* add practice exercise: atbash-cipher

config.json

@@ -218,6 +218,14 @@
         "prerequisites": [],
         "difficulty": 8
       },
+      {
+        "slug": "atbash-cipher",
+        "name": "Atbash Cipher",
+        "uuid": "171c0743-9e22-4152-af26-831ca097ea04",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 8
+      },
       {
         "slug": "collatz-conjecture",
         "name": "Collatz Conjecture",

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": [
+    "jimmytty"
+  ],
+  "files": {
+    "solution": [
+      "atbash-cipher.sql"
+    ],
+    "test": [
+      "atbash-cipher_test.sql"
+    ],
+    "example": [
+      ".meta/example.sql"
+    ]
+  },
+  "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/example.sql

@@ -0,0 +1,57 @@
+UPDATE "atbash-cipher"
+   SET result = (
+     WITH RECURSIVE rcte (i, c, string) AS (
+       VALUES(1, NULL, (
+         WITH RECURSIVE encode (phrase, c) AS (
+           VALUES(LOWER(phrase), NULL)
+           UNION ALL
+           SELECT SUBSTR(phrase, 2), SUBSTR(phrase, 1, 1)
+           FROM encode
+           WHERE phrase <> ''
+         )
+         SELECT GROUP_CONCAT(c, '') AS result
+           FROM (
+             SELECT CASE
+                    WHEN (UNICODE(c) BETWEEN UNICODE('a') AND UNICODE('z'))
+                      THEN CHAR(UNICODE('z') - (UNICODE(c) - UNICODE('a')))
+                    WHEN (UNICODE(c) BETWEEN UNICODE('0') AND UNICODE('9'))
+                      THEN c
+                    END AS c
+               FROM encode
+           )
+          WHERE c NOT NULL
+       ))
+       UNION ALL
+       SELECT i + 1,
+       SUBSTR(string, 1, 1) || IIF(i % 5 = 0, ' ', ''),
+       SUBSTR(string, 2)
+       FROM rcte
+       WHERE string <> ''
+     )
+     SELECT TRIM(GROUP_CONCAT(c, '')) FROM rcte
+   )
+ WHERE property = 'encode'
+       ;
+
+UPDATE "atbash-cipher"
+   SET result = (
+     WITH RECURSIVE decode (phrase, c) AS (
+       VALUES(phrase, NULL)
+       UNION ALL
+       SELECT SUBSTR(phrase, 2), SUBSTR(phrase, 1, 1)
+       FROM decode
+       WHERE phrase <> ''
+     )
+     SELECT GROUP_CONCAT(c, '') AS result
+       FROM (
+         SELECT CASE
+                WHEN (UNICODE(c) BETWEEN UNICODE('a') AND UNICODE('z'))
+                  THEN CHAR(UNICODE('z') - UNICODE(c) + UNICODE('a'))
+                WHEN (UNICODE(c) BETWEEN UNICODE('0') AND UNICODE('9')) THEN c
+                END AS c
+           FROM decode
+       )
+      WHERE c NOT NULL
+   )
+ WHERE property = 'decode'
+       ;

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

@@ -0,0 +1,52 @@
+# 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.
+
+[2f47ebe1-eab9-4d6b-b3c6-627562a31c77]
+description = "encode -> encode yes"
+
+[b4ffe781-ea81-4b74-b268-cc58ba21c739]
+description = "encode -> encode no"
+
+[10e48927-24ab-4c4d-9d3f-3067724ace00]
+description = "encode -> encode OMG"
+
+[d59b8bc3-509a-4a9a-834c-6f501b98750b]
+description = "encode -> encode spaces"
+
+[31d44b11-81b7-4a94-8b43-4af6a2449429]
+description = "encode -> encode mindblowingly"
+
+[d503361a-1433-48c0-aae0-d41b5baa33ff]
+description = "encode -> encode numbers"
+
+[79c8a2d5-0772-42d4-b41b-531d0b5da926]
+description = "encode -> encode deep thought"
+
+[9ca13d23-d32a-4967-a1fd-6100b8742bab]
+description = "encode -> encode all the letters"
+
+[bb50e087-7fdf-48e7-9223-284fe7e69851]
+description = "decode -> decode exercism"
+
+[ac021097-cd5d-4717-8907-b0814b9e292c]
+description = "decode -> decode a sentence"
+
+[18729de3-de74-49b8-b68c-025eaf77f851]
+description = "decode -> decode numbers"
+
+[0f30325f-f53b-415d-ad3e-a7a4f63de034]
+description = "decode -> decode all the letters"
+
+[39640287-30c6-4c8c-9bac-9d613d1a5674]
+description = "decode -> decode with too many spaces"
+
+[b34edf13-34c0-49b5-aa21-0768928000d5]
+description = "decode -> decode with no spaces"

exercises/practice/atbash-cipher/atbash-cipher.sql

@@ -0,0 +1,7 @@
+-- Schema: CREATE TABLE "atbash-cipher" (
+--           property TEXT NOT NULL,
+--           phrase   TEXT NOT NULL,
+--           result   TEXT
+--         );
+-- Task: update the atbash-cipher table and set the result based on
+--       property and phrase

