Add practice exercise: flatten-array

config.json

@@ -194,6 +194,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "flatten-array",
+        "name": "Flatten Array",
+        "uuid": "a658e1ed-26f4-4f36-9d6c-41d6f23568f9",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "house",
         "name": "House",

exercises/practice/flatten-array/.docs/instructions.append.md

@@ -0,0 +1,7 @@
+# SQLite-specific instructions
+
+## JSON documentation
+
+[JSON Functions And Operators][json-docs]
+
+[json-docs]: https://www.sqlite.org/json1.html

exercises/practice/flatten-array/.docs/instructions.md

@@ -0,0 +1,16 @@
+# Instructions
+
+Take a nested array of any depth and return a fully flattened array.
+
+Note that some language tracks may include null-like values in the input array, and the way these values are represented varies by track.
+Such values should be excluded from the flattened array.
+
+Additionally, the input may be of a different data type and contain different types, depending on the track.
+
+Check the test suite for details.
+
+## Example
+
+input: `[1, [2, 6, null], [[null, [4]], 5]]`
+
+output: `[1, 2, 6, 4, 5]`

exercises/practice/flatten-array/.docs/introduction.md

@@ -0,0 +1,7 @@
+# Introduction
+
+A shipment of emergency supplies has arrived, but there's a problem.
+To protect from damage, the items — flashlights, first-aid kits, blankets — are packed inside boxes, and some of those boxes are nested several layers deep inside other boxes!
+
+To be prepared for an emergency, everything must be easily accessible in one box.
+Can you unpack all the supplies and place them into a single box, so they're ready when needed most?

exercises/practice/flatten-array/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "jimmytty"
+  ],
+  "files": {
+    "solution": [
+      "flatten-array.sql"
+    ],
+    "test": [
+      "flatten-array_test.sql"
+    ],
+    "example": [
+      ".meta/example.sql"
+    ]
+  },
+  "blurb": "Take a nested list and return a single list with all values except nil/null.",
+  "source": "Interview Question",
+  "source_url": "https://reference.wolfram.com/language/ref/Flatten.html"
+}

exercises/practice/flatten-array/.meta/example.sql

@@ -0,0 +1,8 @@
+UPDATE "flatten-array"
+   SET result = (
+         SELECT JSON_GROUP_ARRAY(j.value)
+           FROM JSON_TREE(JSON(array)) j
+          WHERE j.type <> 'array'
+            AND j.value NOTNULL
+       )
+;

exercises/practice/flatten-array/.meta/tests.toml

@@ -0,0 +1,63 @@
+# 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.
+
+[8c71dabd-da60-422d-a290-4a571471fb14]
+description = "empty"
+
+[d268b919-963c-442d-9f07-82b93f1b518c]
+description = "no nesting"
+
+[3f15bede-c856-479e-bb71-1684b20c6a30]
+description = "flattens a nested array"
+
+[c84440cc-bb3a-48a6-862c-94cf23f2815d]
+description = "flattens array with just integers present"
+
+[d3d99d39-6be5-44f5-a31d-6037d92ba34f]
+description = "5 level nesting"
+
+[d572bdba-c127-43ed-bdcd-6222ac83d9f7]
+description = "6 level nesting"
+
+[0705a8e5-dc86-4cec-8909-150c5e54fa9c]
+description = "null values are omitted from the final result"
+
+[c6cf26de-8ccd-4410-84bd-b9efd88fd2bc]
+description = "consecutive null values at the front of the list are omitted from the final result"
+include = false
+
+[bc72da10-5f55-4ada-baf3-50e4da02ec8e]
+description = "consecutive null values at the front of the array are omitted from the final result"
+reimplements = "c6cf26de-8ccd-4410-84bd-b9efd88fd2bc"
+
+[382c5242-587e-4577-b8ce-a5fb51e385a1]
+description = "consecutive null values in the middle of the list are omitted from the final result"
+include = false
+
+[6991836d-0d9b-4703-80a0-3f1f23eb5981]
+description = "consecutive null values in the middle of the array are omitted from the final result"
+reimplements = "382c5242-587e-4577-b8ce-a5fb51e385a1"
+
+[ef1d4790-1b1e-4939-a179-51ace0829dbd]
+description = "6 level nest list with null values"
+include = false
+
+[dc90a09c-5376-449c-a7b3-c2d20d540069]
+description = "6 level nested array with null values"
+reimplements = "ef1d4790-1b1e-4939-a179-51ace0829dbd"
+
+[85721643-705a-4150-93ab-7ae398e2942d]
+description = "all values in nested list are null"
+include = false
+
+[51f5d9af-8f7f-4fb5-a156-69e8282cb275]
+description = "all values in nested array are null"
+reimplements = "85721643-705a-4150-93ab-7ae398e2942d"

