Rotational Cipher

Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.

The Caesar cipher is a simple shift cipher that relies on transposing all the letters in the alphabet using an integer key between 0 and 26. Using a key of 0 or 26 will always yield the same output due to modular arithmetic. The letter is shifted for as many values as the value of the key.

The general notation for rotational ciphers is ROT + <key>. The most commonly used rotational cipher is ROT13.

A ROT13 on the Latin alphabet would be as follows:

Plain:  abcdefghijklmnopqrstuvwxyz
Cipher: nopqrstuvwxyzabcdefghijklm

It is stronger than the Atbash cipher because it has 27 possible keys, and 25 usable keys.

Ciphertext is written out in the same formatting as the input including spaces and punctuation.

Examples

ROT5 omg gives trl
ROT0 c gives c
ROT26 Cool gives Cool
ROT13 The quick brown fox jumps over the lazy dog. gives Gur dhvpx oebja sbk whzcf bire gur ynml qbt.
ROT13 Gur dhvpx oebja sbk whzcf bire gur ynml qbt. gives The quick brown fox jumps over the lazy dog.

This is a good exercise to experiment with non-standard string literals and metaprogramming.

A short introduction to non-standard string literals can be found in this blog post. A detailed metaprogramming guide can be found in the manual.

You can extend your solution by adding the functionality described below. To test your solution, you have to remove the comments at the end of runtests.jl before running the tests as usual.

Bonus A only requires basics as outlined in the blog post. Bonus B requires significantly more knowledge of metaprogramming in Julia.

Bonus A

Implement a string literal that acts as ROT13 on the string:

R13"abcdefghijklmnopqrstuvwxyz" == "nopqrstuvwxyzabcdefghijklm"

Bonus B

Implement string literals R<i>, i = 0, ..., 26, that shift the string for i values:

R0"Hello, World!" == "Hello, World!"
R4"Testing 1 2 3 testing" == "Xiwxmrk 1 2 3 xiwxmrk"
R13"abcdefghijklmnopqrstuvwxyz" == "nopqrstuvwxyzabcdefghijklm"

Source

Wikipedia https://en.wikipedia.org/wiki/Caesar_cipher

Version compatibility

This exercise has been tested on Julia versions >=1.0.

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

Your solution



In [ ]:

    
# submit

Test suite



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using Test

# include("rotational-cipher.jl")

@testset "rotate function" begin
    @testset "rotate by n" begin
        @testset "no wrap" begin
            @test rotate(1, "a") == "b"
            @test rotate(1, 'a') == 'b'
            @test rotate(13, "m") == "z"
            @test rotate(13, 'm') == 'z'
        end
        @testset "wrap around" begin
            @test rotate(13, "n") == "a"
            @test rotate(13, 'n') == 'a'
        end
    end

    @testset "full rotation" begin
        @test rotate(26, "a") == "a"
        @test rotate(26, 'a') == 'a'
        @test rotate(0, "a") == "a"
        @test rotate(0, 'a') == 'a'
    end

    @testset "full strings" begin
        @test rotate(5, "OMG") == "TRL"
        @test rotate(5, "O M G") == "T R L"
        @test rotate(4, "Testing 1 2 3 testing") == "Xiwxmrk 1 2 3 xiwxmrk"
        @test rotate(21, "Let's eat, Grandma!") == "Gzo'n zvo, Bmviyhv!"
        @test rotate(13, "The quick brown fox jumps over the lazy dog.") == "Gur dhvpx oebja sbk whzcf bire gur ynml qbt."
    end
end

# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
# Additional exercises                                                        #
# Change @test_skip to @test for the optional bonus exercises from HINTS.md   #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #

# Bonus A
@testset "Bonus A: string literal R13" begin
    @test_skip R13"The quick brown fox jumps over the lazy dog." == "Gur dhvpx oebja sbk whzcf bire gur ynml qbt."
end

# Bonus B
@testset "Bonus B: string literals" begin
    @test_skip R5"OMG" == "TRL"
    @test_skip R4"Testing 1 2 3 testing" == "Xiwxmrk 1 2 3 xiwxmrk"
    @test_skip R21"Let's eat, Grandma!" == "Gzo'n zvo, Bmviyhv!"
    @test_skip R13"The quick brown fox jumps over the lazy dog." == "Gur dhvpx oebja sbk whzcf bire gur ynml qbt."
end

Prepare submission

To submit your exercise, you need to save your solution in a file called rotational-cipher.jl before using the CLI. You can either create it manually or use the following functions, which will automatically write every notebook cell that starts with # submit to the file rotational-cipher.jl.



In [ ]:

    
# using Pkg; Pkg.add("Exercism")
# using Exercism
# Exercism.create_submission("rotational-cipher")