# Questions tagged [cops-and-robbers]

For challenges which consist of two adversary (and asymmetric) sub-challenges.

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### Hashers and Crashers (Robbers)

This is the robbers thread of this cops and robbers challenge. The cops thread is here. Related, but hashes numbers instead of strings and uses a different scoring system. Definitions A hash collision ...
232 views

### Hashers and Crashers (Cops)

This is the cops thread of this cops and robbers challenge. The robbers thread is here. Related, but hashes numbers instead of strings and uses a different scoring system. Definitions A hash collision ...
619 views

### Magic OEIS formulae (Robbers' thread)

This is the robbers' thread. See the cops' thread here. In this cops and robbers challenge, the cops will be tasked with writing an algorithm that computes some function of their choice, while the ...
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725 views

### Magic OEIS formulae (Cops' thread)

This is the cops' thread. See the robbers' thread here. In this cops and robbers challenge, the cops will be tasked with writing an algorithm that computes some function of their choice, while the ...
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1k views

### (Robbers) Fast and Golfiest Season 1: The Lord of the Strings

Fast and Golfiest Robbers Thread Welcome to the first season of Fast and Golfiest, a cops-and-robbers challenge! I designed this challenge to encourage competitive coding for efficiency (fastest ...
• 590
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### (Cops) Fast and Golfiest Season 1: The Lord of the Strings

Fast and Golfiest Cops Thread Welcome to the first season of Fast and Golfiest, a cops-and-robbers challenge! I designed this challenge to encourage competitive coding for efficiency (fastest ...
• 590
2k views

### Polyglot Quiz (Robbers' thread)

This is the robbers' thread. For the main rules to this challenge see the cops' thread In this challenge, robbers will choose a cop's vulnerable or safe post and try to figure out a pair of languages ...
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### Polyglot Quiz (Cops' thread)

This is the cops' thread of a cops-and-robbers challenge. The robbers' thread can be found here In this challenge as a cop you will choose two programming languages A and B, as well as a non-empty ...
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628 views

### Two In One: Guess That Language - Robbers

Cops' challenge This cops-and-robbers challenge challenges the Cop to write a non-empty program that, when run, produces some non-empty output in language A, and, when reversed, produces some non-...
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### Two In One: Guess That Language - Cops

Robber's challenge This cops-and-robbers challenge challenges the Cop to write a non-empty program that, when run, produces some non-empty output in language A, and, when reversed, produces some non-...
• 1,530
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 ...
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### Robbers: Smallest subset of characters required for Turing Completeness

This is the robbers' challenge. The cops' one is here. In Fewest (distinct) characters for Turing Completeness, the goal is to find the minimum number of characters which make a language Turing ...
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### Smallest subset of characters required for Turing Completeness

In Fewest (distinct) characters for Turing Completeness, the goal is to find the minimum number of characters which make a language Turing Complete...in other words, allow it to do any computation ...
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### What's the Missing Code? (Robbers)

Robbers' Challenge Read the cops' challenge first. In this cops-and-robbers challenge, you (the robbers) must find the correct string of characters, which, when added into the cop's code, will make it ...
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### 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
128 views

### Hello Shue! (Robbers)

Cops thread (read first) Robbers, your task is to find a Shue program p that when given the cops input i, outputs a program <...
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### Hello Shue! (Cops)

Robbers thread In this cops-and-robbers challenge, your task is to write a program h that outputs "Hello Shue!". Next, you have to choose a string ...
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821 views

### Slice the source code (Robbers)

Cops thread Robbers Robbers, your job is to find the slices of the corresponding cop's code. Scoring The robber with the most cracks wins. Example Take this code: ...
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1k views

### Slice the source code (Cops)

Robbers thread Cops Understanding slicing Remember, slices are zero-indexed. Take this slice: [2:]. If the string is "abcde", the result is "cde" because the slice basically means &...
• 3,443
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### Output two numbers (Robbers' thread)

This is the robbers' thread to a cops-and-robbers challenge. Click the link to find the cops' thread. In the cops' thread of this challenge, answerers will be writing programs which output two ...
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### Output two numbers (Cops' thread)

This is the cops' thread to a cops-and-robbers challenge. Click the link to find the robbers' thread. The challenge here is very simple. Create two programs of the same size, in the same language, ...
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449 views

### Inject arbitrary code into a compiler (robbers)

This is the robbers' challenge. To post a cop, go here. In this challenge, cops will invent a (likely simple) programming language, and write an interpreter, transpiler, or compiler that allows you to ...
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904 views

### Inject arbitrary code into a compiler (cops)

This is the cops' challenge. To post a robber, go here. In this challenge, cops will invent a (likely simple) programming language, and write an interpreter, transpiler, or compiler that allows you to ...
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470 views

### From code to golf (Robbers' thread)

This is a cops-and-robbers challenge, the cops' thread is here You can change the word code into golf by changing a letter at a ...
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880 views

