Regex, Paper, Scissors, Lizard, Spock

Question

Warm up: Regex, Paper, Scissors

This is the challenge I originally wanted to post, before realising that some very short solution exist. Nevertheless, it can be an interesting problem to think about in preparation for the actual challenge below.

Write three regexes R, P and S such that they match each other in a cyclic Rock, Paper, Scissors fashion. In particular, R matches S, S matches P and P matches R, but R doesn't match P, S doesn't match R and P doesn't match S. Here's a handy table:

Regex   Matches   Doesn't match
R       S         P
P       R         S
S       P         R

It doesn't matter what R, P and S do on any other inputs, including themselves.

Here, match just means that some (possibly empty) substring of the input is matched. The match does not need to cover the entire input.

The challenge: Regex, Paper, Scissors, Lizard, Spock

For this challenge, you'll solve a tougher version of the above problem, based on the RPS variant Rock, Paper, Scissors, Lizard, Spock (as popularised by The Big Bang Theory). In RPSLV, there are five different symbols, that beat each other in two cycles:

• Rock → Scissors → Lizard → Paper → Spock → Rock
• Rock → Lizard → Spock → Scissors → Paper → Rock

You should write five regexes R, P, S, L and V which mimic this structure when given to each other as input. Here is the corresponding table:

Regex   Matches   Doesn't match
R       L, S      V, P
L       V, P      S, R
V       S, R      P, L
S       P, L      R, V
P       R, V      L, S

Just to be clear, you should not match the string R, P, etc, but the other regexes. E.g. if your regex R is ^\w$ for example, then P and V have to match the string ^\w$, whereas S and L shouldn't.

Again, match just means that at least one (possibly empty) substring of the input is matched. The match does not need to cover the entire input. For example \b (word boundary) matches hello (at the beginning and at the end), but it doesn't match (^,^).

You may use any regex flavour, but please state the choice in your answer and, if possible, provide a link to an online tester for the chosen flavour. You may not use any regex features that let you invoke code in the flavour's host language (like the Perl flavour's e modifier).

Delimiters (like /regex/) are not included in the regex when given as input to another, and you cannot use modifiers that are outside of the regex. Some flavours still let you use modifiers with inline syntax like (?s).

Your score is the sum of the lengths of the five regexes in bytes. Lower is better.

It turns out to be a lot simpler to find a working solution to this problem than it may seem at first, but I hope that finding an optimal solution is quite tricky.

Answer 1

PCRE, 15 14 bytes

Rock:
B

Paper:
\b$

Scissors:
b|B.

Lizard:
\B.

Spock:
^\w

Answer 2

PCRE .NET, 35 32 bytes

-3 bytes thanks to Martin Ender

Rock:

([*?]$)

Paper:

[)$]$+

Scissors:

[+?]$.*

Lizard:

[+$]$.?

Spock:

[*)]$

The idea here is to match characters at the end of other regexes which are reserved regex characters, but stop being treated as such when inside a character class.

Answer 3

no fancy features, 35 30 bytes

5 bytes saved by Neil's idea which uses that ] needs no \.

This works for example with the python re module.

R='[SLR]]'
P='[RVP]]'
S='[PLS]]'
L='[PVL]]'
V='[SRV]]'

It searches for a ] preceded by a letter that indicates which rule it is.

Previous version used R='\[[RSL]' etc.

An earlier attempt with score 40 was using R='[SL]x|Rx' etc.

Answer 4

PCRE, 20 19

Rock

W

Paper

^\w

Scissors

^\W

Spock

w?\x57$

Lizard

[w]W?

Answer 5

20 bytes

R = 'R|VP'
L = 'L|RS'
V = 'V|LP'
S = 'S|RV'
P = 'P|LS'

Answer 6

JavaScript, 45 bytes

Another trivial solution.

R:
^R|^.[SL]
P:
^P|^.[RV]
S:
^S|^.[PL]
L:
^L|^.[PV]
V:
^V|^.[SR]

Answer 7

POSIX, 50 45 bytes

Rock
.{5}RP?V?
Paper
.{5}PS?L?
Scissors
.{5}SR?V?
Lizard
.{5}LR?S?
Vulcan (Spock)
.{5}VP?L?

Could be done shorter but the (hide matches after $) trick got used, so I'm looking for another way

The first 5 chars of each string are ignored when matching. So the effective target string simplifies to just X?Y?. None of them have any double letters because "?" is an ordinary char, so the last 4 chars when used as a regex have to match (null string). So the patterns collapse down to "contains 5 chars followed by the target letter": meaning chars 6-9 of the target must contain the target letter (the 5th char in each string)

Update: 35 byte version below, now!

Answer 8

PCRE, 65 bytes

This is a really trivial solution - and not very clever at all - but I'll try to golf it.

V:

(?#V).+[SR]\)

L:

(?#L).+[PV]\)

S:

(?#S).+[PL]\)

P:

(?#P).+[RV]\)

R:

(?#R).+[SL]\)

Essentially, each regex has an 'identifier', in the form of a comment, which tells the other regexes whether it should be matched or not.

Answer 9

Vanilla RE, 40 characters

Not the most concise or elegant solution but has a pleasing quasi-semantic visual structure!

[^r][sl]
[^p][vr]
[^s][lp]
[^l][pv]
[^v][rs]

Rock beats Scissors or Lizard
Paper beats Vulcan or Rock
Scissors beats Lizard or Paper
Lizard beats Paper or Vulcan
Vulcan beats Rock or Scissors

Answer 10

.NET, 50 bytes

In order they are R, P, S, L, V.

[^R]\^[SL]
[^P]\^[RV]
[^S]\^[PL]
[^L]\^[PV]
[^V]\^[SR]

Works by looking for the identifier group (for example, [^R]) in each of the other expressions.

Changing the expressions to ^R|\^[SL], or similar, seems to work but then it's a bit too similar to @dzaima's answer although it would get it to 45 bytes.

Answer 11

POSIX, 35 bytes

Rock
R?^[LS]
Paper
P?^[RV]
Scissors
S?^[LP]
Lizard
L?^[PV]
Vulcan (Spock)
V?^[RS]

A completely different way to "hide" behind a start/end symbol, so I feel OK about it :) I'm matching to start because "?" would always have to go between letter and end/$ if done the other way.

10 bytes less than my 1st solution, and conceptually simple which is a bonus I like.