Rosetta Code Popular

Caesar Cipher

Encode and decode text by rotating alphabetic characters through a fixed shift.

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Sourcerosettacode/popular/caesar_cipher.vibe
def rotate_index(index: int, shift: int) -> int
  rotated = index + shift

  while rotated >= 26
    rotated = rotated - 26
  end

  while rotated < 0
    rotated = rotated + 26
  end

  rotated
end

def rotate_char(char: string, shift: int) -> string
  upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
  lower = "abcdefghijklmnopqrstuvwxyz"

  upper_index = upper.index(char)
  if upper_index != nil
    return upper.chars.fetch(rotate_index(upper_index, shift))
  end

  lower_index = lower.index(char)
  if lower_index != nil
    return lower.chars.fetch(rotate_index(lower_index, shift))
  end

  char
end

def caesar_cipher(text: string, shift: int) -> string
  text_chars = text.chars
  output = ""
  index = 0

  while index < text.length
    output = output + rotate_char(text_chars.fetch(index), shift)
    index = index + 1
  end

  output
end

def run -> { decoded: string, encoded: string, plain: string }
  plain = "The quick brown fox jumps over the lazy dog."
  encoded = caesar_cipher(plain, 3)
  {
    plain: plain,
    encoded: encoded,
    decoded: caesar_cipher(encoded, 23)
  }
end

Output

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