exercises/practice/flatten-array/create_fixture.sql

@@ -0,0 +1,11 @@
+DROP TABLE IF EXISTS "flatten-array";
+CREATE TABLE "flatten-array" (
+  array  TEXT NOT NULL,    -- json array
+  result TEXT              -- json array
+);
+
+.mode csv
+.import ./data.csv "flatten-array"
+
+UPDATE "flatten-array" SET result = NULL;
+

exercises/practice/flatten-array/create_test_table.sql

@@ -0,0 +1,30 @@
+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
+  array TEXT NOT NULL,       -- json array
+  expected TEXT NOT NULL     -- json array
+);
+
+INSERT INTO tests (uuid, description, array, expected)
+VALUES
+('8c71dabd-da60-422d-a290-4a571471fb14', 'empty', '[]', '[]'),
+('d268b919-963c-442d-9f07-82b93f1b518c', 'no nesting', '[0,1,2]', '[0,1,2]'),
+('3f15bede-c856-479e-bb71-1684b20c6a30', 'flattens a nested array', '[[[]]]', '[]'),
+('c84440cc-bb3a-48a6-862c-94cf23f2815d', 'flattens array with just integers present', '[1,[2,3,4,5,6,7],8]', '[1,2,3,4,5,6,7,8]'),
+('d3d99d39-6be5-44f5-a31d-6037d92ba34f', '5 level nesting', '[0,2,[[2,3],8,100,4,[[[50]]]],-2]', '[0,2,2,3,8,100,4,50,-2]'),
+('d572bdba-c127-43ed-bdcd-6222ac83d9f7', '6 level nesting', '[1,[2,[[3]],[4,[[5]]],6,7],8]', '[1,2,3,4,5,6,7,8]'),
+('0705a8e5-dc86-4cec-8909-150c5e54fa9c', 'null values are omitted from the final result', '[1,2,null]', '[1,2]'),
+('bc72da10-5f55-4ada-baf3-50e4da02ec8e', 'consecutive null values at the front of the array are omitted from the final result', '[null,null,3]', '[3]'),
+('6991836d-0d9b-4703-80a0-3f1f23eb5981', 'consecutive null values in the middle of the array are omitted from the final result', '[1,null,null,4]', '[1,4]'),
+('dc90a09c-5376-449c-a7b3-c2d20d540069', '6 level nested array with null values', '[0,2,[[2,3],8,[[100]],null,[[null]]],-2]', '[0,2,2,3,8,100,-2]'),
+('51f5d9af-8f7f-4fb5-a156-69e8282cb275', 'all values in nested array are null', '[null,[[[null]]],null,null,[[null,null],null],null]', '[]');
+

exercises/practice/flatten-array/data.csv

@@ -0,0 +1,11 @@
+"[]",
+"[0,1,2]",
+"[[[]]]",
+"[1,[2,3,4,5,6,7],8]",
+"[0,2,[[2,3],8,100,4,[[[50]]]],-2]",
+"[1,[2,[[3]],[4,[[5]]],6,7],8]",
+"[1,2,null]",
+"[null,null,3]",
+"[1,null,null,4]",
+"[0,2,[[2,3],8,[[100]],null,[[null]]],-2]",
+"[null,[[[null]]],null,null,[[null,null],null],null]",

exercises/practice/flatten-array/flatten-array.sql

@@ -0,0 +1,5 @@
+-- Schema:
+-- CREATE TABLE "flatten-array" (
+--   array  TEXT NOT NULL,    -- json array
+--   result TEXT              -- json array
+-- );

exercises/practice/flatten-array/flatten-array_test.sql

@@ -0,0 +1,39 @@
+-- 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 ./flatten-array.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 array, result FROM "flatten-array") AS actual
+ WHERE (actual.array, JSON(actual.result)) =
+       (tests.array, JSON(tests.expected));
+
+-- Update message for failed tests to give helpful information:
+UPDATE tests
+   SET message = (
+        'Result for "' || tests.array || '"' || ' is <'
+        || COALESCE(actual.result, 'NULL')
+        || '> but should be <' || tests.expected || '>'
+      )
+  FROM (SELECT array, result FROM "flatten-array") AS actual
+ WHERE actual.array = tests.array 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;