A Different Kind of Meta Regex Golf

Notice: Following popular demand I have slightly relaxed the rules:

• The maximum regex size grows by 1 byte every 5 answers. Answer N may use up to 29 + ⌈N/5⌉ bytes.
• The score of each answer will be (M/(30+N/5))N

In regex golf, you're given two sets of strings, and are asked to create the shortest regex which matches all strings in the first set, but fails on all strings in the second set.

That is what we're going to do, but each time someone answers, their regex itself will be added to one of the two sets of strings (of their own choice). Therefore, there is a strict order to answers in this challenge.

Let's go through an example:

• Say I start this with abc (which I won't), and put it in the match set.
• Then a valid second answer would be a, as it matches the above (and there are no strings that need to fail yet). Say this answer goes in the fail set.
• Now the third answer has to match abc but fail on a. A possible third answer is therefore b. Let's put this in the match set.
• The fourth answer now has to match abc and b, but fail on a. We'll disallow duplicate answers, so a valid regex would be c|b.

What's important is that your answer should be as short as possible. This may be trivial for the first few answers, but once we get a few answers, it should get harder and harder to get the desired match in as few characters as possible.

For the actual challenge, initially the match set contains PPCG and the fail set contains [PPCG], and I have already provided the first answer.

There should never be two answers with the same N. If two people happen to simultaneously answer for some N, the one who answered later (even if it's a few seconds difference) should graciously delete their answer.

To make this run a bit smoother, try to stick to the following steps when posting your answer:

• Make sure that someone has independently verified the correctness of the previous answer (and left a corresponding comment).
• Take the two test sets found in the previous answer, and write a regex which matches all strings in one set and none in the other.

# N. [regex flavour] - [regex size in bytes]

[regex]

[notes, explanation, observations, whatever]

### The next answer has to match the following strings:

[match set]

### And fail on these strings:

[fail set]


where N is the number of your answer. Please copy [match set] and [fail set] from the previous answer, and append your regex to one of them.

This is absolutely vital to the challenge! I've provided a dashboard tool for the challenge to help with the bookkeeping, and it relies on the above template. (See bottom of the post.)

These regulations may seem rather strict, but they are necessary to avoid invalid answers somewhere up the chain.

Rules

• A user may only submit one answer per 4 hour period. (This is to prevent users from constantly watching the question and answering as much as possible.)
• A user may not submit two answers in a row. (e.g. since I submitted answer 1 I can't do answer 2, but I could do 3.)
• Do not edit answers that have been verified. (Even if you find a way to shorten it!)
• Should a mistake be discovered earlier in the chain (i.e. after follow-up answers have been posted), the offending answer should be deleted and will be removed from the set of strings that new submissions should fail on. However, all answers that have been posted since should not be changed to reflect.
• Clearly state one flavour your regex is valid in. You may choose any flavour that is freely testable online. There's a good list of online testers over on StackOverflow. In particular, Regex101 and RegexPlanet should be useful, as they support a wide variety of flavours. Please include a link to the tester you chose in your answer. By switching on the global and multiline modifiers in the tester, you can test all strings at once, one on each line (these modifiers are not counted towards your regex size, because they aren't needed on any individual string).
• Your regex must not be empty.
• Your regex for answer N must not be longer than 29 + ⌈N/5⌉ bytes. I.e. answers 1 to 5 may use up to 30 bytes (inclusive), answers 6 to 10 may use up to 31 bytes... answers 31 to 35 may use up to 36 bytes. Check the dashboard to see how many characters the next answer may use.
• Your regex must not be identical to any string in either test set.
• Do not include delimiters in your submission or byte count, even if the relevant host language uses them. If your regex uses modifiers, add one byte per modifier to the regex size. E.g. /foo/i would be 4 bytes.

Scoring

Each answer's score is calculated as (M/(30+N/5))N, where M is the size of the regex in bytes, and N is it's number. Each user's score is the product of all their answers. The user with the lowest overall score wins. In the unlikely event of a tie, the user with the latest submission wins. I will accept that user's latest answer.

If you prefer summing scores, you can calculate each answer's score as N * (log(M) - log(30)) and sum those up over all answers. That will give the same leaderboard order.

There is no need to include an answer's score in the answer, just report M. The challenge dashboard at the bottom of the question will compute the scores, and in the event of two very close scores, I'll double check the results using arbitrary-precision types.

