λ (x) (x x)) (λ (x) (f (λ (y)((x x)y)))))) (λ (r) (λ(a)(λ (b) (cond [(< a b)a][(= 1 1)((r(- a b)) b)])))))c)2))((((((λ (f) ((λ (x) (x x)) (λ (x) (f (λ (y)((x x)y)))))) (λ (r)(λ (s) (λ(e) (λ(t) (λ(a) (cond [(>= (* t s) (* t e)) a][(= 1 1)((((r s) (- e t)) t) (cons(- e t)a))])))))))(+ 1(* c n))) (+ 1(* c n)n)) 1) '())][(= 1 1) ((((((λ (f) ((λ (x) (x x)) (λ (x) (f (λ (y)((x x)y)))))) (λ (r) (λ(s) (λ(e) (λ(t) (λ(a) (cond [(>= (* t s) (* t e)) a][(= 1 1)((((r s) (- e t)) t) (cons(- e t)a))]))))))) (+ (* c n)n))(* c n))-1) '())]) r))]))))))n) (- n 1)) '()) )

Try it online! (Note that the TIO code is slightly different because I've wrapped the solution in (... 4) to call it.)

I picked ISL with Lambda over standard Racket on this and my other answer because I wanted to have short regexes and minimize loopholes. To do it, I started with this:

(define Y
  (λ (f)
     ((λ (x) (x x))
      (λ (x) (f (λ (y) ((x x) y)))))))

(define % (Y (λ (r) (λ (a) (λ (b)
  (cond [(< a b) a]
        [(= 1 1) ((r (- a b)) b)]))))))

(define range1 (Y (λ (r) (λ (s) (λ (e) (λ (t) (λ (a)
  (cond [(>= (* t s) (* t e)) a]
        [(= 1 1) ((((r s) (- e t)) t) (cons (- e t) a))]))))))))

(define g (Y (λ (q) (λ (n) (λ (c) (λ (r)
  (cond
    [(< c 0) r]
    [(= 1 1)
     (((q n) (- c 1))
      (cons
        (cond [(= 0 ((% c) 2))
               ((((range1 (+ 1 (* c n))) (+ 1 (* c n) n)) 1) '())]
              [(= 1 1) ((((range1 (+ (* c n) n)) (* c n)) -1) '())])
        r))])))))))

(define (f n)
  (((g n) (- n 1)) '()))

(Look familiar? I translated this into tinylisp for a certain crack.) Y it the applicative-order Y combinator, taken from this blog post. All functions are curried to make using the Y combinator possible. Then I substituted the function bodies in for each reference to a function and turned f into a lambda. After that, all I had to do was play with spaces so that I could use .\W instead of .\W+ in my regex.

Answer 45

Java 8 (Safe)

Regex (PCRE): 6 Bytes

[^yD]*

Output n=4

Output separated by spaces

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

Solution

The difficulty is getting to System.out without using the letter y. FileDescriptor is also forbidden because of D. Thus, reflection is heavily used to derive System.

class Snake {
  public static void main(String[] args) throws Exception {
    int n = Integer.parseInt(args[0]);
    String[][] ret = new String[n][n];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < n; j++) {
        int d = (i % 2 == 0) ? j + 1: n - j;
        ret[i][j] = "" + (i * n + d);
      }
    }
    String stem = "S" + (char)(1 + (int)'x') + "stem";
    String loaderMethod = "get" + stem + "ClassLoader";
    ClassLoader cl = (ClassLoader)ClassLoader.class.getMethod(loaderMethod).invoke(null);
    Class sClass = cl.loadClass("java.lang." + stem);
    for (int i = 0; i < n; i++) {
      String s = String.join(" ", ret[i]);
      ((java.io.PrintStream)sClass.getField("out").get(null)).println(s);
    }
  }
}

Answer 46

Jelly, 16 bytes, Cracked

This is my previous submission with a typo/thinko in the regex fixed.

Jelly seems to be quite popular in this challenge. So let's require the use of a totally different algorithm. The regex, PCRE interpreted in Jelly's encoding:

[^œŒ]{12}
Çœ\?²s

Several PCRE matchers, such as pcregrep and even perl itself, will treat input by default as "unknown 8-bit character set compatible with ASCII"; therefore, they handle Jelly's encoding just fine. (That said, I suspect you need to use perl here as many regex matchers dislike newlines in the middle of the regex. I can't just write it as \n as that's a byte longer.)

Result for an input of 4:

[[1, 2, 3, 4], [8, 7, 6, 5], [9, 10, 11, 12], [16, 15, 14, 13]]

Crack

The crack again rather misses the point of the question, but I'll have to give up on this unless I can find a way to avoid cheating. (The newline and Ç was part of that, but @Dennis simply output via stdout rather than via the return value to avoid the issue. Is it acceptable to force a certain sort of I/O in cops-and-robbers challenges?)

Answer 47

PHP (Cracked)

start from the command line

php -r <code> <args>

original code

$a=array();foreach($r=range(0,($z=$argv{1})-1)as$g)foreach(($r)as$f)$a{$g}{$f}=$g%2?$g*$z+$z-$f:$g*$z+$f+1;echo(serialize($a));

Regex (PCRE): 18 Bytes

^[$-2:-?a-}]{127}$

Output n=4

a:4:{i:0;a:4:{i:0;i:1;i:1;i:2;i:2;i:3;i:3;i:4;}i:1;a:4:{i:0;i:8;i:1;i:7;i:2;i:6;i:3;i:5;}i:2;a:4:{i:0;i:9;i:1;i:10;i:2;i:11;i:3;i:12;}i:3;a:4:{i:0;i:16;i:1;i:15;i:2;i:14;i:3;i:13;}}

Answer 48

><>, length 27 + 1 for single-line mode = 28

Regex (PCRE), using single-line mode :

^(?=(.*\n){3})[^.,\d]{131}$

My program takes the input from the stack with -v, uses no jumps, no digits, no commas and exactly three linefeeds and 131 chars.

Output for n=4 :

1,2,3,4
8,7,6,5
9,10,11,12
16,15,14,13

Answer 49

Ruby (2nd submission)

The outside is mostly the same but my accidenal loophole is more restrictive now. I have many regrets

(\W?\W\w){4}..(?1){2}\W{8}(\w.\w)...\2(?1){5}\w*(?1)(.)\3

It's a lambda. Output is an array of arrays. Example with (n=4):

[[1, 2, 3, 4], [8, 7, 6, 5], [9, 10, 11, 12], [16, 15, 14, 13]]

Answer 50

PHP >=5.4 (Safe)

Original Solution

<?while(+$g<$a=$argv{1})echo(join("\t",$g%2?range($g*$a+$a,$g++*$a+1):range($g*$a+1,$g++*$a+$a))),"\n"?>

start from the command line

php <file> <args>

Regex (PCRE): 12 Bytes

[^ ;#/]{104}

Output n=4

separator is \t

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

Answer 51

PHP >=7.0 (Safe)

Original Solution

<?php while($g<$a=$_GET{0})echo($g%2?"\u{202e}":""),join("\t",array_map($g%2?strrev:trim,range($g*$a+1,$g++*$a+$a))),"\n"?>

Regex (PCRE): 30 Bytes

<\?php [^; >]{32}\\u[^; >]{82}>

Sorry a little mistake the week counts from now

Hint: Use a special unicode Character

Output n=4

separator is \t. Looks like this

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

Output n=4

only copy and paste from the output I use $_GET and the document sents this header Content-Type: text/plain;charset=utf-8

1   2   3   4
‮5  6   7   8
9   10  11  12
‮31 41  51  61