### From code to golf (Cops' thread)

This is a cops-and-robbers challenge, the robbers' thread is here You can change the word code into golf by changing a letter at ...
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355 views

### Find my other token (Robbers)

Cops thread Robbers, Write a program in the cop's language using the cop's P string and your own S string, and the amount of each of them specified in the cop's post. Your S string may not exceed the ...
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856 views

### Find my other token (Cops)

Robbers thread Cops, Choose two strings of code, one public and one secret. We will call them P and S. You will be writing a program using only repetitions of these strings. For example: if you choose ...
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### Which character to change (Robbers)

Cops thread Robbers, your task is to crack a cops answer. Reveal the character that should be changed and what it should be changed to too. Please notify the cop if you cracked their challenge. The ...
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### Which character to change (Cops)

Robbers Thread Cops, your task is to chose a program that prints a string (you can choose). Although, if you change 1 character in your code, it should print another string. But there's a twist: You ...
• 8,463
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### It almost works (Robbers' Thread)

Cops' Thread Your challenge is to find an uncracked, unsafe cop on the cops thread, and find an input value for which their code does not do as specified by the challenge. You must use values within ...
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### It almost works (Cops' Thread)

Robbers' Thread Your challenge is to find an existing challenge, and implement it in a way such that certain inputs fail. At least one input must not produce the correct output (use the other ...
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417 views

### Hide a message in an image - Robbers

Choose a challenge from the Cops thread, determine the third hidden message, and describe how the system works. Keep in mind limitations and possibilities available to Cops: You are not expected to ...
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886 views

### Hide a message in an image - Cops

Robbers thread Your task is to create a method for hiding information in an image. You will post three encoded messages of your choice (keep them classy), each with its associated image. Reveal the ...
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376 views

### I'm Jelly of Python (Robbers)

What does "jelly" mean in the title?. Cop's thread Robbers, you are to choose an uncracked Cop answer, and attempt to find a Jelly program which is: shorter than the Cop's answer solves the ...
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### I'm Jelly of Python (Cops)

What does "jelly" mean in the title?. Robber's thread Jelly has an "Evaluate the argument as Python 3" atom, ŒV which takes a string as an ...
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612 views

### The Math is Right, But the Answer is Wrong - Robbers

Challenge The cops created code challenges which result in certain wildly incorrect answers despite correct math. Choose an uncracked, not safe formula from the cop thread. Your task is to find an ...
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891 views

### The Math is Right, But the Answer is Wrong - Cops

Robber Thread here The Challenge Choose any numeric* formula, algorithm, or code challenge. Implement it in such a way that the math is correct, but at least one answer is wildly** wrong due to some ...
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### Almost Illegal Strings, Mark II (Robbers)

This is the robbers' thread for 'Almost Illegal Strings'. See the cop's thread for information on participating. A section from the post is included here for convenience. The Robbers' Challenge Find ...
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### Almost Illegal Strings, Mark II (Cops)

Edit 2020-11-06: This challenge has been edited with new provisions to encourage participation. The edits have been bolded for emphasis. Welcome to a cops and robbers version of Find an Illegal ...
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6k views

Inspired by this challenge, which got closed. This is meant to be an easier, but no less interesting version of that. This is the robbers thread of a cops-and-robbers challenge. For the cops thread, ...
• 287
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Inspired by this challenge, which got closed. This is meant to be an easier, but no less interesting version of that. This is the cops thread of a cops-and-robbers challenge. For the robbers thread, ...
• 287
1k views

### Peel away the layers - Robbers

This is the Robbers thread. For the Cops challenge, see here As the robbers, your job is to crack the cops' answers. Choose an uncracked, unsafe cop answer and attempt to figure out which languages, ...
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### Peel away the layers - Cops

In this cops-and-robbers challenge, robbers must crack cop answers by finding out which languages the cops used. This is the Cops thread. For the Robbers' challenge, see here Cops, you are to write a ...
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128 views

### Robbers: There's a fault in my vault! [closed]

This is the robbers' thread. The cops' thread is located here. Robber rules Should work for all keys and secrets Should require the same number or fewer guesses as the cop's fault, to prevent brute ...
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### Cops: There's a fault in my vault! [closed]

In this game of cops and robbers, each cop will make a vault: a program that stores a secret, and requires a key to unlock. The robbers should find a way to get the vault to reveal its secret without ...
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12k views

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

This is the robber's thread of a cops-and-robbers challenge. You can view the cop's thread here A pretty common beginner style question is to print some string, but, there's a catch!, you need to do ...
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13k views

### 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 ...
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791 views

### Find the hardest OEIS sequence to golf!

Notice: This question originally had people write comments with a shorter program, rather than new answers. This has been changed so that people with shorter programs can get reputation too. Hopefully ...
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### Robbers: The Hidden OEIS Substring

This is a Cops and Robbers challenge. This is the robber's thread. The cop's thread is here. The cops will pick any sequence from the OEIS, and write a program p that prints the first integer from ...
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