Add practice exercise: saddle-points

config.json

@@ -417,6 +417,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 8
+      },        
+      {
+        "slug": "saddle-points",
+        "name": "Saddle Points",
+        "uuid": "d050e56b-9f86-416c-baa3-10a98f47b944",  
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 8
       },
       {
         "slug": "scrabble-score",

exercises/practice/saddle-points/.docs/instructions.append.md

@@ -0,0 +1,12 @@
+# SQLite-specific instructions
+
+- The **matrix** column contains the input, a JSON-encoded array of arrays of integers.
+- The **result** columns should contain the output, the list of saddle points.
+  The output should be a JSON-encoded array of objects, each object has two keys: row and column.
+  For example, `[{"row": 2, "column": 1}]`.
+
+## JSON documentation
+
+See [JSON Functions And Operators][json-docs] for SQLite JSON functions.
+
+[json-docs]: https://www.sqlite.org/json1.html

exercises/practice/saddle-points/.docs/instructions.md

@@ -0,0 +1,27 @@
+# Instructions
+
+Your task is to find the potential trees where you could build your tree house.
+
+The data company provides the data as grids that show the heights of the trees.
+The rows of the grid represent the east-west direction, and the columns represent the north-south direction.
+
+An acceptable tree will be the largest in its row, while being the smallest in its column.
+
+A grid might not have any good trees at all.
+Or it might have one, or even several.
+
+Here is a grid that has exactly one candidate tree.
+
+```text
+      ↓
+      1  2  3  4
+    |-----------
+  1 | 9  8  7  8
+→ 2 |[5] 3  2  4
+  3 | 6  6  7  1
+```
+
+- Row 2 has values 5, 3, 2, and 4. The largest value is 5.
+- Column 1 has values 9, 5, and 6. The smallest value is 5.
+
+So the point at `[2, 1]` (row: 2, column: 1) is a great spot for a tree house.

exercises/practice/saddle-points/.docs/introduction.md

@@ -0,0 +1,11 @@
+# Introduction
+
+You plan to build a tree house in the woods near your house so that you can watch the sun rise and set.
+
+You've obtained data from a local survey company that show the height of every tree in each rectangular section of the map.
+You need to analyze each grid on the map to find good trees for your tree house.
+
+A good tree is both:
+
+- taller than every tree to the east and west, so that you have the best possible view of the sunrises and sunsets.
+- shorter than every tree to the north and south, to minimize the amount of tree climbing.

exercises/practice/saddle-points/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "jimmytty"
+  ],
+  "files": {
+    "solution": [
+      "saddle-points.sql"
+    ],
+    "test": [
+      "saddle-points_test.sql"
+    ],
+    "example": [
+      ".meta/example.sql"
+    ]
+  },
+  "blurb": "Detect saddle points in a matrix.",
+  "source": "J Dalbey's Programming Practice problems",
+  "source_url": "https://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html"
+}

exercises/practice/saddle-points/.meta/example.sql

@@ -0,0 +1,52 @@
+UPDATE "saddle-points"
+   SET result = (
+     WITH
+       jtree AS (
+         SELECT *,
+                SUBSTR(fullkey, 1, INSTR(fullkey, ']')) rowkey,
+                SUBSTR(fullkey, INSTR(fullkey, '][')) colkey
+           FROM JSON_TREE(matrix) j
+       ),
+       max_single_in_row AS (
+         SELECT MAX(value) value,
+                fullkey,
+                rowkey
+           FROM jtree
+          WHERE type = 'integer'
+          GROUP BY rowkey
+       ),
+       max_mult_in_row AS (
+         SELECT jtree.VALUE, jtree.fullkey, ms.rowkey
+           FROM max_single_in_row ms, jtree
+          WHERE ms.rowkey = jtree.rowkey
+            AND ms.value = jtree.value
+       ),
+       min_single_in_col AS (
+         SELECT MIN(value) value, fullkey, colkey
+           FROM jtree
+          WHERE type = 'integer'
+          GROUP BY colkey
+       ),
+       min_mult_in_col AS (
+         SELECT jtree.VALUE, jtree.fullkey, ms.colkey
+           FROM min_single_in_col ms, jtree
+          WHERE ms.colkey = jtree.colkey
+            AND ms.value = jtree.VALUE
+       ),
+       get_coords AS (
+         SELECT JSON(REPLACE(LTRIM(mc.fullkey, '$'), '][', ',')) coords
+           FROM max_mult_in_row mr,
+                min_mult_in_col mc
+          WHERE mr.fullkey = mc.fullkey
+       ),
+       to_objects AS (
+         SELECT JSON_OBJECT(
+           'row',    JSON_EXTRACT(coords, '$[0]') + 1,
+           'column', JSON_EXTRACT(coords, '$[1]') + 1
+         ) AS jobj
+           FROM get_coords
+       )
+     SELECT JSON_GROUP_ARRAY(JSON(jobj))
+       FROM to_objects
+     )
+;

exercises/practice/saddle-points/.meta/tests.toml

@@ -0,0 +1,37 @@
+# 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.
+
+[3e374e63-a2e0-4530-a39a-d53c560382bd]
+description = "Can identify single saddle point"
+
+[6b501e2b-6c1f-491f-b1bb-7f278f760534]
+description = "Can identify that empty matrix has no saddle points"
+
+[8c27cc64-e573-4fcb-a099-f0ae863fb02f]
+description = "Can identify lack of saddle points when there are none"
+
+[6d1399bd-e105-40fd-a2c9-c6609507d7a3]
+description = "Can identify multiple saddle points in a column"
+
+[3e81dce9-53b3-44e6-bf26-e328885fd5d1]
+description = "Can identify multiple saddle points in a row"
+
+[88868621-b6f4-4837-bb8b-3fad8b25d46b]
+description = "Can identify saddle point in bottom right corner"
+
+[5b9499ca-fcea-4195-830a-9c4584a0ee79]
+description = "Can identify saddle points in a non square matrix"
+
+[ee99ccd2-a1f1-4283-ad39-f8c70f0cf594]
+description = "Can identify that saddle points in a single column matrix are those with the minimum value"
+
+[63abf709-a84b-407f-a1b3-456638689713]
+description = "Can identify that saddle points in a single row matrix are those with the maximum value"

