Add rotational-cipher (#257)

config.json

@@ -306,6 +306,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "rotational-cipher",
+        "name": "Rotational Cipher",
+        "uuid": "40ccdfb1-492f-4bba-917f-c40c75573ebf",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "scrabble-score",
         "name": "Scrabble Score",

exercises/practice/rotational-cipher/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+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:
+
+```text
+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.`

exercises/practice/rotational-cipher/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "src/rotational-cipher.lfe"
+    ],
+    "test": [
+      "test/rotational-cipher-tests.lfe"
+    ],
+    "example": [
+      ".meta/example.lfe"
+    ]
+  },
+  "blurb": "Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Caesar_cipher"
+}

exercises/practice/rotational-cipher/.meta/example.lfe

@@ -0,0 +1,24 @@
+(defmodule rotational-cipher
+  (export (rotate 2)))
+
+(defun rotate (text shift)
+  (do-rotate text shift ""))
+
+(defun do-rotate
+  (('() _ acc)
+   (unicode:characters_to_list (lists:reverse acc)))
+  (((cons head tail) shift acc)
+    (let ((chr (rotate-char head shift)))
+      (do-rotate tail shift (cons chr acc)))))
+
+(defun rotate-char (chr shift)
+  (cond ((and (>= chr #\A) (=< chr #\Z))
+          (let* ((relative-offset (+ (- chr #\A) shift))
+                 (codepoint (+ (rem relative-offset 26) #\A)))
+            codepoint))
+        ((and (>= chr #\a) (=< chr #\z))
+          (let* ((relative-offset (+ (- chr #\a) shift))
+                 (codepoint (+ (rem relative-offset 26) #\a)))
+            codepoint))
+        (else chr)))
+

exercises/practice/rotational-cipher/.meta/tests.toml

@@ -0,0 +1,40 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[74e58a38-e484-43f1-9466-877a7515e10f]
+description = "rotate a by 0, same output as input"
+
+[7ee352c6-e6b0-4930-b903-d09943ecb8f5]
+description = "rotate a by 1"
+
+[edf0a733-4231-4594-a5ee-46a4009ad764]
+description = "rotate a by 26, same output as input"
+
+[e3e82cb9-2a5b-403f-9931-e43213879300]
+description = "rotate m by 13"
+
+[19f9eb78-e2ad-4da4-8fe3-9291d47c1709]
+description = "rotate n by 13 with wrap around alphabet"
+
+[a116aef4-225b-4da9-884f-e8023ca6408a]
+description = "rotate capital letters"
+
+[71b541bb-819c-4dc6-a9c3-132ef9bb737b]
+description = "rotate spaces"
+
+[ef32601d-e9ef-4b29-b2b5-8971392282e6]
+description = "rotate numbers"
+
+[32dd74f6-db2b-41a6-b02c-82eb4f93e549]
+description = "rotate punctuation"
+
+[9fb93fe6-42b0-46e6-9ec1-0bf0a062d8c9]
+description = "rotate all letters"

exercises/practice/rotational-cipher/Makefile

@@ -0,0 +1,21 @@
+ERL    := $(shell which erl)
+REBAR3 := $(shell which rebar3)
+
+null  :=
+space := $(null) #
+comma := ,
+
+ifeq ($(ERL),)
+  $(error Can't find Erlang executable 'erl')
+else ifeq ($(REBAR3),)
+  $(error Can't find rebar3)
+endif
+
+compile: ; $(REBAR3) compile
+
+clean: ; $(REBAR3) clean
+
+.PHONY: test
+test:
+	$(REBAR3) eunit \
+	-m $(subst $(space),$(comma),$(basename $(notdir $(wildcard test/*.lfe))))

exercises/practice/rotational-cipher/rebar.config

@@ -0,0 +1,11 @@
+{plugins, [{rebar3_lfe, "0.4.10"}]}.
+
+{provider_hooks, [{post, [{compile, {lfe, compile}}]}]}.
+
+{deps, [{lfe, "2.1.3"}]}.
+
+{profiles,
+ [{test,
+   [{eunit_compile_opts, [{src_dirs, ["src", "test"]}]},
+    {deps,
+     [{ltest, "0.13.8"}]}]}]}.

exercises/practice/rotational-cipher/rebar.lock

@@ -0,0 +1,8 @@
+{"1.2.0",
+[{<<"lfe">>,{pkg,<<"lfe">>,<<"2.1.3">>},0}]}.
+[
+{pkg_hash,[
+ {<<"lfe">>, <<"6EFCB2BBC1FFC21DC5D1C092F00EFDB397EAC889474AC5C86EDF78A3557CC730">>}]},
+{pkg_hash_ext,[
+ {<<"lfe">>, <<"4E4BAD515A169AE418FEB7374EA1C8D741FAEA9D95E266CE343B45BCC377F55B">>}]}
+].

exercises/practice/rotational-cipher/src/rotational-cipher.app.src

@@ -0,0 +1,11 @@
+%% -*- erlang -*-
+{application, 'rotational-cipher',
+ [{description, "exercism.org exercise: Rotational Cipher"},
+  {vsn, "0.0.1"},
+  {modules,
+   ['rotational-cipher']},
+  {registered, []},
+  {applications,
+   [kernel, stdlib]},
+  {included_applications, []},
+  {env, []}]}.

exercises/practice/rotational-cipher/src/rotational-cipher.lfe

@@ -0,0 +1,5 @@
+(defmodule rotational-cipher
+  (export (rotate 2)))
+
+  ; Please implement the rotate function.
+

exercises/practice/rotational-cipher/test/rotational-cipher-tests.lfe

@@ -0,0 +1,47 @@
+(defmodule rotational-cipher-tests
+  (behaviour ltest-unit)
+  (export all))
+
+(include-lib "ltest/include/ltest-macros.lfe")
+
+(deftest rotate-a-by-0-same-output-as-input
+  (is-equal "a"
+            (rotational-cipher:rotate "a" 0)))
+
+(deftest rotate-a-by-1
+  (is-equal "b"
+            (rotational-cipher:rotate "a" 1)))
+
+(deftest rotate-a-by-26-same-output-as-input
+  (is-equal "a"
+            (rotational-cipher:rotate "a" 26)))
+
+(deftest rotate-m-by-13
+  (is-equal "z"
+            (rotational-cipher:rotate "m" 13)))
+
+(deftest rotate-n-by-13-with-wrap-around-alphabet
+  (is-equal "a"
+            (rotational-cipher:rotate "n" 13)))
+
+(deftest rotate-capital-letters
+  (is-equal "TRL"
+            (rotational-cipher:rotate "OMG" 5)))
+
+(deftest rotate-spaces
+  (is-equal "T R L"
+            (rotational-cipher:rotate "O M G" 5)))
+
+(deftest rotate-numbers
+  (is-equal "Xiwxmrk 1 2 3 xiwxmrk"
+            (rotational-cipher:rotate "Testing 1 2 3 testing" 4)))
+
+(deftest rotate-punctuation
+  (is-equal "Gzo'n zvo, Bmviyhv!"
+            (rotational-cipher:rotate "Let's eat, Grandma!" 21)))
+
+(deftest rotate-all-letters
+  (is-equal "Gur dhvpx oebja sbk whzcf bire gur ynml qbt."
+            (rotational-cipher:rotate "The quick brown fox jumps over the lazy dog."
+                                      13)))
+