Code Golf

Questions tagged [decision-problem]

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For challenges which involve deciding whether or not the input meets certain criteria, and outputting some data, representing that decision.

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342
votes
1answer
109k 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, ...
198
votes
295answers
46k views

Is this number a prime?

Believe it or not, we do not yet have a code golf challenge for a simple primality test. While it may not be the most interesting challenge, particularly for "usual" languages, it can be nontrivial in ...
154
votes
16answers
27k views

Is My Swipe Pattern Legal?

Most Android smartphones allow the user to use a swipe pattern to open their phone: Certain patterns are legitimate, and others are impossible. Given an input swipe pattern, return a truthy or falsy ...
144
votes
1answer
5k views

“KNOT” or “NOT”?

Write a program that processes an ASCII art representation of a tangled string and decides whether or not it can be untangled into a simple loop. The tangle is represented using the characters ...
104
votes
66answers
26k views

I'm a palindrome. Are you?

There have been a couple of previous attempts to ask this question, but neither conforms to modern standards on this site. Per discussion on Meta, I'm reposting it in a way that allows for fair ...
94
votes
109answers
15k views

Will it halt? (Cops)

This is the cops' thread. The robbers' thread is here. Your challenge is to make a program that runs forever without halting1, unless it gets a particular input or inputs2. If it receives that input, ...
92
votes
33answers
6k views

Would this string work as string?

Write a program that takes a single line string that you can assume will only contain the characters /\_‾. (That's forward and backward slash, underline and ...
80
votes
50answers
13k views

Detect MS Windows

Challenge Create a program that returns a truthy value when run on Microsoft Windows (for simplicity we'll stick with Windows 7, 8.1 and 10) and a falsey value when run on any other operating system (...
76
votes
84answers
10k views

Count of “a”s and “b”s must be equal. Did you get it computer?

In the popular (and essential) computer science book, An Introduction to Formal Languages and Automata by Peter Linz, the following formal language is frequently stated: mainly because this language ...
75
votes
37answers
12k views

Non-discriminating Programming

We say a string is non-discriminating if each of the string's characters appears the same number of times and at least twice. Examples "aa!1 1 !a !1" is non-...
73
votes
63answers
14k views

Is this relationship creepy?

According to this XKCD comic, there is a formula to determine whether or not the age gap in a relationship is "creepy". This formula is defined as: (Age/2) + 7 ...
72
votes
38answers
12k views

Am I a Rude Number?

For a while now, I've been running into a problem when counting on my fingers, specifically, that I can only count to ten. My solution to that problem has been to count in binary on my fingers, ...
68
votes
47answers
9k views

Magic the Gathering: Friends or Foes?

In the card game Magic: the Gathering there are five different colours, which represent loose affiliations of cards, White (W), Blue (...
67
votes
212answers
20k views

Is this even or odd?

Note: There is not been a vanilla parity test challenge yet (There is a C/C++ one but that disallows the ability to use languages other than C/C++, and other non-vanilla ones are mostly closed too), ...
67
votes
46answers
7k views

Is it a Cyclops number? “Nobody” knows!

Task: Given an integer input, figure out whether or not it is a Cyclops Number. What is a Cyclops number, you may ask? Well, it's a number whose binary representation only has one ...
66
votes
7answers
5k views

Regex Golf: Verify a Sudoku Solution

Write a regex which matches any valid sudoku solution and doesn't match any invalid sudoku solution. The input is an unrolled version of the sudoku, i.e. there are no line delimiters. E.g. the ...
65
votes
11answers
3k views

Only Even Bytes

The scenario Lately you have been noticing some strange behavior with your favorite text editor. At first it seemed that it was ignoring random characters in your code when writing to disk. After a ...
64
votes
82answers
12k views

Golf all the 16 logic gates with 2 inputs and 1 output!

For example, the gate A and B is a logic gate with 2 inputs and 1 output. There are exactly 16 of them, because: each logic gate takes two inputs, which can be ...
64
votes
42answers
5k views

Check if words are isomorphs

Two words are isomorphs if they have the same pattern of letter repetitions. For example, both ESTATE and DUELED have pattern <...
60
votes
18answers
4k views

There are two new sheriffs in town – Identifying DJMcMego pairs!

We have some new sheriffs moderators in town, Mego and DJMcMayhem. We need a challenge to properly honour them for their new positions, so there we go. Here's something that has caught my attention ...
58
votes
77answers
6k views

Is the number binary-heavy?

An integer is binary-heavy if its binary representation contains more 1s than 0s while ignoring leading zeroes. For example 1 is ...
58
votes
38answers
4k views

Write the shortest self-identifying program (a quine variant)

Write a program that will generate a "true" output iff the input matches the source code of the program, and which generates a "false" output iff the input does not match the source code of the ...
58
votes
9answers
8k views

Is my prison secure?

Your challenge is given an input of a prison layout to work out whether any of the prisoners can escape. Input Input may be in any reasonable format such as a string, array, array of arrays etc. The ...
56
votes
32answers
5k views

Are the brackets fully matched?

You must write a program or function that takes a string of brackets and outputs whether or not that string is fully matched. Your program should print a truthy or falsy value, and IO can be in any ...
54
votes
22answers
3k views

Dennis numbers 2.0

PPCG user and elected mod, @Dennis just became the second ever user to earn over 100k rep! This is a totally original idea, that I did not get from anybody else, but let's make a challenge based off ...
54
votes
10answers
3k views

Surrounded Countries

Countries own a series of territories on a 1D world. Each country is uniquely identified by a number. Ownership of the territories can be represented by a list as follows: ...
53
votes
47answers
13k views

Is my OS 32-bit or 64-bit?