Note that the score of each answer is less than 1, so you can improve your overall score by providing a new answer. However, the shorter each of your submissions, the more efficiently you can lower your score. Furthermore, later answers can achieve a lower score although being longer, due to the increasing exponent.

Dashboard

I've written a little Dashboard tool, using Stack Snippets, based on Optimizer's work over here. I hope this will help us get some order into these answer-dependent challenges.

This will display the current status of the challenge - in particular, if there are conflicting answers, if an answer needs to be verified, or if the next answer can be posted.

It also produces a list of all answers with scores, as well as a leaderboard of all users. Please stick to the challenge format above, so the dashboard can read out the relevant strings from your answers. Otherwise you might not be included in the leaderboard.

Please let me know (ideally in chat) if you spot any bugs or have some ideas how the usefulness of the tool could be improved.

...\^.P|^!|G]$|w|<!|^\^?P ([^\\}<]{3}|][^]]|^).?[PG] ^(..[^^].{4,22}$|[^?]+\w)$|2 ^(..[^^].{4,22}$|[^?]+\w)|~ ^..(.[!()3G^w]|.{7}|)|G\\ [[?C(].[-!)|w]|^P|^[^C|\\]* [?[CP(].[-<)|w]|^P|^[^C|\\]* ^..(.{7}|.[3Gw!^)]|)|G.?.?\) ^...[3w!G)]|^[^\\C|]*|G.?.?\) ^[^C\\|]+|G.\)|\.\)|w\^|^P|\...?] ^P|!.3|w\^|^[^C\\|]+|\.[)-](?!.!) \?[^w]*$$|[]C^]\w$|w.]|\w.\) $..\\|\?[^w]*$$|w\^|[]^C]\w$ • Correctness verified. – Martin Ender Nov 25 '14 at 10:58 • My solver immediately found a 32-character solution - a variation on the same theme. – Vi. Nov 25 '14 at 11:23 • @Vi. I'm expecting this to continue until someone breaks \?[^w$]*$ – Sp3000 Nov 25 '14 at 11:23 • So, nobody else want to post an answer? – Vi. Nov 25 '14 at 17:12 • Feel free, I'm observing. – hwnd Nov 25 '14 at 17:30 39. Perl flavour - 32 \w.\)|\?[^-]*$$|[]^C]\w$|w[+^]


Regex101 submission

Generated by the program. There are also 2 competing 32-character solutions.

The next answer has to match the following strings:

PPCG
^P
^[P^]P
[^?][PG]$(?<!\\..)(?!]).$
^[\w^]*$|!|]P|G]$!|[^?]P(CG|G..)? [^])]$|^\^?P|P.\].$
([.$?]|G\])$|^\^?P|\]P ([P.?]$|[]^]P|G\]$|CG) !|((G.|P|\.)$|[^?]P|CG)$
^[(!P]|G..$|]..\||[^?]P$
^.{3,23}[.-~]..$|[^P?][PG] ^..(.[!G)(3w^]|.{7}|)|$\?
\.\)|P[.$?]|w\^|^[^|C\\]*$|^P
^..(.[!)3G^w]|$)|\^.{7}$|G\)
\?[^w$]*$|[]^C]\w+|w\^|\|..\) \w.\)|\?[^-]*$$|[]^C]\w$|w[+^]  And fail on these strings: [PPCG] ^[P\^] [^\]]$
^\^?P
[^?][PG]$|<|PG ^[^\\|]*(\\\\)+[^\\|]*[^\]]$
^(.{,4}|.{9}|.{16,19}|.{5}P)$^[^?]*[PG]$|[?$].*$^[^[]P|]P|(G]|[.])$$
\..$|!|\|G|^[\^P]P|P\^|G.$...\^.P|^!|G]$$|w|<!|^\^?P
([^\\}<]{3}|][^]]|^).?[$PG]$
^(..[^^].{4,22}$|[^?]+\w)|2 ^(..[^^].{4,22}$|[^?]+\w)$|~ ^..(.[!()3G^w]|.{7}$|$)|G\\ [[?C(].[-!)|w]|^P|^[^C|\\]*$
[?[CP(].[-<)|w]|^P|^[^C|\\]*$^..(.{7}$|.[3Gw!^)]|$)|G.?.?\) ^...[3w!G)]|^[^\\C|]*$|G.?.?\)
^[^C\\|]+$|G.\)|\.\)|w\^|^P|\...?] ^P|!.3|w\^|^[^C\\|]+$|\.[)$-](?!.!) \?[^$w]*$|[]C^]\w|w.]|\w.\)$..\\|\?[^w$]*$|w\^|[]^C]\w  • Correctness verified. – Martin Ender Nov 25 '14 at 18:05 41. PCRE - 36 []^C]\w|\w.\)|-$|w[+^]|\?[^w$]*$ Tested on Regex101 The next answer has to match the following strings: PPCG ^P ^[P^]P [^?][PG] (?<!\\..)(?!]). ^[\w^]*|!|]P|G]$$!|[^?]P(CG|G..)?$
[^])]$|^\^?P|P.\]. ([.?]|G\])$$|^\^?P|\]P$
([P.$?]$|[]^]P|G\]$|CG)$
!|((G.|P|\.)$|[^?]P|CG) ^[(!P]|G..|]..\||[^?]P ^.{3,23}[.-~]..$$|[^P?][PG]$
^..(.[!G)(3w^]|.{7}$|$)|$\? \.\)|P[.?]|w\^|^[^|C\\]*|^P ^..(.[!)3G^w]|)|\^.{7}|G\) \?[^w]*$$|[]^C]\w+$|w\^|\|..\)
...\^.P|^!|G]$|w|<!|^\^?P ([^\\}<]{3}|][^]]|^).?[PG] ^(..[^^].{4,22}$|[^?]+\w)$|2 ^(..[^^].{4,22}$|[^?]+\w)|~ ^..(.[!()3G^w]|.{7}|)|G\\ [[?C(].[-!)|w]|^P|^[^C|\\]* [?[CP(].[-<)|w]|^P|^[^C|\\]* ^..(.{7}|.[3Gw!^)]|)|G.?.?\) ^...[3w!G)]|^[^\\C|]*|G.?.?\) ^[^C\\|]+|G.\)|\.\)|w\^|^P|\...?] ^P|!.3|w\^|^[^C\\|]+|\.[)-](?!.!) \?[^w]*$$|[]C^]\w$|w.]|\w.\) $..\\|\?[^w]*$$|w\^|[]^C]\w$[]^C]\w$|\w.\)|w[[+^]|\?[^w$]*$ • Correctness verified. – Martin Ender Nov 27 '14 at 14:01 13. PCRE flavor - 20 [^])]$|^\^?P|P.\].$


The next answer has to match the following strings:

PPCG
^P
^[P^]P
[^?][PG]$(?<!\\..)(?!]).$
^[\w^]*$|!|]P|G]$!|[^?]P(CG|G..)? [^])]$|^\^?P|P.\].$


And fail on these strings:

[PPCG]
^[P\^]
[^\]]$^\^?P [^?][PG]$|<|PG
^[^\\|]*(\\\\)+[^\\|]*[^\]]$^(.{,4}|.{9}|.{16,19}|.{5}P)$

• The previous answer (mine) has not been verified yet, so I hope it's valid so you don't lose your work. – NinjaBearMonkey Nov 13 '14 at 23:52
• @hsl taken care of that. user23013, please watch out for that next time ;) – Martin Ender Nov 13 '14 at 23:54
• Correctness verified. – Martin Ender Nov 13 '14 at 23:55

17. Python flavor - 21

^[^[]P|]P|(G]|[.])$ Tested on Regex 101. The next answer has to match the following strings: PPCG ^P ^[P^]P [^?][PG] (?<!\\..)(?!]). ^[\w^]*|!|]P|G]$$!|[^?]P(CG|G..)?$
[^])]$|^\^?P|P.\]. ([.?]|G\])$$|^\^?P|\]P$
([P.$?]$|[]^]P|G\]$|CG)$


And fail on these strings:

[PPCG]
^[P\^]
[^\]]$^\^?P [^?][PG]$|<|PG
^[^\\|]*(\\\\)+[^\\|]*[^\]]$^(.{,4}|.{9}|.{16,19}|.{5}P)$
!|[^?]P(CG|G..)?$[^])]$|^\^?P|P.\]. ([.?]|G\])$$|^\^?P|\]P$([P.$?]$|[]^]P|G\]$|CG)$!|((G.|P|\.)$|[^?]P|CG)  And fail on these strings: [PPCG] ^[P\^] [^\]] ^\^?P [^?][PG]|<|PG ^[^\\|]*(\\\\)+[^\\|]*[^\]] ^(.{,4}|.{9}|.{16,19}|.{5}P) ^[^?]*[PG]|[?].*$$
(?<!\\..)(?!]).$^[\w^]*$|!|]P|G]$!|[^?]P(CG|G..)? [^])]$|^\^?P|P.\].$([.$?]|G\])$|^\^?P|\]P ([P.?]$|[]^]P|G\]$|CG) !|((G.|P|\.)$|[^?]P|CG)$ And fail on these strings: [PPCG] ^[P\^] [^\]]$
^\^?P
[^?][PG]$|<|PG ^[^\\|]*(\\\\)+[^\\|]*[^\]]$
^(.{,4}|.{9}|.{16,19}|.{5}P)$^[^?]*[PG]$|[?$].*$^[^[]P|]P|(G]|[.])$$
\..$|!|\|G|^[\^P]P|P\^|G.$ • Correctness verified. – hmatt1 Nov 14 '14 at 4:57 20. PCRE flavour - 27 ...\^.P|^!|G]$$|w|<!|^\^?P


Tested on Regex101.

The next answer has to match the following strings:

PPCG
^P
^[P^]P
[^?][PG]$(?<!\\..)(?!]).$
^[\w^]*$|!|]P|G]$!|[^?]P(CG|G..)? [^])]$|^\^?P|P.\].$
([.$?]|G\])$|^\^?P|\]P ([P.?]$|[]^]P|G\]$|CG) !|((G.|P|\.)$|[^?]P|CG)$


And fail on these strings:

[PPCG]
^[P\^]
[^\]]$^\^?P [^?][PG]$|<|PG
^[^\\|]*(\\\\)+[^\\|]*[^\]]$^(.{,4}|.{9}|.{16,19}|.{5}P)$
(?<!\\..)(?!]).$^[\w^]*$|!|]P|G]$!|[^?]P(CG|G..)? [^])]$|^\^?P|P.\].$([.$?]|G\])$|^\^?P|\]P ([P.?]$|[]^]P|G\]$|CG) !|((G.|P|\.)$|[^?]P|CG)$^[(!P]|G..$|]..\||[^?]P$ And fail on these strings: [PPCG] ^[P\^] [^\]]$
^\^?P
[^?][PG]$|<|PG ^[^\\|]*(\\\\)+[^\\|]*[^\]]$
^(.{,4}|.{9}|.{16,19}|.{5}P)$^[^?]*[PG]$|[?$].*$^[^[]P|]P|(G]|[.])$$
\..$|!|\|G|^[\^P]P|P\^|G.$...\^.P|^!|G]$$|w|<!|^\^?P


27. PCRE Flavor - 27

^..(.[!()3G^w]|.{7}$|$)|G\\


Demo. The previous answer clearly works, so... thanks? :)

The next answer has to match the following strings:

PPCG
^P
^[P^]P
[^?][PG]$(?<!\\..)(?!]).$
^[\w^]*$|!|]P|G]$!|[^?]P(CG|G..)? [^])]$|^\^?P|P.\].$
([.$?]|G\])$|^\^?P|\]P ([P.?]$|[]^]P|G\]$|CG) !|((G.|P|\.)$|[^?]P|CG)$
^[(!P]|G..$|]..\||[^?]P$
^.{3,23}[.-~]..$|[^P?][PG] ^..(.[!G)(3w^]|.{7}|)|$\?


And fail on these strings:

[PPCG]
^[P\^]
[^\]]$^\^?P [^?][PG]$|<|PG
^[^\\|]*(\\\\)+[^\\|]*[^\]]$^(.{,4}|.{9}|.{16,19}|.{5}P)$
^[^?]*[PG]$|[?$].*$^[^[]P|]P|(G]|[.])$$\..$|!|\|G|^[\^P]P|P\^|G.$...\^.P|^!|G]$$|w|<!|^\^?P ([^\\}<]{3}|][^]]|^).?[$PG]$^(..[^^].{4,22}$|[^?]+\w)|2 ^(..[^^].{4,22}$|[^?]+\w)$|~
^..(.[!()3G^w]|.{7}$|$)|G\\

• Correctness verified. – Martin Ender Nov 14 '14 at 20:54

33. Python flavour - 30

^...[3w!G)]|^[^\\C|]*$|G.?.?\)  Tested on Regex101 Originally I had the 30 char [.!w].[]?3P]|^P|^[^C|\\]*$|\?< for the previous set, but I took too long trying to find a 29 and hwnd inadvertedly ruled out my submission.

