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Challenges

Comments on Beaver Code Decryption

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Beaver Code Decryption

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Credit

This challenge is taken with permission from https://www.mysterytwisterc3.org/en/challenges/level-1/beaver-code

Description

The encryption method is as follows:

The plaintext is divided into two halves, odd positions and even positions.

Example: 'CRYPTO' -> ['CYT','RPO']

This is then applied recursively to both halves, until each part is two letters or less. The parts are then merged.

'CRYPTO' -> ['CYT','RPO'] -> [['CT','Y'], ['RO','P']] -> 'CTYROP'

Challenge

Given a string encrypted with this method, decrypt it.

Valid input formats: ['CTYROP'], 'CTYROP'

Test cases

CTYROP -> CRYPTO
EOYCTNNPRI -> ENCRYPTION
RUOENFSEAFMRDHT -> RANDOMSTUFFHERE

Note: the encryption of the last test case is the same as the decryption, make sure you're decrypting!

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General comments (1 comment)
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Solutions by ngn

https://chat.stackexchange.com/transcript/message/57690032#57690032

APL 17: {⍵[⍋⍋⍉⊖2⊥⍣¯1⍳≢⍵]}

ngn/k 13: {x@<<+|2\!#x}

These are too good not to post.

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General comments (3 comments)
General comments
user‭ wrote over 3 years ago

These look awesome. Do you have explanations?

Razetime‭ wrote over 3 years ago

The chat says it assumes input length is under some limit?

rak1507‭ wrote over 3 years ago

These don't assume that. The explanation is based on the fact this is a bit reversal permutation https://en.wikipedia.org/wiki/Bit-reversal_permutation