I must implement a simple Caesar cipher class. Initializer takes two parameters - number of positions to shift the alphabet (integer) and the alphabet used (as string, not necessarily the standard English alphabet). The class must have two instance methods encrypt and decrypt, which take a string and do the respective action based on the parameters of the initializer. These are my rspec tests:

describe "Caesar" do
 latin_encrypter = Caesar.new 4
 dna_encrypter = Caesar.new 3, 'ACTG'
 it 'encrypts correctly' do
 expect(latin_encrypter.encrypt 'hello').to eq "lipps"
 end
 it 'encrypts correctly using DNA alphabet' do
 expect(dna_encrypter.encrypt 'ACCTGA').to eq "GAACTG"
 end
 it 'decrypts correctly' do
 expect(latin_encrypter.decrypt 'lipps').to eq 'hello'
 end
 it 'decrypts correctly using DNA alphabet' do
 expect(dna_encrypter.decrypt 'GAACTG').to eq 'ACCTGA'
 end
end

and this is my implementation:

class Caesar
 def initialize(shift, alphabet = 'abcdefghijklmnopqrstuvwxyz')
 @shift = shift % alphabet.size
 @alphabet = alphabet
 end
 def encrypt(string)
 string.chars.map { |char| @alphabet[@alphabet.index(char) + @shift - @alphabet.size] }.join
 end
 def decrypt(string)
 string.chars.map { |char| @alphabet[@alphabet.index(char) - @shift] }.join
 end
end

Is this an optimal algorithm for encryption/decryption or is there a better one (perhaps using gsub)?

ruby

lang-rb