Add saddle points practice exercise

README.md

@@ -49,9 +49,12 @@ Rename *bob.lua* to *example.lua*, and add the exercise to the [lua/config.json]
 Optionally, you can generate the spec from the upstream canonical data.
 To use the spec generator, create a file called `spec_generator.lua` in the `.meta/` directory of the exercise.
 This file should be a Lua module returning a table with two fields:
-- `module_name` - A string containing the name of the Lua variable to which the module under test will be bound
+- `module_name` - A string containing the name of the Lua variable to which the module under test will be bound.
 - `generate_test` - A function that returns a string representation of a test given the corresponding case from the canonical data.
 
+Optionally, a third field can be included:
+- `test_helpers` - A string that will be injected at the top of the outermost `describe` block. This can include helper functions that are used in multiple tests or other setup code.
+
 To use the test generator, run:
 
 ```shell

bin/generate-spec

@@ -41,6 +41,10 @@ local function process(node)
       table.insert(output, "describe('" .. node.description:lower() .. "', function()")
     else
       table.insert(output, "describe('" .. exercise_name .. "', function()")
+
+      if spec_generator.test_helpers then
+        table.insert(output, spec_generator.test_helpers)
+      end
     end
 
     local cases = {}

config.json

@@ -1343,6 +1343,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 5
+      },
+      {
+        "slug": "saddle-points",
+        "name": "Saddle Points",
+        "uuid": "1fe6b8c5-776f-4b32-aac3-9957a8fe7925",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
       }
     ]
   },

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

@@ -1,5 +1,7 @@
 {
-  "authors": ["ryanplusplus"],
+  "authors": [
+    "ryanplusplus"
+  ],
   "files": {
     "solution": [
       "rotational-cipher.lua"

exercises/practice/saddle-points/.busted

@@ -0,0 +1,5 @@
+return {
+  default = {
+    ROOT = { '.' }
+  }
+}

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

@@ -0,0 +1,26 @@
+# 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  <--- potential tree house at row 2, column 1, for tree with height 5
+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": [
+    "ryanplusplus"
+  ],
+  "files": {
+    "solution": [
+      "saddle-points.lua"
+    ],
+    "test": [
+      "saddle-points_spec.lua"
+    ],
+    "example": [
+      ".meta/example.lua"
+    ]
+  },
+  "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.lua

@@ -0,0 +1,32 @@
+return function(matrix)
+  if #matrix == 0 or #matrix[1] == 0 then
+    return {}
+  end
+
+  local row_max = {}
+  local column_min = {}
+
+  for row, row_values in ipairs(matrix) do
+    row_max[row] = math.max(table.unpack(row_values))
+  end
+
+  for column = 1, #matrix[1] do
+    local column_values = {}
+    for _, row_values in ipairs(matrix) do
+      table.insert(column_values, row_values[column])
+    end
+    column_min[column] = math.min(table.unpack(column_values))
+  end
+
+  local saddle_points = {}
+
+  for row = 1, #matrix do
+    for column = 1, #matrix[1] do
+      if matrix[row][column] == row_max[row] and matrix[row][column] == column_min[column] then
+        table.insert(saddle_points, { row = row, column = column })
+      end
+    end
+  end
+
+  return saddle_points
+end

exercises/practice/saddle-points/.meta/spec_generator.lua

@@ -0,0 +1,49 @@
+local map = function(t, f)
+  local mapped = {}
+  for i, v in ipairs(t) do
+    mapped[i] = f(v)
+  end
+  return mapped
+end
+
+local function render_matrix(matrix)
+  return table.concat(map(matrix, function(row)
+    return '{' .. table.concat(row, ', ') .. '}, --'
+  end), '\n')
+end
+
+local function render_result(result)
+  return table.concat(map(result, function(point)
+    return ('{ row = %s, column = %s }, --'):format(point.row, point.column)
+  end), '\n')
+end
+
+return {
+  module_name = 'saddle_points',
+
+  test_helpers = [[
+    local function assert_saddle_points_are_equal(expected, actual)
+      if #expected ~= #actual then
+        return false
+      end
+      for i = 1, #expected do
+        if expected[i].row ~= actual[i].row or expected[i].column ~= actual[i].column then
+          return false
+        end
+      end
+      return true
+    end
+  ]],
+