So instead I mashed together two common themes we've had so far, just for fun :)

(?<!\\..)(?!]).$^[\w^]*$|!|]P|G]$!|[^?]P(CG|G..)? [^])]$|^\^?P|P.\].$([.$?]|G\])$|^\^?P|\]P ([P.?]$|[]^]P|G\]$|CG) !|((G.|P|\.)$|[^?]P|CG)$^[(!P]|G..$|]..\||[^?]P$^.{3,23}[.-~]..$|[^P?][PG] ^..(.[!G)(3w^]|.{7}|)|$\? \.\)|P[.$?]|w\^|^[^|C\\]*$|^P ^..(.[!)3G^w]|$)|\^.{7}$|G\)  And fail on these strings: [PPCG] ^[P\^] [^\]]$
^\^?P
[^?][PG]$|<|PG ^[^\\|]*(\\\\)+[^\\|]*[^\]]$
^(.{,4}|.{9}|.{16,19}|.{5}P)$^[^?]*[PG]$|[?$].*$^[^[]P|]P|(G]|[.])$$
\..$|!|\|G|^[\^P]P|P\^|G.$...\^.P|^!|G]$$|w|<!|^\^?P
([^\\}<]{3}|][^]]|^).?[$PG]$
^(..[^^].{4,22}$|[^?]+\w)|2 ^(..[^^].{4,22}$|[^?]+\w)$|~ ^..(.[!()3G^w]|.{7}$|$)|G\\ [[?C(].[-!)|w]|^P|^[^C|\\]*$
[?[CP(].[-<)|w]|^P|^[^C|\\]*$^..(.{7}$|.[3Gw!^)]|$)|G.?.?\) ^...[3w!G)]|^[^\\C|]*$|G.?.?\)

• Correctness verified. – Martin Ender Nov 24 '14 at 16:00

34. Perl flavour - 34

(?<!\\..)(?!]).$^[\w^]*$|!|]P|G]$!|[^?]P(CG|G..)? [^])]$|^\^?P|P.\].$([.$?]|G\])$|^\^?P|\]P ([P.?]$|[]^]P|G\]$|CG) !|((G.|P|\.)$|[^?]P|CG)$^[(!P]|G..$|]..\||[^?]P$^.{3,23}[.-~]..$|[^P?][PG] ^..(.[!G)(3w^]|.{7}|)|$\? \.\)|P[.$?]|w\^|^[^|C\\]*$|^P ^..(.[!)3G^w]|$)|\^.{7}$|G\)  And fail on these strings: [PPCG] ^[P\^] [^\]]$
^\^?P
[^?][PG]$|<|PG ^[^\\|]*(\\\\)+[^\\|]*[^\]]$
^(.{,4}|.{9}|.{16,19}|.{5}P)$^[^?]*[PG]$|[?$].*$^[^[]P|]P|(G]|[.])$$
\..$|!|\|G|^[\^P]P|P\^|G.$...\^.P|^!|G]$$|w|<!|^\^?P
([^\\}<]{3}|][^]]|^).?[$PG]$
^(..[^^].{4,22}$|[^?]+\w)|2 ^(..[^^].{4,22}$|[^?]+\w)$|~ ^..(.[!()3G^w]|.{7}$|$)|G\\ [[?C(].[-!)|w]|^P|^[^C|\\]*$
[?[CP(].[-<)|w]|^P|^[^C|\\]*$^..(.{7}$|.[3Gw!^)]|$)|G.?.?\) ^...[3w!G)]|^[^\\C|]*$|G.?.?\)
^[^C\\|]+\$|G.\)|\.\)|w\^|^P|\...?]

• There is also another 34 variant, substationally different with the posted one. – Vi. Nov 25 '14 at 0:28
• Correctness verified. – Martin Ender Nov 25 '14 at 0:43