Add zebra-puzzle exercise (#643)

Author: keiravillekode

bin/add-practice-exercise

@@ -67,7 +67,7 @@ fi
 ./bin/fetch-configlet
 ./bin/configlet create --practice-exercise "${slug}" --author "${author}" --difficulty "${difficulty}"
 
-filter='.exercises.practice = (.exercises.practice | sort_by(.difficulty, (.name|ascii_upcase))'
+filter='.exercises.practice = (.exercises.practice | sort_by(.difficulty, (.name|ascii_upcase)))'
 jq "${filter}" config.json > config.sorted && mv config.sorted config.json
 
 exercise_dir="exercises/practice/${slug}"

config.json

@@ -1459,6 +1459,14 @@
           "strings"
         ]
       },
+      {
+        "slug": "zebra-puzzle",
+        "name": "Zebra Puzzle",
+        "uuid": "87be2159-daf5-4a6f-b7e1-61dc93edb1e7",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 8
+      },
       {
         "slug": "pov",
         "name": "POV",

exercises/practice/zebra-puzzle/.busted

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

exercises/practice/zebra-puzzle/.docs/instructions.md

@@ -0,0 +1,32 @@
+# Instructions
+
+Your task is to solve the Zebra Puzzle to find the answer to these two questions:
+
+- Which of the residents drinks water?
+- Who owns the zebra?
+
+## Puzzle
+
+The following 15 statements are all known to be true:
+
+1. There are five houses.
+2. The Englishman lives in the red house.
+3. The Spaniard owns the dog.
+4. The person in the green house drinks coffee.
+5. The Ukrainian drinks tea.
+6. The green house is immediately to the right of the ivory house.
+7. The snail owner likes to go dancing.
+8. The person in the yellow house is a painter.
+9. The person in the middle house drinks milk.
+10. The Norwegian lives in the first house.
+11. The person who enjoys reading lives in the house next to the person with the fox.
+12. The painter's house is next to the house with the horse.
+13. The person who plays football drinks orange juice.
+14. The Japanese person plays chess.
+15. The Norwegian lives next to the blue house.
+
+Additionally, each of the five houses is painted a different color, and their inhabitants are of different national extractions, own different pets, drink different beverages and engage in different hobbies.
+
+~~~~exercism/note
+There are 24 billion (5!⁵ = 24,883,200,000) possible solutions, so try ruling out as many solutions as possible.
+~~~~

exercises/practice/zebra-puzzle/.docs/introduction.md

@@ -0,0 +1,15 @@
+# Introduction
+
+The Zebra Puzzle is a famous logic puzzle in which there are five houses, each painted a different color.
+The houses have different inhabitants, who have different nationalities, own different pets, drink different beverages and enjoy different hobbies.
+
+To help you solve the puzzle, you're given 15 statements describing the solution.
+However, only by combining the information in _all_ statements will you be able to find the solution to the puzzle.
+
+~~~~exercism/note
+The Zebra Puzzle is a [Constraint satisfaction problem (CSP)][constraint-satisfaction-problem].
+In such a problem, you have a set of possible values and a set of constraints that limit which values are valid.
+Another well-known CSP is Sudoku.
+
+[constraint-satisfaction-problem]: https://en.wikipedia.org/wiki/Constraint_satisfaction_problem
+~~~~

exercises/practice/zebra-puzzle/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "zebra-puzzle.lua"
+    ],
+    "test": [
+      "zebra-puzzle_spec.lua"
+    ],
+    "example": [
+      ".meta/example.lua"
+    ]
+  },
+  "blurb": "Solve the zebra puzzle.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Zebra_Puzzle"
+}