exercises/practice/saddle-points/create_fixture.sql

@@ -0,0 +1,10 @@
+DROP TABLE IF EXISTS "saddle-points";
+CREATE TABLE "saddle-points" (
+  matrix TEXT NOT NULL,    -- json array of arrays
+  result TEXT              -- json array of objects
+);
+
+.mode csv
+.import ./data.csv "saddle-points"
+
+UPDATE "saddle-points" SET result = NULL;

exercises/practice/saddle-points/create_test_table.sql

@@ -0,0 +1,27 @@
+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
+  matrix TEXT NOT NULL,     -- json array of arrays
+  expected TEXT NOT NULL    -- json array of objects
+);
+
+INSERT INTO tests (uuid, description, matrix, expected)
+VALUES
+  ('3e374e63-a2e0-4530-a39a-d53c560382bd', 'Can identify single saddle point', '[[9,8,7],[5,3,2],[6,6,7]]', '[{"row":2,"column":1}]'),
+  ('6b501e2b-6c1f-491f-b1bb-7f278f760534', 'Can identify that empty matrix has no saddle points', '[[]]', '[]'),
+  ('8c27cc64-e573-4fcb-a099-f0ae863fb02f', 'Can identify lack of saddle points when there are none', '[[1,2,3],[3,1,2],[2,3,1]]', '[]'),
+  ('6d1399bd-e105-40fd-a2c9-c6609507d7a3', 'Can identify multiple saddle points in a column', '[[4,5,4],[3,5,5],[1,5,4]]', '[{"row":1,"column":2},{"row":2,"column":2},{"row":3,"column":2}]'),
+  ('3e81dce9-53b3-44e6-bf26-e328885fd5d1', 'Can identify multiple saddle points in a row', '[[6,7,8],[5,5,5],[7,5,6]]', '[{"row":2,"column":1},{"row":2,"column":2},{"row":2,"column":3}]'),
+  ('88868621-b6f4-4837-bb8b-3fad8b25d46b', 'Can identify saddle point in bottom right corner', '[[8,7,9],[6,7,6],[3,2,5]]', '[{"row":3,"column":3}]'),
+  ('5b9499ca-fcea-4195-830a-9c4584a0ee79', 'Can identify saddle points in a non square matrix', '[[3,1,3],[3,2,4]]', '[{"row":1,"column":3},{"row":1,"column":1}]'),
+  ('ee99ccd2-a1f1-4283-ad39-f8c70f0cf594', 'Can identify that saddle points in a single column matrix are those with the minimum value', '[[2],[1],[4],[1]]', '[{"row":2,"column":1},{"row":4,"column":1}]'),
+  ('63abf709-a84b-407f-a1b3-456638689713', 'Can identify that saddle points in a single row matrix are those with the maximum value', '[[2,5,3,5]]', '[{"row":1,"column":2},{"row":1,"column":4}]');

exercises/practice/saddle-points/data.csv

@@ -0,0 +1,9 @@
+"[[9,8,7],[5,3,2],[6,6,7]]",
+"[[]]",
+"[[1,2,3],[3,1,2],[2,3,1]]",
+"[[4,5,4],[3,5,5],[1,5,4]]",
+"[[6,7,8],[5,5,5],[7,5,6]]",
+"[[8,7,9],[6,7,6],[3,2,5]]",
+"[[3,1,3],[3,2,4]]",
+"[[2],[1],[4],[1]]",
+"[[2,5,3,5]]",

exercises/practice/saddle-points/saddle-points.sql

@@ -0,0 +1,6 @@
+-- Schema:
+-- CREATE TABLE "saddle-points" (
+--   matrix TEXT NOT NULL,    -- json array of arrays
+--   result TEXT              -- json array of object
+-- );
+-- Task: update the saddle-points table and set the result based on the matrix.

exercises/practice/saddle-points/saddle-points_test.sql

@@ -0,0 +1,57 @@
+-- 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 ./saddle-points.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 matrix, result FROM "saddle-points") AS actual
+ WHERE actual.matrix = tests.matrix
+   AND IIF(
+         actual.matrix ISNULL, (
+         SELECT JSON_GROUP_ARRAY(JSON(value))
+           FROM (
+             SELECT j.value
+               FROM JSON_EACH(actual.result) j
+              ORDER BY j.VALUE
+           )
+         ),
+         actual.result
+       ) = (
+       SELECT JSON_GROUP_ARRAY(JSON(value))
+         FROM (
+           SELECT j.VALUE
+             FROM JSON_EACH(tests.expected) j
+            ORDER BY j.VALUE
+         )
+       )
+;
+
+-- Update message for failed tests to give helpful information:
+UPDATE tests
+   SET message = (
+         'Result for "' || tests.matrix || '"'
+         || ' is <' || COALESCE(actual.result, 'NULL')
+         || '> but should be <' || tests.expected || '>'
+       )
+  FROM (SELECT matrix, result FROM "saddle-points") AS actual
+ WHERE actual.matrix = tests.matrix 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;