Best possible answers collected so far for [Regex golf](http://regex.alf.nu/). === WARNING: SPOILERS ===

regex_golf.md

See Also:

• HN Post
• Regex Golf Answers (Gist)
• Best known Regex Golf solutions (Gist)
• Regex Golf (reddit)

Normal

Level	Score	Regex	Credit
Warmup	207	foo
Anchors	208	k$
Ranges	202	^[a-f]*$
Backrefs	201	(...).*\1	gorhill (HN)
Abba	195	^(?!.*(.)\1)|ef	BeniaminK (GH)
A man, a plan	177	^(.)[^p].*\1$	hyp0 (HN)
Prime	286	^(?!(..+)\1+$)	josephlord (HN)
Four	199	(.)(.\1){3}	chrismorgan (HN) / MereInterest (HN)
Order	199	^.{5}[^e]?$	ekke (HN)
Triples	596	00($|3|6|9|12|15)|4.2|.1.+4|55|.17	alexandrosm (GH)
Glob	397	ai|c$|^p|[bcnrw][bnopr]	nwellnhof (HN)
Balance	454	.{37}|^(<(..(?!<.>$))*>)*$	Davidebyzero (GH)
Powers	93	^(?!(.(..)+)\1*$)	plby (GH)
Long count	256	((.+)0\2+1){8}	Davidebyzero (GH)
Alphabetical	317	.r.{32}r|a.{10}te|n.n..	alexandrosm (GH)
Powers 2	88	^(?!((xxx)+x|xx|)\1*$)	muxrwc (GH)
Total	4075
Subtraction	180	^(.+)(.+) - \1 = \2$	jonathanmorley (GH)
Typist	181	^[adresbtcfxzgvw]+$	jonathanmorley (GH)

Hard Mode

Level	Score	Regex	Credit
Warmup	207	foo
Anchors	206	ick$	Davidebyzero (GH)
Ranges	202	^[a-f]*$
Backrefs	201	(...).*\1	gorhill (HN)
Abba	193	^(?!.*(.)(.)\2\1)	chingjun (HN) / josephlord (HN)
A man, a plan	150	^(.?)(.?)(.?)(.?)(.?)(.?).?\6\5\4\3\2\1$	jonathanmorley (GH)
Prime	284	^(?!(xx+)\1+$)xx	Davidebyzero (GH)
Four	199	(.)(.\1){3}	chrismorgan (HN) / MereInterest (HN)
Order	156	^a*b*c*d*e*f*g*h*i*j*k*l*m*n*o*p*q*r*s*t*u*v*w*x*y*z*$	Davidebyzero (GH)
Triples	524	(?=((.*?[147]){3})*((.*?[147]|){2}))(?=((.*?[258]){3})*((.*?[258]|){2}))^.*$(\3\7|(?!\3|\7)\4\8|(?!\4|\8))	teukon (GH)
Glob	297	ai|c$|^p|[bcnrw][bnopr]	nwellnhof (HN)
Balance	443	^(<(<(<(<(<(<(<>)*>)*>)*>)*>)*>)*>)*$	gkucmierz (GH)
Powers	93	^(?!(.(..)+)\1*$)	plby (GH)
Long count	239	^((?=(\S*)0).{4} (?=\2[1]))+1+$	Davidebyzero (GH)
Alphabetical	282	^(?!.*\b(.*)(e|(n|r|(s|t))).* \1(a|(?!\3)[en]|(?!\4)[rs]))	teukon (GH)
Powers 2	-12	^(?!((xxx)+x|xx|)\1*$)	muxrwc (GH)
Total	3664
Subtraction	180	^(.+)(.+) - \1 = \2$	jonathanmorley (GH)
Typist	180	^[adresbtcfxzgvwq]+$	jonathanmorley (GH)

I can't figure out how you're supposed to cancel formatting inline; any pointers?

Glob (336 - hard)

^(.*)(\*?)(.*)(\*?)(.*)(\*?)(.*) .* \1((?!\2).+|\2)\3((?!\4).+|\4)\5((?!\6).+|\6)\7$

Powers 2 (86 - hard)

^(?!((...)+..?|..|)\1*$)

It seems like

^(?!((...)*..?|)\1*$)

should work, but it doesn't match anything and I can't figure out why.

Note: the following are obsoleted by https://gist.github.com/Davidebyzero/9090628, so I won't bother reporting any more solutions, but I'll leave these here anyways since they represent solutions I developed myself or tweaks/optimizations I made to others' solutions.

Subtraction (182 - both)

^(.*)(.*)- \2= \1$

Addition (167 - both)

^(.*)(.+) .(.+)(.*) =\3\1 . \2\4$

or

^(.+)(.*) .(.*)(.+) =\3\1 . \2\4$

or

^(.+)(.*) .(.+)(.*) =\3\1 . \2\4$

or

^(.+)(.*) .(.+)(.+) =\3\1 . \2\4$

Or if you're boring, you can just do this 👅

^(.*)(.*) .(.*)(.*) =\3\1 . \2\4$

Anyway (168 - normal; 68 - hard)

^[aeiouy]?(.[aeiouy])+[^aeiou]?$

This works for normal mode, but fails the extended cases for hard. I feel like I'm missing something obvious here.