exercises/practice/zebra-puzzle/.meta/example.lua

@@ -0,0 +1,115 @@
+local zebra_puzzle = {}
+
+local function permutations(a)
+  local n
+
+  return function()
+    if not n then
+      n = #a
+      return a
+    end
+
+    -- Step 1. Find largest j such that a[j] > a[j + 1].
+    local j = n - 1
+    while j >= 1 and a[j] <= a[j + 1] do
+      j = j - 1
+    end
+    if j < 1 then
+      return nil
+    end
+
+    -- Step 2. Find largest l such that a[j] > a[l], then swap.
+    local l = n
+    while a[j] <= a[l] do
+      l = l - 1
+    end
+    a[j], a[l] = a[l], a[j]
+
+    -- Step 3. Reverse a[j+1] ... a[n].
+    local lo, hi = j + 1, n
+    while lo < hi do
+      a[lo], a[hi] = a[hi], a[lo]
+      lo = lo + 1
+      hi = hi - 1
+    end
+
+    return a
+  end
+end
+
+local function index_of(t, val)
+  for i, v in ipairs(t) do
+    if v == val then
+      return i
+    end
+  end
+  return nil
+end
+
+local function next_to(a, b)
+  return math.abs(a - b) == 1
+end
+
+local water_drinker, zebra_owner
+
+local function solve()
+  for colors in permutations({ 'yellow', 'red', 'ivory', 'green', 'blue' }) do
+    -- 6. The green house is immediately to the right of the ivory house.
+    if index_of(colors, 'green') == index_of(colors, 'ivory') + 1 then
+      for drinks in permutations({ 'water', 'tea', 'orange juice', 'milk', 'coffee' }) do
+        -- 4. Coffee is drunk in the green house.
+        -- 9. Milk is drunk in the middle house.
+        if index_of(drinks, 'coffee') == index_of(colors, 'green') and drinks[3] == 'milk' then
+          for hobbies in permutations({ 'reading', 'painting', 'football', 'dancing', 'chess' }) do
+            -- 8. The person in the yellow house is a painter.
+            -- 13. The person who plays football drinks orange juice.
+            if index_of(hobbies, 'painting') == index_of(colors, 'yellow') and index_of(hobbies, 'football') ==
+              index_of(drinks, 'orange juice') then
+              for nationalities in permutations({ 'Ukrainian', 'Spaniard', 'Norwegian', 'Japanese', 'Englishman' }) do
+                -- 10. The Norwegian lives in the first house.
+                -- 2. The Englishman lives in the red house.
+                -- 15. The Norwegian lives next to the blue house.
+                -- 5. The Ukrainian drinks tea.
+                -- 14. The Japanese person plays chess.
+                if nationalities[1] == 'Norwegian' and index_of(colors, 'red') == index_of(nationalities, 'Englishman') and
+                  next_to(index_of(nationalities, 'Norwegian'), index_of(colors, 'blue')) and index_of(drinks, 'tea') ==
+                  index_of(nationalities, 'Ukrainian') and index_of(hobbies, 'chess') ==
+                  index_of(nationalities, 'Japanese') then
+                  for pets in permutations({ 'zebra', 'snail', 'horse', 'fox', 'dog' }) do
+                    -- 3. The Spaniard owns the dog.
+                    -- 7. The snail owner likes to go dancing.
+                    -- 11. The person who enjoys reading lives in the house next to the person with the fox.
+                    -- 12. The painter's house is next to the house with the horse.
+                    if index_of(pets, 'dog') == index_of(nationalities, 'Spaniard') and index_of(pets, 'snail') ==
+                      index_of(hobbies, 'dancing') and next_to(index_of(hobbies, 'reading'), index_of(pets, 'fox')) and
+                      next_to(index_of(hobbies, 'painting'), index_of(pets, 'horse')) then
+                      return nationalities[index_of(drinks, 'water')], nationalities[index_of(pets, 'zebra')]
+                    end
+                  end
+                end
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end
+
+local function ensure_solved()
+  if not water_drinker then
+    water_drinker, zebra_owner = solve()
+  end
+end
+
+function zebra_puzzle.drinks_water()
+  ensure_solved()
+  return water_drinker
+end
+
+function zebra_puzzle.owns_zebra()
+  ensure_solved()
+  return zebra_owner
+end
+
+return zebra_puzzle

exercises/practice/zebra-puzzle/.meta/spec_generator.lua

@@ -0,0 +1,19 @@
+local function snake_case(str)
+  local s = str:gsub('%u', function(c)
+    return '_' .. c:lower()
+  end)
+  if s:sub(1, 1) == '_' then
+    s = s:sub(2)
+  end
+  return s
+end
+
+return {
+  module_name = 'zebra_puzzle',
+
+  generate_test = function(case)
+    local template = [[
+      assert.equal('%s', zebra_puzzle.%s())]]
+    return template:format(case.expected, snake_case(case.property))
+  end
+}

exercises/practice/zebra-puzzle/.meta/tests.toml

@@ -0,0 +1,16 @@
+# 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.
+
+[16efb4e4-8ad7-4d5e-ba96-e5537b66fd42]
+description = "resident who drinks water"
+
+[084d5b8b-24e2-40e6-b008-c800da8cd257]
+description = "resident who owns zebra"

exercises/practice/zebra-puzzle/zebra-puzzle.lua

@@ -0,0 +1,9 @@
+local zebra_puzzle = {}
+
+function zebra_puzzle.drinks_water()
+end
+
+function zebra_puzzle.owns_zebra()
+end
+
+return zebra_puzzle