Add rotational-cipher exercise (#147)

config.json

@@ -585,6 +585,17 @@
         ],
         "difficulty": 2
       },
+      {
+        "slug": "rotational-cipher",
+        "name": "Rotational Cipher",
+        "uuid": "af9aa984-1a9a-479b-94dc-8e7290ffa80e",
+        "practices": [],
+        "prerequisites": [
+          "numbers",
+          "strings"
+        ],
+        "difficulty": 2
+      },
       {
         "slug": "atbash-cipher",
         "name": "Atbash Cipher",

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": [
+    "ErikSchierboom"
+  ],
+  "files": {
+    "solution": [
+      "src/rotational_cipher.cljs"
+    ],
+    "test": [
+      "test/rotational_cipher_test.cljs"
+    ],
+    "example": [
+      ".meta/src/example.cljs"
+    ]
+  },
+  "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/src/example.cljs

@@ -0,0 +1,12 @@
+; From https://exercism.org/tracks/clojure/exercises/rotational-cipher/solutions/acamargo
+
+(ns rotational-cipher
+  (:require [clojure.string :as s]))
+
+(def ^:const alphabet "abcdefghijklmnopqrstuvwxyz")
+
+(defn rotate [text key]
+  (let [shifted (take 26 (drop (mod key 26) (cycle alphabet)))
+        cipher (zipmap (str alphabet (s/upper-case alphabet))
+                       (concat shifted (map s/upper-case shifted)))]
+    (s/join (map #(cipher %1 %1) text))))

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

@@ -0,0 +1,33 @@
+# This is an auto-generated file. Regular comments will be removed when this
+# file is regenerated. Regenerating will not touch any manually added keys,
+# so comments can be added in 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/deps.edn

@@ -0,0 +1,10 @@
+{:deps
+ {org.clojure/clojure {:mvn/version "1.10.1"}
+  org.clojure/clojurescript {:mvn/version "1.10.773"}}
+
+ :aliases
+ {:test
+  {:extra-paths ["test"]
+   :extra-deps
+   {olical/cljs-test-runner {:mvn/version "3.8.0"}}
+   :main-opts ["-m" "cljs-test-runner.main"]}}}

exercises/practice/rotational-cipher/src/rotational_cipher.cljs

@@ -0,0 +1,5 @@
+(ns rotational-cipher)
+
+(defn rotate [] ;; <- arglist goes here
+      ;; your code goes here
+)

exercises/practice/rotational-cipher/test/rotational_cipher_test.cljs

@@ -0,0 +1,46 @@
+(ns rotational-cipher-test
+  (:require  [clojure.test :refer [deftest is testing]]
+             rotational-cipher))
+
+(deftest rotate-a-by-1
+  (is (= (rotational-cipher/rotate "a" 1) "b")))
+
+(deftest rotate-a-by-26-same-output
+  (is (= (rotational-cipher/rotate "a" 26) "a")))
+
+(deftest rotate-a-by-0-same-output
+  (is (= (rotational-cipher/rotate "a" 0) "a")))
+
+(deftest rotate-m-by-13
+  (is (= (rotational-cipher/rotate "m" 13) "z")))
+
+(deftest rotate-n-by-13-with-wrap
+  (is (= (rotational-cipher/rotate "n" 13) "a")))
+
+(deftest rotate-capital-letters
+  (is (= (rotational-cipher/rotate "OMG" 5) "TRL")))
+
+(deftest rotate-spaces
+  (is (= (rotational-cipher/rotate "O M G" 5) "T R L")))
+
+(deftest rotate-numbers
+  (is (= (rotational-cipher/rotate "Testing 1 2 3 testing" 4) "Xiwxmrk 1 2 3 xiwxmrk")))
+
+(deftest rotate-punctuation
+  (is (= (rotational-cipher/rotate "Let's eat, Grandma!" 21) "Gzo'n zvo, Bmviyhv!")))
+
+(deftest rotate-opposite-direction
+  (is (= (rotational-cipher/rotate "b" -1) "a")))
+
+(deftest rotate-opposite-past-first-letter
+  (is (= (rotational-cipher/rotate "B" -2) "Z")))
+
+(deftest rotate-opposite-past-letter-count
+  (is (= (rotational-cipher/rotate "B" -28) "Z")))
+
+(deftest rotate-forward-then-backwards-same-number-of-steps
+  (is (=  (rotational-cipher/rotate
+           (rotational-cipher/rotate "B" 28) -28) "B")))
+
+(deftest rotate-all-letters
+  (is (= (rotational-cipher/rotate "The quick brown fox jumps over the lazy dog." 13) "Gur dhvpx oebja sbk whzcf bire gur ynml qbt.")))