# Questions tagged [decision-problem]

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

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47k 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 ...
14k views

### Is this number evil?

Introduction In number theory, a number is considered evil if there are an even number of 1's in its binary representation. In today's challenge, you will be identifying whether or not a given number ...
4k views

### Is this number a repdigit?

Challenge A repdigit is a non-negative integer whose digits are all equal. Create a function or complete program that takes a single integer as input and outputs a truthy value if the input number ...
4k views

### Egg, sausage, bacon and spam (lovely spam!)

You are given four integers: $e,s,b\in\{0,1\}$ and $S\in \{0,1,2,4\}$, where $e,s,b,S$ stand for egg, sausage, bacon and spam respectively. Your task is to figure out whether the corresponding ...
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### Halting Problem for Simplified Hexagony

Introduction Decide whether a Hexagony program composed solely of the characters .)_|\/><@ will halt using least bytes. Challenge Hexagony is a language ...
2k views

### Drawing one-liner

CodeDrawing one-liner Teaser Behold this formidable drawing: Can you draw this in a single stroke? Give it a try. Can you do this one, now: Give it a try. How it works These "make this drawing ...
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 ...
506 views

### Are They Similar Polygons?

Task Given the x,y coordinates (coordinates are guaranteed to be integers) of the vertices of two simple polygons in clockwise or anti-clockwise order. Output a Truthy value if both the polygons are ...
2k views

### 10-pin bowling split spare

Bowling Bowling is a game where, essentially, each player gets 10 turns to: Take 2 attempts at knocking down 10 pins arranged in a triangle. between turns the pins are reset from the 1st to the 2nd ...
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 ...
2k views

### Can I join the music box?

The magic music box (MMB) This explains the motivation for the challenge, feel free to ignore. The magic music box is a word game played by a group of people, where one is the owner of the magic ...
3k views

### Is this number a hill number?

A hill number is a number that has the same digit in the first & the last, but that's not all. In a hill number the first digits are strictly increasing until the largest digit, and after the ...
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 ...
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### Simple Circular Words

A "simple circular" word is a word whose chords do not intersect. The chords of a word may be seen by laying out the alphabet in a circle, and then connecting the word's consecutive letters. ...
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!! ...
2k views

### In for a bumpy ride

Your task is to write a computer program or function that takes a list of positive integers of at least length 2 and determines if they are a "zigzag". A sequence is a zigzag if and only if the ...
2k views

### Check if all non-zero elements in a matrix are connected

Input: A matrix containing integers in the range [0 - 9]. Challenge: Determine if all non-zero elements are connected to each other vertically and/or horizontally. Output: A truthy value if all ...
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 ...
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 ...
4k views

### Do you make me up?

Introduction Every string has an "alphabet", composed of the characters that make it up. For example, the alphabet of $abcaabbcc$ is ${a, b,c}$. There are two operations you can do with alphabets:...
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) ...
7k views

### Is it a leap year?

This challenge is quite simple. You will take an input which will be a year from 1801 to 2400, and output if it is a leap year or not. Your input will have no newlines or trailing spaces: ...
4k views

### Is it a circumfix?

Introduction We all know prefixes and suffixes. But there are other types of affixes that exist too. Such as circumfixes, a type of affix that has two parts, one of which is a prefix and another of ...
2k views

### Check if simple regex matches string

A simple regex is either: _ (which matches the empty string) Any lowercase letter a to z (...
5k views

### Is this number triangular?

Challenge Given a positive integer, determine whether it is a triangular number, and accordingly output one of any two constant, distinct values. Definition A triangular number is a number that can ...
7k views

### Is this number a factorial?

The Task Given a natural number as input, your task is to output a truthy or falsey value based on whether the input is a factorial of any natural number. You can assume that the input number will ...
5k views

### Does the start equal the end?

The Task In this challenge, your task is to write a program or function which takes in a String and outputs a truthy or falsey value based on whether the first character and the last character of the ...
523 views

### Is this a valid input for this hardware?

The (slightly harder, but still easy) sequel of Generate input for this hardware. Background I have a hardware that has a 32-bit input register. The register has the following characteristics: The ...
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Related: Is this quadrilateral cyclic? Background A tangential quadrilateral is a quadrilateral which has an incircle: Examples include any square, rhombus, or a kite-like shape. Rectangles or ...
5k views

For the non-zero digits on a standard numpad 789 456 123 consider placing a chess knight at any digit and moving it around with any number of normal L-shaped ...
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, ...
380 views

### Integer Keys and Duplicates

Given a non-empty list/vector of positive integers, write a function to check the following conditions in as few bytes as possible. Take the first integer (the key, or k1) and check that the next k1 ...
3k views

### Is this platform game level winnable?

Given a level from a simple platform game, your task is to make a program or function to determine if a level is winnable. Platform game levels are 4 characters tall and any number of characters wide. ...
3k views

### Hermitian matrix?

Note that this challenge requires no handling or understanding of complex numbers. Given a non-empty square matrix where every element is a two-element (Re,Im) integer list, determine (giving any ...
2k views

### Connect Four Validator

Introduction Connect Four is a game where you attempt to get four in a row: horizontally, vertically, or diagonally. In this code golf, we will be trying to find who won, given a game board. There ...
5k views

### Divisibility test

Task Given two strictly positive integers n and d as input, determine whether n is evenly divisible by d, i.e., if there exists an integer q such that n = qd. You ...
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### 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 ...
925 views

### Is it a valid chess move?

Alternate name: ChessMoveQ Given a list of up to 32 elements, each consisting of 4 elements, and a second list with 4 elements, determine whether the move detailed ...
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### Can I sweep the mines?

Minesweeper is a popular puzzle game where you must discover which tiles are "mines" without clicking on those tiles. Instead, you click on nearby tiles to reveal the number of adjacent mines. One ...
1k views

### Determining the winner of a Chess game

Challenge Being someone who plays far too much chess in his spare time, I thought I'd set a code golf challenge inspired by the game of chess (with a software flavour), for those interested. The ...
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), ...
1k views

### Are the two sets equal

{}is the empty set. You may use () or [] if you choose. We aren't going to rigorously ...
168 views

### Compare Dowker Knotation

Dowker notation is a common way of representing mathematical knots. Dowker notation can be derived from a knot diagram in the following way (based on the description from the wikipedium): We will ...
260 views

### Is this board Latin-style?

Inspired by Flow Fit: Sudoku, a brand-new mobile puzzle game (as of Nov 2019). Background A Latin square is a square grid of side length $n$ filled with $n$ different symbols, where each row ...
544 views

### Play Big 2 by yourself, as fast as you can

Introduction Big 2 is a card game popular in East Asia and South East Asia, in which 4 players are dealt 13 cards each (ie, an equal division of a standard deck without jokers). The goal is to empty ...
1k views

### Can Alice win the game?

Can Alice win the game? The game's rules are as follows. First, a finite non empty set of positive integers $X$ is defined. Then, Alice and Bob take turns choosing positive integers, with Alice ...
2k views

### The strange ordering of Sharkovskii

Introduction In this challenge, we will be dealing with a certain ordering of the positive integers. The ordering goes like this: ...
1k views

### Is it rectilinear?

Today's challenge: Given an ordered list of at least 3 unique integer 2D points forming a polygon, determine if the resulting polygon is Rectilinear. A polygon is rectilinear if every interior ...