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# Questions tagged [code-challenge]

A code challenge is a competition for creative ways to solve a programming puzzle with an objective winning criterion not covered by other scoring tags (e.g. code-golf).

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16 votes
2 answers
1k views

### Fast leap year check

The task is to find parameters that make a fast leap year check correct for the widest range of years. We assume the Proleptic Gregorian calendar, which extends the Gregorian calendar backward from ...
• 429
4 votes
8 answers
2k views

### Convert 8 Bit brainfuck to 1 bit Brainfuck / Boolfuck

Goal Input is a Brainfuck program for 8 bit cells, output it for 1 bit cells. Explanation We all know Brainfuck, normally it uses 8 bit cells. But there are implementations where a cell is just 1 bit, ...
2 votes
2 answers
498 views

### Largest possible relative error

Output $20$ float64s with absolute value between 1 and 2 inclusive whose sum has the largest possible relative error. We can assume the true sum is not zero. The sum is to be computed from left to ...
• 3,233
16 votes
3 answers
2k views

### Find 10 float64s that give the least accurate sum

Input Integer $n > 1$ Output Ten 64 bit floating point numbers between $-n$ and $n$, inclusive, whose sum is the least accurate. Details and examples. These examples are not claimed to be ...
• 3,233
-3 votes
5 answers
253 views

### Create the characters you can write on a MacOS US English Keyboard (as another OS will read them)

Introduction This is a small challenge I came up with while trying to make some compact code for my younger brother to use. I don't think it's particularly interesting, but I believe it presents some ...
• 9
4 votes
9 answers
2k views

### nimi ale lon toki pona! (Every word in Toki Pona!)

"nimi ale lon toki pona" is a song by YouTuber jan Misali which lists 137 common words in the constructed language Toki Pona. This challenge is not a duplicate of "How high can you ...
• 1,431
7 votes
2 answers
273 views

### Convert maximum values to bit widths

Background The newest version of the C standard, C23, adds preprocessor macros like INT_WIDTH, ULONG_WIDTH, and ...
18 votes
3 answers
951 views

### Magical BF: BF code that works in two ways

Challenge In this challenge, we will use a language that is very similar to Brainfuck but slightly different. This variant of BF does not have any input and output commands; instead, it simply takes ...
• 78.2k
0 votes
2 answers
231 views

### The many ways to skin a cat [duplicate]

The well known cat command simply copies its stdin directly to stdout unchanged. But there are plenty of other commandline tools that exist... What other commands ...
-2 votes
2 answers
276 views

### Forward foo, reverse bar, but avoid dead code [closed]

So simple: Provide some code that outputs foo and with the reversed source outputs bar. But before you come up with something ...
• 2,660
5 votes
11 answers
1k views

### Print the banned characters based on the most common characters

This is an answer-chaining post, so in this challenge every answer (except the first answer) depends on the previous answer. The goal of this challenge is to output the restricted characters. The ...
• 4,225
20 votes
31 answers
3k views

### Restricted Meta-Cat

Your challenge, should you choose to accept it, is to write a program in a language of your choice that, when given a string (limited to printable ASCII) as input, outputs a new program in the same ...
• 9,301
4 votes
5 answers
786 views

### What is the smallest possible binary output you can generate

Here is a challenge: What is the shortest possible compiled program? Writing one line programs are fun, but they often lean on language libraries that get pulled into the final bits. How lean can you ...
• 157
16 votes
6 answers
4k views

• 11
3 votes
4 answers
1k views

### Write the smallest possible code in x86-64 to implement the "<=>" operator

Languages, such as C++, have introduced a new comparison operator: <=>. This operator returns -1, 0, or 1† when comparing two items together: −1 means the ...
• 189
19 votes
17 answers
2k views

### Approximate my atomic weight

Each element on the periodic table of the elements has an atomic weight. For example, boron (element 5) has an atomic weight of 10.81. Your challenge is to write a program which takes as input the ...
• 5,830
12 votes
3 answers
485 views

### ><> numbers metagolf

I struggle to easily encode big numbers in ><>. If only there was a program that could find the best way for me? What is ><> ...
• 13k
25 votes
56 answers
3k views

### Range of ASCII values

Your task Given a string, output the range of ASCII values. Example Let's say we have the string Hello. We get the ASCII values: ...
• 18.3k
40 votes
5 answers
5k views

### 50 digits of π in HQ0-9+-INCOMPUTABLE?

Background HQ0-9+-INCOMPUTABLE?! is a half-joke programming language introduced in Internet Problem Solving Contest 2011, Problem H. HQ9+ is an esoteric programming language specialized for certain ...
• 78.2k
3 votes
4 answers
876 views

### A multidimensional strategy challenge

The wizard is determined to pose the most challenging challenge yet for which he believes the previous solution techniques will not work. He decides to go multidimensional. If there is a number line ...
17 votes
11 answers
2k views

### Numbers vs. Strings: Language fitness challenge

inspired by thejonymyster's idea Rules This challenge is about finding languages that are very suitable for one task but quite the opposite in the other. The two tasks share a theme, but Task 1 is ...
• 78.2k
10 votes
1 answer
492 views

