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Challenge 12: Message Decoder

curriculum/challenges/english/blocks/daily-coding-challenges-python/68216ef80f957572e7c340c5.md

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--description--

Given a secret message string, and an integer representing the number of letters that were used to shift the message to encode it, return the decoded string.

  • A positive number means the message was shifted forward in the alphabet.
  • A negative number means the message was shifted backward in the alphabet.
  • Case matters, decoded characters should retain the case of their encoded counterparts.
  • Non-alphabetical characters should not get decoded.

--hints--

decode("Xlmw mw e wigvix qiwweki.", 4) should return "This is a secret message."

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(decode("Xlmw mw e wigvix qiwweki.", 4), "This is a secret message.")`)
}})

decode("Byffi Qilfx!", 20) should return "Hello World!"

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(decode("Byffi Qilfx!", 20), "Hello World!")`)
}})

decode("Zqd xnt njzx?", -1) should return "Are you okay?"

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(decode("Zqd xnt njzx?", -1), "Are you okay?")`)
}})

decode("oannLxmnLjvy", 9) should return "freeCodeCamp"

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertEqual(decode("oannLxmnLjvy", 9), "freeCodeCamp")`)
}})

--seed--

--seed-contents--

py
def decode(message, shift):

    return message

--solutions--

py
def decode(message, shift):
    decoded_message = []
    for char in message:
        if char.isalpha():
            base = ord('a') if char.islower() else ord('A')
            new_char = chr((ord(char) - base - shift) % 26 + base)
            decoded_message.append(new_char)
        else:
            decoded_message.append(char)
    return ''.join(decoded_message)