Tic-tac-toe (142 - normal; 42 - hard)

(([OX])\2\2|([OX])...\3...\3|([OX])....\4....\4)

This doesn't match "OXX OX. XO.", but that doesn't look like a won/winnable tic-tac-toe game.

Edit: My current totals, after reading through a lot of comments, are: default levels: 4075 (normal), 3801 (hard); bonus levels: 1736 (normal), 1731 (hard). As far as I can tell, these are the best possible scores given currently known regexes.

Abba's max is 196:
^(?!(.)+\1)|ef

Anyway (191 - HARD) based on @Dinoguy1000:
^[aeiouy]?([^aeiou][aeiouy])*[^aeiou]?$

Typist in normal (185): ^[a-grstvwxz]+$

Powers 2 (87 - hard):
^((?=(x_)\2\2$)\2\2)_x$

Tic-tac-toe (N:153) : XXX|OOO|X...X...X|O...O...O|X..X..X|X....X....X
Tic-tac-toe (H:133) : XXX|OOO|X...X...X|O...O...O|X..X..X|O..O..O|X....X....X|O....O....O

Based on @zeshanlb's last answer
Tic-tac-toe (N:156) : XXX|OOO|([OX])...\1...\1|X..X..X|X....X....X
Tic-tac-toe (H:142) : XXX|OOO|([XO])...\1...\1|X..X..X|O..O..O|([XO])(....\2){2}

Powers 2 (86) ^(?!((xxx)+xx?|xx)\1*$). Hard mode.

Correct Powers 2: ^(?!(|xx|xx?(xxx)+)\1*$) 86
Tic-tac-toe: ([OX])\1\1|([OX])..\2..\2|([OX])...\3...\3|([OX])....\4....\4 139 Hard mode
Addition: ^(.*)(.*).(.*)(.*) .\3\2. \1\4$ Both 169

Excuse me, but whoever got 180 points on Typist, can't I just use a few ranges to improve that? ^[a-gq-tvwxz]+$
(sings while looking at keyboard) A, B, C, D, E, F, G. H, I, J, K, LMNOP. Q, R, S. T, U, V. W, X, Y, Z.
Sorry. I just had to tell you that you could get five more points. 😄 👍

EDIT: You had 180, not 181. Sorry.

Glob - Hard (341): ^(.*)(?=.*( .* \1))(\2|\*(.*)(\2.+\4|\*(.*)(\2.+\4.+\6|\*(.*)\2.+\4.+\6.+\8)))$
Long Count - Hard (245): ^((\d*)01* (?=\2(1)))*1*$
Powers 2 - Hard (76): x{16385}|^(?!(xx(xx)?(xxx)*)\1*$)x
Subtraction - Normal, Subtraction - Hard (182): ^(.+)(.+)- \2= \1
Typist - Normal, Typist - Hard (189): ^[^h-puy]*$

No-one thought of these yet?
Tic-tac-toe: (Hard or robust) (168) (X|O)(\1|..(\1|.\1.|..\1..)..)\1
Powers 2: (Hard/robust) (89) ^((x+)\2(?=\2$)|x$)+$

Addition (robust) (177): ^(.*)(.*)(.*) = \3\2\1$ (credit to Davidebyzero)
Tic-tac-toe (robust) (169): (\w)(\1|..(\1|.\1.|..\1..)..)\1 (nice work micsthepick!)

Each of the bonus problems can be done with fewer than 40 characters. Most can be done using no more than 30 characters.

Any idea about this https://alf.nu/RegexGolf#accesstoken=Da3Q/rKFFqZwSic2o5Rt ?

It never ends – $ not allowed

Match all of these…
✔fu
✔tofu
✔snafu
and none of these…
✕futz
✕fusillade
✕functional
✕discombobulated

For It never ends - $ not allowed:
u\b

A man, a plan: ^(.)(.).*\2\1$

Abba: ^(?!(.)+\1)|.u

I've updated Best known Regex Golf solutions. The current Classic level set is fully covered. It's now in table format, including full credits and date-time stamps, a history of gradual improvements for most of the levels, and some extra bonus information.

I have intentionally not updated the Teukon level set solutions compilation, nor posted one for Holiday, as with the release of functioning high score lists in the newly brought back Regex Golf site, to do so would further taint the high scores with people who simply Google it and copy the solutions. This is not an ideal situation by any means, as I'd really like for everyone to be able to benefit from this knowledge if they so desire, but given the way the on-site high score lists currently function, I see no alternative. Having date-time stamps in the on-site high score lists would be a good start towards fixing this problem.

Subtraction ^(x+)(.+)- \2= \1$, no full space

New level: It never ends – $ not allowed
3 chars: u\b