Add killer-sudoku-helper exercise

config.json

@@ -787,6 +787,14 @@
         "prerequisites": [],
         "difficulty": 4
       },
+      {
+        "slug": "killer-sudoku-helper",
+        "name": "Killer Sudoku Helper",
+        "uuid": "2e07e358-7432-484d-83b5-ea813577e1a1",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
       {
         "slug": "linked-list",
         "name": "Linked List",

exercises/practice/killer-sudoku-helper/.busted

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+return {
+  default = {
+    ROOT = { '.' }
+  }
+}

exercises/practice/killer-sudoku-helper/.docs/instructions.md

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+# Instructions
+
+A friend of yours is learning how to solve Killer Sudokus (rules below) but struggling to figure out which digits can go in a cage.
+They ask you to help them out by writing a small program that lists all valid combinations for a given cage, and any constraints that affect the cage.
+
+To make the output of your program easy to read, the combinations it returns must be sorted.
+
+## Killer Sudoku Rules
+
+- [Standard Sudoku rules][sudoku-rules] apply.
+- The digits in a cage, usually marked by a dotted line, add up to the small number given in the corner of the cage.
+- A digit may only occur once in a cage.
+
+For a more detailed explanation, check out [this guide][killer-guide].
+
+## Example 1: Cage with only 1 possible combination
+
+In a 3-digit cage with a sum of 7, there is only one valid combination: 124.
+
+- 1 + 2 + 4 = 7
+- Any other combination that adds up to 7, e.g. 232, would violate the rule of not repeating digits within a cage.
+
+![Sudoku grid, with three killer cages that are marked as grouped together.
+The first killer cage is in the 3×3 box in the top left corner of the grid.
+The middle column of that box forms the cage, with the followings cells from top to bottom: first cell contains a 1 and a pencil mark of 7, indicating a cage sum of 7, second cell contains a 2, third cell contains a 5.
+The numbers are highlighted in red to indicate a mistake.
+The second killer cage is in the central 3×3 box of the grid.
+The middle column of that box forms the cage, with the followings cells from top to bottom: first cell contains a 1 and a pencil mark of 7, indicating a cage sum of 7, second cell contains a 2, third cell contains a 4.
+None of the numbers in this cage are highlighted and therefore don't contain any mistakes.
+The third killer cage follows the outside corner of the central 3×3 box of the grid.
+It is made up of the following three cells: the top left cell of the cage contains a 2, highlighted in red, and a cage sum of 7.
+The top right cell of the cage contains a 3.
+The bottom right cell of the cage contains a 2, highlighted in red. All other cells are empty.][one-solution-img]
+
+## Example 2: Cage with several combinations
+
+In a 2-digit cage with a sum 10, there are 4 possible combinations:
+
+- 19
+- 28
+- 37
+- 46
+
+![Sudoku grid, all squares empty except for the middle column, column 5, which has 8 rows filled.
+Each continguous two rows form a killer cage and are marked as grouped together.
+From top to bottom: first group is a cell with value 1 and a pencil mark indicating a cage sum of 10, cell with value 9.
+Second group is a cell with value 2 and a pencil mark of 10, cell with value 8.
+Third group is a cell with value 3 and a pencil mark of 10, cell with value 7.
+Fourth group is a cell with value 4 and a pencil mark of 10, cell with value 6.
+The last cell in the column is empty.][four-solutions-img]
+
+## Example 3: Cage with several combinations that is restricted
+
+In a 2-digit cage with a sum 10, where the column already contains a 1 and a 4, there are 2 possible combinations:
+
+- 28
+- 37
+
+19 and 46 are not possible due to the 1 and 4 in the column according to standard Sudoku rules.
+
+![Sudoku grid, all squares empty except for the middle column, column 5, which has 8 rows filled.
+The first row contains a 4, the second is empty, and the third contains a 1.
+The 1 is highlighted in red to indicate a mistake.
+The last 6 rows in the column form killer cages of two cells each.
+From top to bottom: first group is a cell with value 2 and a pencil mark indicating a cage sum of 10, cell with value 8.
+Second group is a cell with value 3 and a pencil mark of 10, cell with value 7.
+Third group is a cell with value 1, highlighted in red, and a pencil mark of 10, cell with value 9.][not-possible-img]
+
+## Trying it yourself
+
+If you want to give an approachable Killer Sudoku a go, you can try out [this puzzle][clover-puzzle] by Clover, featured by [Mark Goodliffe on Cracking The Cryptic on the 21st of June 2021][goodliffe-video].
+
+You can also find Killer Sudokus in varying difficulty in numerous newspapers, as well as Sudoku apps, books and websites.
+
+## Credit
+
+The screenshots above have been generated using [F-Puzzles.com](https://www.f-puzzles.com/), a Puzzle Setting Tool by Eric Fox.
+
+[sudoku-rules]: https://masteringsudoku.com/sudoku-rules-beginners/
+[killer-guide]: https://masteringsudoku.com/killer-sudoku/
+[one-solution-img]: https://assets.exercism.org/images/exercises/killer-sudoku-helper/example1.png
+[four-solutions-img]: https://assets.exercism.org/images/exercises/killer-sudoku-helper/example2.png
+[not-possible-img]: https://assets.exercism.org/images/exercises/killer-sudoku-helper/example3.png
+[clover-puzzle]: https://app.crackingthecryptic.com/sudoku/HqTBn3Pr6R
+[goodliffe-video]: https://youtu.be/c_NjEbFEeW0?t=1180

