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Add practice exercise: atbash-cipher (#106)
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‎config.json

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

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

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

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

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{
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"authors": [
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"jimmytty"
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],
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"files": {
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"solution": [
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"atbash-cipher.sql"
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],
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"test": [
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"atbash-cipher_test.sql"
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],
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"example": [
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".meta/example.sql"
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]
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},
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"blurb": "Create an implementation of the Atbash cipher, an ancient encryption system created in the Middle East.",
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"source": "Wikipedia",
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"source_url": "https://en.wikipedia.org/wiki/Atbash"
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}

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

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

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

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# This is an auto-generated file.
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#
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# Regenerating this file via `configlet sync` will:
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# - Recreate every `description` key/value pair
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# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
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# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
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# - Preserve any other key/value pair
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#
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# As user-added comments (using the # character) will be removed when this file
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# is regenerated, comments can be added via a `comment` key.
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[2f47ebe1-eab9-4d6b-b3c6-627562a31c77]
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description = "encode -> encode yes"
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[b4ffe781-ea81-4b74-b268-cc58ba21c739]
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description = "encode -> encode no"
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[10e48927-24ab-4c4d-9d3f-3067724ace00]
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description = "encode -> encode OMG"
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[d59b8bc3-509a-4a9a-834c-6f501b98750b]
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description = "encode -> encode spaces"
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[31d44b11-81b7-4a94-8b43-4af6a2449429]
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description = "encode -> encode mindblowingly"
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[d503361a-1433-48c0-aae0-d41b5baa33ff]
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description = "encode -> encode numbers"
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[79c8a2d5-0772-42d4-b41b-531d0b5da926]
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description = "encode -> encode deep thought"
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[9ca13d23-d32a-4967-a1fd-6100b8742bab]
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description = "encode -> encode all the letters"
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[bb50e087-7fdf-48e7-9223-284fe7e69851]
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description = "decode -> decode exercism"
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[ac021097-cd5d-4717-8907-b0814b9e292c]
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description = "decode -> decode a sentence"
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[18729de3-de74-49b8-b68c-025eaf77f851]
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description = "decode -> decode numbers"
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[0f30325f-f53b-415d-ad3e-a7a4f63de034]
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description = "decode -> decode all the letters"
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[39640287-30c6-4c8c-9bac-9d613d1a5674]
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description = "decode -> decode with too many spaces"
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[b34edf13-34c0-49b5-aa21-0768928000d5]
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description = "decode -> decode with no spaces"

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

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

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

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

‎exercises/practice/atbash-cipher/create_fixture.sql

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

‎exercises/practice/atbash-cipher/create_test_table.sql

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

‎exercises/practice/atbash-cipher/data.csv

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

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