+  generate_test = function(case)
+    local template = [[
+      local matrix = {
+        %s
+      }
+      local expected = {
+        %s
+      }
+      assert_saddle_points_are_equal(expected, saddle_points(matrix))]]
+    return template:format(render_matrix(case.input.matrix), render_result(case.expected))
+  end
+}

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/saddle-points.lua

@@ -0,0 +1,3 @@
+return function(matrix)
+
+end

exercises/practice/saddle-points/saddle-points_spec.lua

@@ -0,0 +1,122 @@
+local saddle_points = require('saddle-points')
+
+describe('saddle-points', function()
+  local function assert_saddle_points_are_equal(expected, actual)
+    if #expected ~= #actual then
+      return false
+    end
+    for i = 1, #expected do
+      if expected[i].row ~= actual[i].row or expected[i].column ~= actual[i].column then
+        return false
+      end
+    end
+    return true
+  end
+
+  it('can identify single saddle point', function()
+    local matrix = {
+      { 9, 8, 7 }, --
+      { 5, 3, 2 }, --
+      { 6, 6, 7 } --
+    }
+    local expected = {
+      { row = 2, column = 1 } --
+    }
+    assert_saddle_points_are_equal(expected, saddle_points(matrix))
+  end)
+
+  it('can identify that empty matrix has no saddle points', function()
+    local matrix = {
+      {} --
+    }
+    local expected = {}
+    assert_saddle_points_are_equal(expected, saddle_points(matrix))
+  end)
+
+  it('can identify lack of saddle points when there are none', function()
+    local matrix = {
+      { 1, 2, 3 }, --
+      { 3, 1, 2 }, --
+      { 2, 3, 1 } --
+    }
+    local expected = {}
+    assert_saddle_points_are_equal(expected, saddle_points(matrix))
+  end)
+
+  it('can identify multiple saddle points in a column', function()
+    local matrix = {
+      { 4, 5, 4 }, --
+      { 3, 5, 5 }, --
+      { 1, 5, 4 } --
+    }
+    local expected = {
+      { row = 1, column = 2 }, --
+      { row = 2, column = 2 }, --
+      { row = 3, column = 2 } --
+    }
+    assert_saddle_points_are_equal(expected, saddle_points(matrix))
+  end)
+
+  it('can identify multiple saddle points in a row', function()
+    local matrix = {
+      { 6, 7, 8 }, --
+      { 5, 5, 5 }, --
+      { 7, 5, 6 } --
+    }
+    local expected = {
+      { row = 2, column = 1 }, --
+      { row = 2, column = 2 }, --
+      { row = 2, column = 3 } --
+    }
+    assert_saddle_points_are_equal(expected, saddle_points(matrix))
+  end)
+
+  it('can identify saddle point in bottom right corner', function()
+    local matrix = {
+      { 8, 7, 9 }, --
+      { 6, 7, 6 }, --
+      { 3, 2, 5 } --
+    }
+    local expected = {
+      { row = 3, column = 3 } --
+    }
+    assert_saddle_points_are_equal(expected, saddle_points(matrix))
+  end)
+
+  it('can identify saddle points in a non square matrix', function()
+    local matrix = {
+      { 3, 1, 3 }, --
+      { 3, 2, 4 } --
+    }
+    local expected = {
+      { row = 1, column = 3 }, --
+      { row = 1, column = 1 } --
+    }
+    assert_saddle_points_are_equal(expected, saddle_points(matrix))
+  end)
+
+  it('can identify that saddle points in a single column matrix are those with the minimum value', function()
+    local matrix = {
+      { 2 }, --
+      { 1 }, --
+      { 4 }, --
+      { 1 } --
+    }
+    local expected = {
+      { row = 2, column = 1 }, --
+      { row = 4, column = 1 } --
+    }
+    assert_saddle_points_are_equal(expected, saddle_points(matrix))
+  end)
+
+  it('can identify that saddle points in a single row matrix are those with the maximum value', function()
+    local matrix = {
+      { 2, 5, 3, 5 } --
+    }
+    local expected = {
+      { row = 1, column = 2 }, --
+      { row = 1, column = 4 } --
+    }
+    assert_saddle_points_are_equal(expected, saddle_points(matrix))
+  end)
+end)

exercises/practice/two-bucket/.meta/config.json

@@ -1,5 +1,7 @@
 {
-  "authors": ["ryanplusplus"],
+  "authors": [
+    "ryanplusplus"
+  ],
   "files": {
     "solution": [
       "two-bucket.lua"

exercises/practice/wordy/.meta/config.json

@@ -1,5 +1,7 @@
 {
-  "authors": ["ryanplusplus"],
+  "authors": [
+    "ryanplusplus"
+  ],
   "files": {
     "solution": [
       "wordy.lua"

exercises/practice/yacht/.meta/config.json

@@ -1,5 +1,7 @@
 {
-  "authors": ["ryanplusplus"],
+  "authors": [
+    "ryanplusplus"
+  ],
   "files": {
     "solution": [
       "yacht.lua"