It's not too important anymore, but occasionally somebody needs to know. Here is a simple golf: Taking no user input, tell me if the computer on which the code is run is on a 64-bit operating system, ...
53
votes
73answers
7k views

Test a number for narcissism

A Narcissistic Number is a number which is the sum of its own digits, each raised to the power of the number of digits. For example, take 153 (3 digits): 13 + 53 + 33 = 1 + 125 + 27 = 153 1634: ...
52
votes
46answers
5k views

Is it a lipogram?

A lipogram is a block of words that omits a particular symbol. Right now, I am avoiding our fifth symbol of 26 that commonly show up. You should know by now what I am omitting. If not, look up "...
52
votes
75answers
9k views

Do n and n^3 have the same set of digits?

Given a number n (0 <= n <= 2642245), check if n and n3 have the same set of digits, and output a truthy or falsey value accordingly. For example, let's check the number 100. 1003 is 1000000. ...
52
votes
15answers
4k views

Tasteless and other bugs

Some versions of the standard Android calculator app allow you to press a key, like 'sin' and then the 'del' key to make it 'si'. Probably just a bug which they can't be bothered with removing. The ...
51
votes
18answers
4k views

Can my 4-note music box play that song?

I have a crank-operated music box that can play a series of four notes. When I turn the crank, it plucks one of four strings, depending on the position of the crank and the direction of the turn. When ...
50
votes
16answers
5k views

Code (Mini) Golf

Given a side-view of a mini-golf course and the power of the swing, determine if the ball will make it into the hole. A course will be in this format: ...
49
votes
61answers
9k views

Am I a Fibonacci Number?

Your Task: Write a program or function to check if a number that is inputted is a Fibonacci number. A Fibonacci number is a number contained in the Fibonacci sequence. The Fibonacci Sequence is ...
49
votes
27answers
7k views

Check if computer is connected to the internet

Write a program which, according to whether the script has access to the internet, produces an output which is "Truthy/Falsey". You may try and connect to any existing site, at your own discretion (...
49
votes
6answers
6k views

Your car only turns right!

Introduction You have the misfortune of being stuck in a runaway car on an obstacle course. All of the car's features are non-responsive, save for the steering system, which is damaged. It can ...
48
votes
44answers
5k views

Detect heat waves

Background The Royal Netherlands Meteorological Institute defines a heat wave* as a series of at least 5 consecutive days of ≥25°C weather (“summery weather”), such that at least 3 of ...
48
votes
15answers
10k views

Is this Tic-Tac-Toe board valid?

Challenge Given a tic-tac-toe board in any format, determine if it is valid or not. If a board can be the result of a tic-tac-toe game, then it is valid. For example, this board is valid:X O X O X O ...
48
votes
31answers
4k views

Does it Lead or Follow?

In this challenge you are to write a program or function, that takes a string as input and outputs one of two possible values. We will call one of these values truthy and one falsy. They do not need ...
48
votes
8answers
4k views

Determine if a coin system is Canonical

The Cashier's Algorithm is an algorithm for making change in the minimal number of coins that works quite well for most currency systems. However like most greedy algorithms it is not without its ...
47
votes
77answers
9k views

Is it double speak?

In an earlier challenge I asked code golfers to produce strings which copy each character in a string. For example: TThhiiss iiss ddoouubbllee ssppeeaakk!! ...
47
votes
76answers
9k views

Is my triangle right?

Given a, b, c the length of the three sides of a triangle, say if the triangle is right-angled (i.e. has one angle equal to 90 degrees) or not. Input Three ...
47
votes
43answers
4k views

Is this a function?

Given a list of (key, value) pairs, determine whether it represents a function, meaning that each key maps to a consistent value. In other words, whenever two ...
46
votes
139answers
12k views

Will it halt? (Robbers)

This is the robbers' thread. The cops' thread is here. Your challenge is to crack a cop's submission by finding an input that makes it halt. You don't have to find out why, or all inputs that make it ...
46
votes
19answers
5k views

Lever Simulator 2015

Why a Simulator? Kids these days don't have the time nor the ambition to actually go and stack boxes on the see-saw or play around with balancing physical objects. This leaves lots of room in the ...
44
votes
66answers
6k views

It's Hip to be Square

Challenge So, um, it seems that, while we have plenty of challenges that work with square numbers or numbers of other shapes, we don't have one that simply asks: Given an integer ...
44
votes
48answers
7k views

Is this string a square?

A string is considered to be square if the following conditions are met: Each line has the same number of characters The number of characters on each line is equal to the number of lines. Your task ...
43
votes
19answers
3k views

Has My Pie Been Bisected?

Write a program or function that takes in a nonempty list of positive integers. You may assume it is input in a reasonable convenient format such as "1 2 3 4" or <...
42
votes
66answers
5k views

Is it a pangram?

Write a function or program that takes as its input a string and prints a truthy value if the string is a pangram (a sequence of letters containing at least one of each letter in the English alphabet) ...
42
votes
43answers
16k views

Shortest code to determine if a string is a palindrome

A palindrome is some string that is spelled the same way both backwards and forwards. For instance, 'Eva, can I stab bats in a cave?' is a palindrome (EVACANISTAB | BATSINACAVE) For this code golf, ...

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