Questions tagged [regular-expression]
Code challenges that involve the use of regular expressions.
99 questions
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Identify Redundant Regex
A redundant regular expression (regex) is defined here as a regex which has some amount of characters which can be removed while not affecting its functionality -- i.e. it matches the exact same set ...
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Enumerate all matches of a regex
related
For this challenge, we'll be using a simplified dialect of regular expressions, where:
A lowercase letter from a to z ...
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What is the shortest regular expression (REGEX) you can create for file extensions for image formats? [duplicate]
What is the shortest regular expression (REGEX) you can create for file extensions for all of the following image file formats (photographs, paintings, sketches, and drawings)?
...
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What is the shortest regex for the month of January in a handful of the world's languages?
What is the shortest regular expression equivilant to the following?
...
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Write a regex that would increment a 2-digit hexadecimal number
Your regex will receive a string of the form
!XX!
#<extra>
where X is any hexadecimal digit (0-9 and A-F capital letters ...
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Is it a bigger regex?
You are given two regexes and your task is to determine if the strings matched by the first regex are a subset of the strings matched by the second regex.
For this we are going to use a limited ...
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Generate Matching Regexes
Write a program that takes two lists of strings and generates a javascript regex that fully matches all the strings in the first list and matches none of the strings in the second list.
To be specific ...
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Convert Regex to Mask
From my CMC.
Given a regex and a non-empty printable ASCII text, return one bit per character in the text, indicating the positions of beginnings of non-overlapping matches, and also the positions of ...
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Give the minimum Levenshtein distance to a string that matches the regex
Your task, at the moment that you choose to accept it, is to write a program that, when given a string and a PCRE-regex, calculates the minimum Levenshtein distance to another string that matches the ...
user106435
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Generate the shortest regex to match these but not those [closed]
Challenge
Given two lists of strings where each string is of length 50 and each list is also of length 50 generate the shortest regex you can that fully matches all the strings in the first list and ...
- 1,161
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Recognize most smaller primes with a regex
This time, you are working on a regex. Your regex is meant to approximately full-match the base-10 representations of primes \$0 \le p < 1000\$, while ignoring any non-numeric string or composite ...
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Are We Fast And Furious? [closed]
There are currently nine feature length films in the core Fast & Furious/The Fast and the Furious media franchise, a series of films about bald men scowling and driving cars very fast. The names ...
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Generating minimal regular expression character classes
Background
Character classes are a standard way to indicate a set of characters to match in regular expressions. For example, the class [ab] matches a or b, ...
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Distinguish English and Spanish with regular expressions
The task is to to compete for the shortest regex (in bytes) in your preferred programming language which can distinguish between English and Spanish with minimum 60%...
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Resource for generating shortest regex given a list of strings
I'm looking for a program such that, given a finite list of strings, can find short regexes to match exactly all of them and nothing else.
Since there are multiple languages that express regexes ...
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Count regex matches
Your task
Given a simple regular expression, you have to count how many strings of length n have a match of length n with the ...
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Check if simple regex matches string
A simple regex is either:
_ (which matches the empty string)
Any lowercase letter a to z (...
user84442
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answer
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Duct Tape a Regex Decider
Your task is to create a program that determines whether a given string is a valid regular expression or not using code snippets sourced from sites on the StackExchange network.
For the purposes of ...
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Regex golf and ccTLDs, hooray!
Write a regex that only matches valid country code top level domains (ccTLDs). Your regex must match both the domains with the dot and without the dot (it must match tv and .tv). Any domain that is ...
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Print everything which a regular expression matches [duplicate]
Modern regular expressions (regexes) have many features (\d, {n,m}, \1, etc.), but to define ...
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Insert commas into numbers [closed]
Write a program that reads a string, and inserts commas to divide large numbers in groups of 3. i.e. 10000 => 10,000. It should 'fix' incorrectly formatted numbers as described below.
It must work ...
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Regex only base64 decoder [closed]
Write a regular expression substitution string which can base64 decode a string using only a regular expression engine built into the language. Eg:
...
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FreeChat Online [closed]
FreeChat Online
It is 1985, and you are a humble Russian potato farmer. Sadly, your glorious homeland is going through a time of crisis and it needs your help! The KGB, with the "assistance" ...
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The Binary Fences
Input:
An integer n in the range 2 <= n <= 10
A list of positive integers
Output:
Convert the integers to their binary ...