exercises/practice/killer-sudoku-helper/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "killer-sudoku-helper.lua"
+    ],
+    "test": [
+      "killer-sudoku-helper_spec.lua"
+    ],
+    "example": [
+      ".meta/example.lua"
+    ]
+  },
+  "blurb": "Write a tool that makes it easier to solve Killer Sudokus",
+  "source": "Created by Sascha Mann, Jeremy Walker, and BethanyG for the Julia track on Exercism.",
+  "source_url": "https://github.com/exercism/julia/pull/413"
+}

exercises/practice/killer-sudoku-helper/.meta/example.lua

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+local function clone(original)
+  local result = {}
+  for k, v in ipairs(original) do
+    result[k] = v
+  end
+  return result
+end
+
+local function combinations(sum, size, exclude)
+  local excluded = {}
+  local result = {}
+  local combination = {}
+
+  if exclude then
+    for _, v in ipairs(exclude) do
+      excluded[v] = true
+    end
+  end
+
+  local function search(total, count, start)
+    if count == 0 then
+      if total == 0 then
+        table.insert(result, clone(combination))
+      end
+
+      return
+    end
+
+    for number = start, 9 do
+      if not excluded[number] then
+        combination[size - count + 1] = number
+        search(total - number, count - 1, number + 1)
+      end
+    end
+  end
+
+  search(sum, size, 1)
+  return result
+end
+
+return { combinations = combinations }

exercises/practice/killer-sudoku-helper/.meta/spec_generator.lua

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+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_solutions(solutions)
+  return table.concat(map(solutions, function(solution)
+    return '{' .. table.concat(solution, ', ') .. '}, --'
+  end), '\n')
+end
+
+local function render_optional_exclude(exclude)
+  if #exclude == 0 then
+    return ''
+  end
+
+  return ', {' .. table.concat(exclude, ', ') .. '}'
+end
+
+return {
+  module_name = 'killer_sudoku_helper',
+
+  generate_test = function(case)
+    local template = [[
+      local expected = {
+        %s
+      }
+      assert.are.same(expected, killer_sudoku_helper.combinations(%d, %d%s))]]
+    return template:format(render_solutions(case.expected), case.input.cage.sum, case.input.cage.size,
+                           render_optional_exclude(case.input.cage.exclude))
+  end
+}