### Turing Machine that outputs pi

Turing Machine Preliminaries A Turing machine is specified by the following data A finite set of symbols S = $\{s_1,s_2,...\}$ A finite set of states M = $\{m_1,m_2,...\}$ A partially defined ...
• 201
26 votes
12 answers
3k views

### Write a program with the smallest width

Print or return the following text: Hello world! The quick brown fox jumps over a lazy dog. However, your submission will not be scored in bytes. Instead, ...
• 14.9k
5 votes
4 answers
615 views

### Strategy: The cunning cousin witch

The wizard has a cunning cousin who is a witch. She looks down on the wizard, regarding him and his puzzles as mathematically naive. On reading his latest puzzle, she scorned him for always asking ...
5 votes
2 answers
930 views

### Optimal strategy to defeat the wizard

In this game, you can look inside one box at a time chosen by you. When you do that, you can see how many coins there are in that box. The wizard has one last twist for you. At any point, you can ...
20 votes
12 answers
3k views

### Optimal strategy for wandering robots

If the agent is at the origin it always moves right when you choose it. The goal is to get one agent to 10. The cost is the sum of the square of the total number of moves (left or right) taken by each ...
6 votes
2 answers
301 views

### Case Conversion Polyglot

Your task is to write a program that performs case conversion from plain text, and other case formats, into one of the specified formats below. Inputs will be either plain lowercase text, or one of ...
• 24.3k
5 votes
7 answers
840 views

### Typo resistant pin codes [closed]

Background I was working on a system where for convenience (not security) people could use four digit codes to identify themselves. I figured this is something that may actually be useful in many real ...
• 1,971
5 votes
0 answers
259 views

### Find the best character arrangement

You want to write your English essay. However, all characters on your keyboard broke other than the arrow keys and the enter key. You want to find out how to place the characters so you can write your ...
• 10.6k
19 votes
11 answers
2k views

### Write a near crystalline program

A pristine program is a program that does not have any errors itself but will error if you modify it by removing any contiguous substring other than the entire program. A crystalline program is sort ...
• 99.6k
1 vote
1 answer
265 views

### Implement the slowest possible sorting algorithm that retains a fast best case [closed]

I have recently been on a quest to create really really slow sorting algorithms that make Bogosort seem like it is the best. The task is simple: Sort an array of integers in as long average time as ...
• 27
-12 votes
5 answers
387 views

### 12 with no 1234567890, but polyglot

This is my 12th question, so I thought of this idea. Goal: Output 12, with any preceding or trailing whitespace permitted In as many languages as possible (where different versions or flags count as ...
• 1,548
29 votes
21 answers
4k views

### Add a hidden language to a polyglot

Inspired/mostly copied but I don't think it's a dupe. Also Inspired. In this challenge, you will create polyglots that include all languages from previous answers, and another language which you won't ...
• 42k
6 votes
1 answer
683 views

### Irradiated Polyglots

Design a function or program that, when run normally, outputs the triangular numbers. However, when any single character is deleted, the program/function should not function in the original ...
• 1,357
5 votes
1 answer
191 views

### BitCycle Metagolf

Background BitCycle is a two-dimensional Turing-complete programming language involves moving bits around a playfield. Because I am too lazy to write BitCycle programs myself, you will be writing a ...
• 14k
27 votes
28 answers
4k views

### What's the Missing Code? (Cops)

Cops' Challenge Robbers' challenge here. It has now been four days since the challenge was posted so all new answers should be marked as non-competing in the title. These answers can still be cracked ...
• 1,155
3 votes
0 answers
191 views

### Calculate the probability of getting this hand in n tries [closed]

Imagine there is a card game where the primary objective of the game is to get 4 of one card in your hand. Game mechanics Each player starts of with 10 cards in their hand. The remaining 32 cards (...
• 227
4 votes
3 answers
278 views

### Find All Digitroot Cyclic Sequences With Length Greater Than One

Digital sum, DR, Digit root is the iterative process of summing digits of a number until you end up with a single digit root number: e.g. digit root of 12345 is 6 since 1 + 2 + 3 + 4 + 5 = 15 = 1+5. ...
• 195
3 votes
2 answers
283 views

### Implement constant-latency branchless multiplication efficiently

Modern hardware can perform multiplication very fast in a constant latency of 3~4 cycles. But some tiny chips for embedded environments sometimes lack hardware multiplication, which has to be emulated ...
• 2,375
10 votes
3 answers
1k views

### Build an optimizing Brainfuck compiler/interpreter

the goal Build an optimizing Brainfuck implementation. Whether it is a compiler, an interpreter, a JIT compiler, or whatever else is up to you. scoring A reference implementation (...
• 2,375
6 votes
3 answers
346 views

### 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 ...
• 71
13 votes
1 answer
606 views

### Longest infinite loop in 5 states

Challenge Statement The goal of this challenge is to build the 5 state Infinite Time Turing Machine that takes the longest to halt. Since Infinite Time Turing Machines can run for infinite time your ...
• 99.6k
6 votes
2 answers
308 views

### 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 ...
• 1,161