exercises/practice/atbash-cipher/atbash-cipher_test.sql

@@ -0,0 +1,43 @@
+-- Create database:
+.read ./create_fixture.sql
+
+-- Read user student solution and save any output as markdown in user_output.md:
+.mode markdown
+.output user_output.md
+.read ./atbash-cipher.sql
+.output
+
+-- Create a clean testing environment:
+.read ./create_test_table.sql
+
+-- Comparison of user input and the tests updates the status for each test:
+UPDATE tests
+SET status = 'pass'
+FROM (SELECT property, phrase, result FROM "atbash-cipher") AS actual
+WHERE (actual.property, actual.phrase, actual.result) = (tests.property, tests.phrase, tests.expected);
+
+-- Update message for failed tests to give helpful information:
+UPDATE tests
+SET message = (
+    'Result for "'
+    || JSON_OBJECT(
+         'property', tests.property,
+         'phrase',   tests.phrase
+       )
+    || '"'
+    || ' is <' || COALESCE(actual.result, 'NULL')
+    || '> but should be <' || tests.expected || '>'
+)
+FROM (SELECT property, phrase, result FROM "atbash-cipher") AS actual
+WHERE (actual.property, actual.phrase) = (tests.property, tests.phrase) AND tests.status = 'fail';
+
+-- Save results to ./output.json (needed by the online test-runner)
+.mode json
+.once './output.json'
+SELECT description, status, message, output, test_code, task_id
+FROM tests;
+
+-- Display test results in readable form for the student:
+.mode table
+SELECT description, status, message
+FROM tests;

exercises/practice/atbash-cipher/create_fixture.sql

@@ -0,0 +1,9 @@
+DROP TABLE IF EXISTS "atbash-cipher";
+CREATE TABLE "atbash-cipher" (
+  property TEXT NOT NULL,
+  phrase   TEXT NOT NULL,
+  result   TEXT
+);
+
+.mode csv
+.import ./data.csv "atbash-cipher"

exercises/practice/atbash-cipher/create_test_table.sql

@@ -0,0 +1,33 @@
+DROP TABLE IF EXISTS tests;
+CREATE TABLE IF NOT EXISTS tests (
+    -- uuid and description are taken from the test.toml file
+    uuid TEXT PRIMARY KEY,
+    description TEXT NOT NULL,
+    -- The following section is needed by the online test-runner
+    status TEXT DEFAULT 'fail',
+    message TEXT,
+    output TEXT,
+    test_code TEXT,
+    task_id INTEGER DEFAULT NULL,
+    -- Here are columns for the actual tests
+    property TEXT NOT NULL,
+    phrase   TEXT NOT NULL,
+    expected TEXT NOT NULL
+);
+
+INSERT INTO tests (uuid, description, property, phrase, expected)
+    VALUES
+        ('2f47ebe1-eab9-4d6b-b3c6-627562a31c77','encode yes','encode','yes','bvh'),
+        ('b4ffe781-ea81-4b74-b268-cc58ba21c739','encode no','encode','no','ml'),
+        ('10e48927-24ab-4c4d-9d3f-3067724ace00','encode OMG','encode','OMG','lnt'),
+        ('d59b8bc3-509a-4a9a-834c-6f501b98750b','encode spaces','encode','O M G','lnt'),
+        ('31d44b11-81b7-4a94-8b43-4af6a2449429','encode mindblowingly','encode','mindblowingly','nrmwy oldrm tob'),
+        ('d503361a-1433-48c0-aae0-d41b5baa33ff','encode numbers','encode','Testing,1 2 3, testing.','gvhgr mt123 gvhgr mt'),
+        ('79c8a2d5-0772-42d4-b41b-531d0b5da926','encode deep thought','encode','Truth is fiction.','gifgs rhurx grlm'),
+        ('9ca13d23-d32a-4967-a1fd-6100b8742bab','encode all the letters','encode','The quick brown fox jumps over the lazy dog.','gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt'),
+        ('bb50e087-7fdf-48e7-9223-284fe7e69851','decode exercism','decode','vcvix rhn','exercism'),
+        ('ac021097-cd5d-4717-8907-b0814b9e292c','decode a sentence','decode','zmlyh gzxov rhlug vmzhg vkkrm thglm v','anobstacleisoftenasteppingstone'),
+        ('18729de3-de74-49b8-b68c-025eaf77f851','decode numbers','decode','gvhgr mt123 gvhgr mt','testing123testing'),
+        ('0f30325f-f53b-415d-ad3e-a7a4f63de034','decode all the letters','decode','gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt','thequickbrownfoxjumpsoverthelazydog'),
+        ('39640287-30c6-4c8c-9bac-9d613d1a5674','decode with too many spaces','decode','vc vix    r hn','exercism'),
+        ('b34edf13-34c0-49b5-aa21-0768928000d5','decode with no spaces','decode','zmlyhgzxovrhlugvmzhgvkkrmthglmv','anobstacleisoftenasteppingstone');

exercises/practice/atbash-cipher/data.csv

@@ -0,0 +1,14 @@
+"encode","yes",""
+"encode","no",""
+"encode","OMG",""
+"encode","O M G",""
+"encode","mindblowingly",""
+"encode","Testing,1 2 3, testing.",""
+"encode","Truth is fiction.",""
+"encode","The quick brown fox jumps over the lazy dog.",""
+"decode","vcvix rhn",""
+"decode","zmlyh gzxov rhlug vmzhg vkkrm thglm v",""
+"decode","gvhgr mt123 gvhgr mt",""
+"decode","gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt",""
+"decode","vc vix    r hn",""
+"decode","zmlyhgzxovrhlugvmzhgvkkrmthglmv",""