Code challenges that involve the use of regular expressions.
13
votes
9answers
978 views
Quinean Regex Tester
This challenge is pretty simple. As input, you take in a regular expression.
Then, you output a truthy/falsey of whether or not your source code matches the regular expression. It's that simple! Just ...
20
votes
2answers
417 views
Compile Regexes (By Substitution)
Your task is to compile regexes... by specifying a substitution for each character in a regex.
Regexes
The regexes support these
REGEX = (LITERAL REGEX / GROUP REGEX / STAR REGEX / ...
-3
votes
1answer
118 views
A regexp that does not match itself [closed]
Can you think of a regular expression that does not match itself?
26
votes
4answers
409 views
Reverse a regex
The Challenge
Given a valid regex, output a regex that that matches the same set of strings, but reversed.
The Task
This challenge uses the most basic regex operations: ^, $, ?, +, *, [], {}, |. ...
1
vote
0answers
63 views
Simple regex parser [duplicate]
Let's parse some regex. Not quite the regex you are used to, but the formal regular expressions taught in courses on automata theory. Wikipedia knows what I'm talking about.
We have four operations. ...
12
votes
2answers
391 views
ValiDate ISO 8601 by RX
Challenge
Find the shortest regex that
validates, i.e. matches, every possible date in the Proleptic Gregorian calendar (which also applies to all dates before its first adoption in 1582) and
does ...
12
votes
3answers
1k views
Is that word Feminine or Masculine?
Write a program or function that takes in a single string containing only lowercase a-z, and prints or returns a truthy value if the word is the feminine version of the thing it represents and a falsy ...
13
votes
8answers
2k views
Remove single line and multiline comments from string
Goal
Using the programming language of your choice, write the shortest program to eliminate comments from a string representing a C program.
Input
The string can be...
given as a function ...
3
votes
4answers
339 views
Words of centuries
I'd like to get a list of words that are strongly connected with a particular time epoch, for example, 19th century, 20th century and 21st century. I suspect that nobody used a word like "smartphone" ...
21
votes
2answers
721 views
Gotta Match Them All! Write a regex to match the original 151 Pokemon but no subsequent Pokemon
The original 151 Pokemon, in an array format suitable for initializers:
["Bulbasaur", "Ivysaur", "Venusaur", "Charmander", "Charmeleon", "Charizard", "Squirtle", "Wartortle", "Blastoise", "Caterpie", ...
39
votes
5answers
3k views
Adding Numbers with Regex
I want to try a new type of regex golf challenge, which asks you to solve nontrivial computational tasks with nothing but regex substitution. To make this more possible and less of a chore, you will ...
30
votes
16answers
3k views
Tips for Regex Golf
Similar to our threads for language-specific golfing tips: what are general tricks to shorten regular expressions?
I can see three uses of regex when it comes to golfing: classic regex golf ("here ...
-3
votes
1answer
112 views
Listing links from pages — with error handling
In my previous question Debunking Stroustrup's debunking of the myth “C++ is for large, complicated, programs only”, a lot of people complained that comparison with Stroustrup's program isn't fair, ...
143
votes
55answers
33k views
Debunking Stroustrup's debunking of the myth “C++ is for large, complicated, programs only”
Stroustrup has recently posted a series of posts debunking popular myths about C++. The fifth myth is: “C++ is for large, complicated, programs only”. To debunk it, he wrote a simple C++ program ...
18
votes
9answers
896 views
Sum the time durations
Challenge
Write the shortest code that can sum all the time durations that appear in the stdin. The program must only consider the strings that match with one of the following patterns and ignore the ...
24
votes
2answers
617 views
Partial Ordering of Regex Patterns
For the purpose of this challenge, we say that a regex pattern matches a string if the entire string is matched by the pattern, not just a substring.
Given two regex patterns A and B, we say that A ...
-2
votes
1answer
150 views
Algorithm for finding a regex for a list of “words” [closed]
I just discovered this website and was amazed. Somehow this challenge popped into my mind:
Provided a very long list of words; Write or describe an algorithm which finds a regex to match them all.
...
39
votes
42answers
4k views
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 ...
9
votes
2answers
439 views
Python: I wish I was PHP
There's an old story about a stonecutter who was never satisfied with what he was. He wished he could become the sun, and so he was. Blocked by the clouds, he wished to be - and became - a cloud. When ...
69
votes
39answers
8k views
Cops and Robbers: Regex Golf
Note: This challenge is now closed. Any future cops' submission will not be considered for the accepted answer. This is to ensure that no one can post a very simple regex in the future that only ...
12
votes
6answers
2k views
Interpret /// (pronounced 'slashes')
Because we can't get enough of esoteric language golfs, can we?
///—pronounced slashes—is a fun little language based on the s/// regex-replacement function of Perl fame. It contains only ...
69
votes
1answer
5k views
Regex that only matches itself
There are some pretty cool challenges out there involving regex (Self-matching regex, Regex validating regex)
This may well be impossible, but is there a regex that will ONLY match itself?
NOTE, ...
6
votes
1answer
524 views
Regex that matches any regex [duplicate]
Your task is to write a regular expression that matches any valid regular expression and no invalid expression.
You may pick any regex flavour for your answer, but you have to match regular ...
