73 lines
2.1 KiB
Markdown
73 lines
2.1 KiB
Markdown
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# Rotational Cipher
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Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.
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The Caesar cipher is a simple shift cipher that relies on
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transposing all the letters in the alphabet using an integer key
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between `0` and `26`. Using a key of `0` or `26` will always yield
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the same output due to modular arithmetic. The letter is shifted
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for as many values as the value of the key.
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The general notation for rotational ciphers is `ROT + <key>`.
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The most commonly used rotational cipher is `ROT13`.
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A `ROT13` on the Latin alphabet would be as follows:
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```text
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Plain: abcdefghijklmnopqrstuvwxyz
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Cipher: nopqrstuvwxyzabcdefghijklm
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```
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It is stronger than the Atbash cipher because it has 27 possible keys, and 25 usable keys.
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Ciphertext is written out in the same formatting as the input including spaces and punctuation.
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## Examples
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- ROT5 `omg` gives `trl`
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- ROT0 `c` gives `c`
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- ROT26 `Cool` gives `Cool`
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- ROT13 `The quick brown fox jumps over the lazy dog.` gives `Gur dhvpx oebja sbk whzcf bire gur ynml qbt.`
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- ROT13 `Gur dhvpx oebja sbk whzcf bire gur ynml qbt.` gives `The quick brown fox jumps over the lazy dog.`
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## Running tests
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Execute the tests with:
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```bash
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$ elixir rotational_cipher_test.exs
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```
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### Pending tests
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In the test suites, all but the first test have been skipped.
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Once you get a test passing, you can unskip the next one by
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commenting out the relevant `@tag :pending` with a `#` symbol.
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For example:
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```elixir
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# @tag :pending
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test "shouting" do
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assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
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end
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```
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Or, you can enable all the tests by commenting out the
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`ExUnit.configure` line in the test suite.
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```elixir
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# ExUnit.configure exclude: :pending, trace: true
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```
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For more detailed information about the Elixir track, please
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see the [help page](http://exercism.io/languages/elixir).
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## Source
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Wikipedia [https://en.wikipedia.org/wiki/Caesar_cipher](https://en.wikipedia.org/wiki/Caesar_cipher)
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## Submitting Incomplete Solutions
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It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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