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

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 2

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 3

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 4

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 5

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 6

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 7

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 8

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 9

PHP (Cracked)

Output (n=4)

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

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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!

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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 10

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 11

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!

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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 12

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 13

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>)

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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 14

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 15

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 16

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 17

><>, 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 18

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 19

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 20

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 21

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