13
votes
2answers
1k views
Regex in reverse - decompose regular expressions
The Problem
I have a bunch of regular expressions that I need to use in some code, but I'm using a programming language that doesn't support regex! Luckily, I know that the test string will have a ...
9
votes
0answers
474 views
Complement a Regular Expression
Given a regular expression as input, output its complement. If the given regular expression matches a string, its complement should not match it, and the regex: (regex given)|(complement) should match ...
-1
votes
1answer
144 views
POSIX reg. exp to test the divisibility by 9
Write the shortest POSIX-form regular expression that matches only non-negative integers divisible by 9. The non-negative integer should be given in base 10.
21
votes
11answers
967 views
Cross-matching regular expressions
Your task here is to write two regular expressions, each of which matches the other one but does not match itself.
Both regular expressions should have this form:
/pattern/optional-flags
This is ...
3
votes
2answers
163 views
Reverse Regular expressions [closed]
The idea here is to write a little segment that will spit out regular expression patterns when given a string that matches them.
As you might have guessed, this will be a popularity contest, and I'll ...
3
votes
1answer
2k views
Match strings whose length is isolated prime
Isolated prime definition from Wikipedia:
An isolated prime is a prime number p such that neither p − 2 nor p + 2 is prime. In other words, p is not part of a twin prime pair. For example, 23 is ...
22
votes
4answers
2k views
Match strings whose length is a fourth power
Within the scope of this question, let us consider only strings which consist of the character x repeated arbitrary number of times.
For example:
<empty>
x
xx
xxxxxxxxxxxxxxxx
(Well, ...
16
votes
2answers
474 views
Singular or plural?
Here is a list of 30 English nouns in their singular and plural form. Your job is simply to write the shortest regular expression that matches all the nouns in one form and none in the other (easy, ...
0
votes
4answers
305 views
Regex - Match half of the strings
Okay, the challenge is that you have to write a regex that matches half of all strings.
Some rules to clarify:
For ANY string length(>0), if I permute all strings(of that length), exactly half of ...
55
votes
24answers
12k views
Shortest unmatchable regular expression
Your mission is to write the shortest valid regular expression that no string can match, empty string included.
Submissions must have this form ("literal notation"):
/pattern/optional-flags
...
3
votes
3answers
367 views
Regex for Finding Non-Radioactive Elements
Find the shortest regex that matches all non-radioactive elements and nothing else in the Periodic Table of Elements. This is the inverse of Regex for Finding Radioactive Elements
Radioactive ...
8
votes
3answers
399 views
Regex for Finding Radioactive Elements
Find the shortest regex that matches all radioactive elements and nothing else in the Periodic Table of Elements.
Radioactive Elements
...
22
votes
5answers
1k views
Regex Golf: Regions of Italy vs. States of USA
We've already got a meta-regex-golf problem as inspired by the xkcd comic
But, this regex golf looks fun, too! I want to distinguish between the states of the US and the regions of Italy. Why? ...
23
votes
4answers
4k views
Meta regex golf
In the spirit of this xkcd
Write a program that plays regex golf with arbitrary pairs of lists. The program should at least attempt to make the regex short, a program that just outputs ...
0
votes
2answers
2k views
Make a regex that matches certain binary numbers [closed]
Your task is to create a regular expression that matches most binary numbers with an even number of 0s and an odd number of 1s (e.g. "101100011").
The full criteria for the regex are:
matches 90% ...
8
votes
4answers
847 views
Generate regular expressions for matching natural numbers between `m` and `n`
The type of regular expression is PCRE.
Write a program that output a valid PCRE such that it matches all natural numbers between m and n and does not match anything else. No leading zeros are ...
3
votes
1answer
392 views
Convert Regexes
Suppose you have existing regexes you wish to compile using one of the submissions to Compile Regexes.
In as few characters as possible, write a program that:
accepts an existing regex as input, as ...
10
votes
2answers
706 views
Compile Regexes
In this task you have to write a program that reads a regular expression and generates another program that outputs whether an input string is accepted by that regular expression. The output must be a ...
12
votes
3answers
2k views
Self-matching regex
Write a non-trivial regex that matches itself.
For example, #.*$ will match a comment outside of a string in python until the end-of-line, and also matches itself in perl regex syntax.
Rules:
The ...
64
votes
7answers
23k views
Hard code golf: Regex for divisibility by 7
Matthias Goergens has a 25,604-character (down from the original 63,993-character) regex to match numbers divisible by 7, but that includes a lot of fluff: redundant parentheses, distribution ...
4
votes
2answers
281 views
Negative Regexp
Write the shortest function that takes one string, and returns a regular expression that matches anything EXCEPT the input string, in parenthesis. Escape necessary characters like Perl quotemeta.
...
10
votes
1answer
979 views
Implement PCRE in your language.
Note: After trying this myself, I soon realized what a mistake this was. Therfore, I am modifying the rules a bit.
The minimum required functionality:
Character classes (., \w, \W, etc.)
...
15
votes
12answers
1k views
Implement glob Matcher
Implement a function of pattern and string to be matched, return true if the pattern matches the WHOLE string, otherwise false.
Our glob pattern syntax is:
? matches any one character
+ matches one ...
15
votes
4answers
21k views
Shortest URL regex match in JavaScript
Create the shortest regular expression that will roughly match a URL in text when run in JavaScript
Example:
"some text exampley.com".match(/your regular expression goes here/);
The regular ...
