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### Print X without X (cop's thread)

This is the cop's thread of a cops-and-robbers challenge. You can view the robber's thread here A pretty common beginner style question is to print some string, but there's a catch! You need to do it ...
21k views

### DISARM THE B.O.M.B.!

You have been hired for your tech knowledge as a Secret Agent's sidekick to ensure that the good guy can get his job done and the world can be saved. This is your last mission before retiring with a ...
17k views

### Eww, those bytes are gross

Write a program or function that, when given a string, filters out as many distinct bytes as it can and returns the cleaned string. However, since your program hates them, none of these bytes can be ...
3k views

### Quickly! Group together!

As of 27/12/20, the challenge is over as no new answers were posted on the 26th. With an astounding 55 points (and 21 answers), the winner is pppery! A quick shout out to the top 5 scorers as well: ...
3k views

### Replace twos with threes

Given a positive integer n write some code to take its prime factorization and replace all of its factors of 2 with 3. For ...
3k views

### Turing-Complete Language Interpreter

A challenge I thought that would be very cool is to make an interpreter for a Turing-complete language of your choosing. The rules are simple: You may use any language to create this interpreter ...
15k views

### Biggest Irreducible Hello World

Create a program that outputs Hello, World! The winner is the source code that is the biggest, subject to the constraint that it is irreducible For this challenge,...
3k views

### Tips for restricted source in Python

Just like code-golf, restricted-source pushes one to exploit quirks and hidden features of the Python language. We already have a place to collect all these tips for code-golf, those for restricted-...
2k views

### Concatenative counting

Your challenge is to write N snippets of code such that, when you concatenate the first K ≥ 1 together, they produce the number K. The higher N, the better. Here's the catch: you may not use any ...
2k views

### Find a Fixed Point

Given an integer $x_1$ and some black box function $f: ℤ → ℤ$ find a fixed point of $f$ in the sequence defined by $x_{k+1} := f(x_k)$. Details A value $x$ is said to be a fixed point of \\$...
3k views

### Minimal maximum byte for Turing Completeness

Summary We already have a challenge for the minimal number of characters for Turing completeness. But what about the minimal maximum byte? Challenge For a language of your choice, find a subset of ...
1k views

### Rearrangeable Code Bowling

Code-Bowling Challenge Write a program or function that produces the same output, no matter how you re-arrange the source code. (Output can't be an error) Pangram Scoring Your score is the amount ...
6k views

### Build a Turing *incomplete* language

The world is full of Turing-complete programming languages. Just about every useful language (and most useless ones) are Turing-complete. Some even became Turing-complete by accident. Often this is ...