exercises/practice/killer-sudoku-helper/.meta/tests.toml

@@ -0,0 +1,49 @@
+# 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.
+
+[2aaa8f13-11b5-4054-b95c-a906e4d79fb6]
+description = "Trivial 1-digit cages -> 1"
+
+[4645da19-9fdd-4087-a910-a6ed66823563]
+description = "Trivial 1-digit cages -> 2"
+
+[07cfc704-f8aa-41b2-8f9a-cbefb674cb48]
+description = "Trivial 1-digit cages -> 3"
+
+[22b8b2ba-c4fd-40b3-b1bf-40aa5e7b5f24]
+description = "Trivial 1-digit cages -> 4"
+
+[b75d16e2-ff9b-464d-8578-71f73094cea7]
+description = "Trivial 1-digit cages -> 5"
+
+[bcbf5afc-4c89-4ff6-9357-07ab4d42788f]
+description = "Trivial 1-digit cages -> 6"
+
+[511b3bf8-186f-4e35-844f-c804d86f4a7a]
+description = "Trivial 1-digit cages -> 7"
+
+[bd09a60d-3aca-43bd-b6aa-6ccad01bedda]
+description = "Trivial 1-digit cages -> 8"
+
+[9b539f27-44ea-4ff8-bd3d-c7e136bee677]
+description = "Trivial 1-digit cages -> 9"
+
+[0a8b2078-b3a4-4dbd-be0d-b180f503d5c3]
+description = "Cage with sum 45 contains all digits 1:9"
+
+[2635d7c9-c716-4da1-84f1-c96e03900142]
+description = "Cage with only 1 possible combination"
+
+[a5bde743-e3a2-4a0c-8aac-e64fceea4228]
+description = "Cage with several combinations"
+
+[dfbf411c-737d-465a-a873-ca556360c274]
+description = "Cage with several combinations that is restricted"

exercises/practice/killer-sudoku-helper/killer-sudoku-helper.lua

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+local function combinations(sum, size, exclude)
+
+end
+
+return { combinations = combinations }

exercises/practice/killer-sudoku-helper/killer-sudoku-helper_spec.lua

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+local killer_sudoku_helper = require('killer-sudoku-helper')
+
+describe('killer-sudoku-helper', function()
+  describe('trivial 1-digit cages', function()
+    it('1', function()
+      local expected = {
+        { 1 } --
+      }
+      assert.are.same(expected, killer_sudoku_helper.combinations(1, 1))
+    end)
+
+    it('2', function()
+      local expected = {
+        { 2 } --
+      }
+      assert.are.same(expected, killer_sudoku_helper.combinations(2, 1))
+    end)
+
+    it('3', function()
+      local expected = {
+        { 3 } --
+      }
+      assert.are.same(expected, killer_sudoku_helper.combinations(3, 1))
+    end)
+
+    it('4', function()
+      local expected = {
+        { 4 } --
+      }
+      assert.are.same(expected, killer_sudoku_helper.combinations(4, 1))
+    end)
+
+    it('5', function()
+      local expected = {
+        { 5 } --
+      }
+      assert.are.same(expected, killer_sudoku_helper.combinations(5, 1))
+    end)
+
+    it('6', function()
+      local expected = {
+        { 6 } --
+      }
+      assert.are.same(expected, killer_sudoku_helper.combinations(6, 1))
+    end)
+
+    it('7', function()
+      local expected = {
+        { 7 } --
+      }
+      assert.are.same(expected, killer_sudoku_helper.combinations(7, 1))
+    end)
+
+    it('8', function()
+      local expected = {
+        { 8 } --
+      }
+      assert.are.same(expected, killer_sudoku_helper.combinations(8, 1))
+    end)
+
+    it('9', function()
+      local expected = {
+        { 9 } --
+      }
+      assert.are.same(expected, killer_sudoku_helper.combinations(9, 1))
+    end)
+  end)
+
+  it('cage with sum 45 contains all digits 1:9', function()
+    local expected = {
+      { 1, 2, 3, 4, 5, 6, 7, 8, 9 } --
+    }
+    assert.are.same(expected, killer_sudoku_helper.combinations(45, 9))
+  end)
+
+  it('cage with only 1 possible combination', function()
+    local expected = {
+      { 1, 2, 4 } --
+    }
+    assert.are.same(expected, killer_sudoku_helper.combinations(7, 3))
+  end)
+
+  it('cage with several combinations', function()
+    local expected = {
+      { 1, 9 }, --
+      { 2, 8 }, --
+      { 3, 7 }, --
+      { 4, 6 } --
+    }
+    assert.are.same(expected, killer_sudoku_helper.combinations(10, 2))
+  end)
+
+  it('cage with several combinations that is restricted', function()
+    local expected = {
+      { 2, 8 }, --
+      { 3, 7 } --
+    }
+    assert.are.same(expected, killer_sudoku_helper.combinations(10, 2, { 1, 4 }))
+  end)
+end)