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Regular Expression to find a pangram [closed]
Awhile back I encountered a simple programming puzzle to determine whether a string was a pangram, or a perfect pangram. (Although it's worth noting that this particular challenge gave a different ...
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Complement of a Regex
For the purposes of this challenge, we define a postfix regex dialect with alphabet {1, 0} and the following operations:
1 and <...
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Regex for multiples of 9
It is easy to describe a finite state machine that recognizes multiples of 9: keep track of the digit sum (mod 9) and add whatever digit is accepted next. Such a FSM has only 9 states, very simple! By ...
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Create a regex to match a given range of integers in a given radix
Task
Write a program/function that, given three integers n,a,b prints a regular expression which matches all of the base-n integers from ...
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A regex to match three consecutive integers iff the third integer is the sum of the first two
Write a regular expression which matches a given string consisting of three non-negative, space-separated integers if and only if the last integer is the sum of the previous two. Answers may be for ...
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Regex: Match an egalitarian series
Introduction
I don't see many regex challenges on here, so I would like to offer up this deceptively simple one which can be done in a number of ways using a number of regex flavours. I hope it ...
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The greedy regex (cops)
This is the cops' post. The robbers' is here.
You make a program and a regex.
For most inputs, one of the following happens:
the regex doesn't match, and the program returns a falsey value
the regex ...
user58826
6
votes
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answers
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The greedy regex (robbers)
This is the robbers' post. The cops' is here.
Your challenge is to take a cop's post and find an input that the regex matches but the program returns a falsey value.
Once you have cracked a cop's ...
user58826
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Regex, Paper, Scissors, Lizard, Spock
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 ...
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Regular expression parser
This task is a classic programming task: Implement a regular expression parser. That is, write a program or function which takes a string describing a regular expression and a candidate string, and ...
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Regex that matches everything but itself
You must make a regex that matches everything except itself. For example, PPCG must not match PPCG, but must match everything ...
user58826
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Robbers: Crack the regex - Make a snake
This is the robber's thread. The cop's thread is here.
A snake matrix is a square matrix that follows this pattern:
3-by-3:
1 2 3
6 5 4
7 8 9
and 4-by-4:
...
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Cops: Make a regex - Make a snake
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 ...
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Find letter-similar words in a word list [closed]
(I am not sure that this is the best place to put this question, but I will give it a shot. Forgive me if it is improper. This is just a fun project with which I am tinkering and I am looking for ...
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Make a regex polyglot
Write a regex that works in at least 2 regex flavors (or versions), and match a different string in each flavor (or version) it is running in.
The strings to be matched in this challenge are the ...
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The codegolf object
Imagine this, we have an environment with a global scope containing just a single object, called codegolf. This object has a single child called ...
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Match the permutations!
Your challenge is to create a regex that matches every string permutation of itself, and nothing else. The match must also be case-sensitive.
So, for example, if your regex is:
...
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A regex to satisfy the grammar police (there vs. their vs they're)
We've all been burned by the grammar police on the internet. What we need is a regex that can be used in place of "there", "their", and "they're". This would shift burden of grammar parsing from the ...
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Match the Stack Exchange URLs
Prologue
After installing an anti-XSS browser extension, Stack Snippets suddenly stopped working all across the Stack Exchange network. I could no longer learn from Stack Overflow, see working demos ...
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HexaRegex: A Tribute to Martin Ender
Martin Ender recently hit 100K, and has come up with some pretty awesome languages. We're going to have a bit of fun with one of them, Hexagony (and a bit of regex for Retina)
As a brief overview, ...
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Is case sensitivity important? Part II: reality check
In this question Tom learned that, in general, there are many motivations to choose to include case sensitivity in his programming language, because the possible combinations for a variable name are ...
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Check if a pattern appears in a DNA sequence
In a project I am working on, I am checking to see if certain DNA sequences appear in certain genes in E. coli. I have written a program in Java that performs the below features. However, since I ...
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Shortest simple regex matching a binary word
Task
Define a simple regex as a non-empty regular expression consisting only of
characters 0 and 1,
grouping parentheses ...
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RegEx-golf: match all contents in a string
Your task is to write a RegEx that matches everything inside strings.
A string is defined as everything surrounded by (but not including) two unescaped ".
A ...
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Find the last three words of each paragraph if they are shorter than 20 characters in total
Based on my SO question, but more specifically:
Find a RegEx such that, given a text where paragraphs end with an empty line (or $ at the very end), match the up ...
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