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Ruby Implementation of a Rotational Cipher. Wrote in
$alphabet = 'abcdefghijklmnopqurstvwxyz'
# Get an index of an alphabetic letter based on the index and offset
def calculateOffset(index, offset)
index += offset
index -= 26 while index >= 26 # keep subtracting until we get to the right range
# Get a char from the alphabet based on an offset
def getCharByOffset(char, offset=0)
# Chars could be in the upper alphabet, the lower alphabet, or neither.
indexUpper = $ALPHABET.index(char)
indexLower = $alphabet.index(char)
if indexUpper
i = calculateOffset(indexUpper, offset)
char = $ALPHABET[i].chr # Get the char at that index
elsif indexLower
i = calculateOffset(indexLower, offset)
char = $alphabet[i].chr
# Rotationally encode a string
def rotx(x, string, encrypt=true)
newString = ''
x = -x unless encrypt
# for each char in the string
string.each_char do |char|
# TODO: support decryption
newString << getCharByOffset(char, x)
# get a new char that is `x` away in the alphabet
# ------------------------------------------------ Assertions
puts rotx 10, 'Hello, World'
# => "Rovvy, Gybvn" # Shouldn't this be "Rovvy, Gycvn"?
puts rotx 10, 'Rovvy, Gycvn', false
# => "Hello, World"
# Rotation numbers greater than 26 should work as well
puts rotx 36, 'Hello, World'
# => "Rovvy, Gybvn"
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