Add atbash-cipher exercise (#114)

Author: ErikSchierboom

config.json

@@ -585,6 +585,18 @@
         ],
         "difficulty": 2
       },
+      {
+        "slug": "atbash-cipher",
+        "name": "Atbash Cipher",
+        "uuid": "afb8e97c-6600-419c-a121-7cd3bcf870ee",
+        "practices": [],
+        "prerequisites": [
+          "numbers",
+          "conditionals",
+          "strings"
+        ],
+        "difficulty": 3
+      },
       {
         "slug": "minesweeper",
         "name": "Minesweeper",

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

@@ -0,0 +1,27 @@
+# Instructions
+
+Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.
+
+The Atbash cipher is a simple substitution cipher that relies on transposing all the letters in the alphabet such that the resulting alphabet is backwards.
+The first letter is replaced with the last letter, the second with the second-last, and so on.
+
+An Atbash cipher for the Latin alphabet would be as follows:
+
+```text
+Plain:  abcdefghijklmnopqrstuvwxyz
+Cipher: zyxwvutsrqponmlkjihgfedcba
+```
+
+It is a very weak cipher because it only has one possible key, and it is a simple mono-alphabetic substitution cipher.
+However, this may not have been an issue in the cipher's time.
+
+Ciphertext is written out in groups of fixed length, the traditional group size being 5 letters, leaving numbers unchanged, and punctuation is excluded.
+This is to make it harder to guess things based on word boundaries.
+All text will be encoded as lowercase letters.
+
+## Examples
+
+- Encoding `test` gives `gvhg`
+- Encoding `x123 yes` gives `c123b vh`
+- Decoding `gvhg` gives `test`
+- Decoding `gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt` gives `thequickbrownfoxjumpsoverthelazydog`

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

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ErikSchierboom"
+  ],
+  "files": {
+    "solution": [
+      "src/atbash_cipher.cljs"
+    ],
+    "test": [
+      "test/atbash_cipher_test.cljs"
+    ],
+    "example": [
+      ".meta/src/example.cljs"
+    ]
+  },
+  "blurb": "Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Atbash"
+}

exercises/practice/atbash-cipher/.meta/src/example.cljs

@@ -0,0 +1,45 @@
+; Courtesy from: https://exercism.org/tracks/clojure/exercises/atbash-cipher/solutions/joebutler2
+
+(ns atbash-cipher
+  (:require [clojure.string :as str]))
+
+(def translation
+  {
+   "a" "z"
+   "b" "y"
+   "c" "x"
+   "d" "w"
+   "e" "v"
+   "f" "u"
+   "g" "t"
+   "h" "s"
+   "i" "r"
+   "j" "q"
+   "k" "p"
+   "l" "o"
+   "m" "n"
+   "n" "m"
+   "o" "l"
+   "p" "k"
+   "q" "j"
+   "r" "i"
+   "s" "h"
+   "t" "g"
+   "u" "f"
+   "v" "e"
+   "w" "d"
+   "x" "c"
+   "y" "b"
+   "z" "a"
+})
+
+(defn encode [input]
+  (->> input
+       (str/lower-case)
+       (re-seq #"\w|\d")
+       (map #(get translation % %))
+       (partition-all 5)
+       (map #(cons %2 %) (repeat " "))
+       (flatten)
+       (str/join)
+       (str/trimr)))

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

@@ -0,0 +1,45 @@
+# 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.
+
+[2f47ebe1-eab9-4d6b-b3c6-627562a31c77]
+description = "encode yes"
+
+[b4ffe781-ea81-4b74-b268-cc58ba21c739]
+description = "encode no"
+
+[10e48927-24ab-4c4d-9d3f-3067724ace00]
+description = "encode OMG"
+
+[d59b8bc3-509a-4a9a-834c-6f501b98750b]
+description = "encode spaces"
+
+[31d44b11-81b7-4a94-8b43-4af6a2449429]
+description = "encode mindblowingly"
+
+[d503361a-1433-48c0-aae0-d41b5baa33ff]
+description = "encode numbers"
+
+[79c8a2d5-0772-42d4-b41b-531d0b5da926]
+description = "encode deep thought"
+
+[9ca13d23-d32a-4967-a1fd-6100b8742bab]
+description = "encode all the letters"
+
+[bb50e087-7fdf-48e7-9223-284fe7e69851]
+description = "decode exercism"
+
+[ac021097-cd5d-4717-8907-b0814b9e292c]
+description = "decode a sentence"
+
+[18729de3-de74-49b8-b68c-025eaf77f851]
+description = "decode numbers"
+
+[0f30325f-f53b-415d-ad3e-a7a4f63de034]
+description = "decode all the letters"
+
+[39640287-30c6-4c8c-9bac-9d613d1a5674]
+description = "decode with too many spaces"
+
+[b34edf13-34c0-49b5-aa21-0768928000d5]
+description = "decode with no spaces"

exercises/practice/atbash-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/atbash-cipher/src/atbash_cipher.cljs

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

exercises/practice/atbash-cipher/test/atbash_cipher_test.cljs

@@ -0,0 +1,30 @@
+(ns atbash-cipher-test
+  (:require [clojure.test :refer [deftest is]]
+            atbash-cipher))
+
+(deftest encode-no
+  (is (= "ml" (atbash-cipher/encode "no"))))
+
+(deftest encode-yes
+  (is (= "bvh" (atbash-cipher/encode "yes"))))
+
+(deftest encode-OMG
+  (is (= "lnt" (atbash-cipher/encode "OMG"))))
+
+(deftest encode-O-M-G
+  (is (= "lnt" (atbash-cipher/encode "O M G"))))
+
+(deftest encode-long-word
+  (is (= "nrmwy oldrm tob" (atbash-cipher/encode "mindblowingly"))))
+
+(deftest encode-numbers
+  (is (= "gvhgr mt123 gvhgr mt"
+         (atbash-cipher/encode "Testing, 1 2 3, testing."))))
+
+(deftest encode-sentence
+  (is (= "gifgs rhurx grlm" (atbash-cipher/encode "Truth is fiction."))))
+
+(deftest encode-all-the-things
+  (let [plaintext "The quick brown fox jumps over the lazy dog."
+        cipher    "gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt"]
+    (is (= cipher (atbash-cipher/encode plaintext)))))