Add zebra-puzzle exercise (#60)

Author: keiravillekode

config.json

@@ -424,6 +424,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 7
+      },
+      {
+        "slug": "zebra-puzzle",
+        "name": "Zebra Puzzle",
+        "uuid": "c317b776-57ef-4776-9a1e-70a928171e2d",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 10
       }
     ]
   },

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.fut"
+    ],
+    "test": [
+      "test.fut"
+    ],
+    "example": [
+      ".meta/example.fut"
+    ]
+  },
+  "blurb": "Solve the zebra puzzle.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Zebra_Puzzle"
+}

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

@@ -0,0 +1,114 @@
+
+def next_permutation [n] (a: *[n]i32): *[n]i32 =
+  -- Step 1. find j
+  let j = loop j = n - 2 while a[j] >= a[j + 1] do
+    j - 1
+  in
+
+    -- Step 2. increase a[j]
+    let l = loop l = n - 1 while a[j] >= a[l] do
+      l - 1
+    in
+      let aj = a[j]
+      let al = a[l]
+      let a = a with [j] = al with [l] = aj
+
+      -- Step 3. reverse a[j+1] ... a[n-1]
+      let (a, _, _) = loop (a, k, l) = (a, j + 1, n - 1) while k < l do
+        let ak = a[k]
+        let al = a[l]
+        in
+          (a with [k] = al with [l] = ak, k + 1, l - 1)
+      in
+        a
+
+def not_adjacent (i: i32) (j: i32): bool =
+  i + 1 != j && j + 1 != i
+
+type zebra_question = #drinks_water | #owns_zebra
+
+def answer(question: zebra_question): []u8 =
+  let (solution, _) = loop (solution, nationalities) = ("", [0, 1, 2, 3, 4, 5]) while length solution == 0 do
+    let englishman = nationalities[1]
+    let japanese = nationalities[2]
+    let norwegian = nationalities[3]
+    let spaniard = nationalities[4]
+    let ukrainian = nationalities[5]
+    in
+
+    -- 10. The Norwegian lives in the first house.
+    if norwegian != 1 then ("", next_permutation nationalities) else
+    let (solution2, _) = loop (solution2, colors) = ("", [0, 1, 2, 3, 4, 5]) while colors[0] == 0 && length solution2 == 0 do
+      let blue = colors[1]
+      let green = colors[2]
+      let ivory = colors[3]
+      let red = colors[4]
+      let yellow = colors[5]
+      in
+
+      -- 2. The Englishman lives in the red house.
+      -- 6. The green house is immediately to the right of the ivory house.
+      -- 15. The Norwegian lives next to the blue house.
+      if englishman != red || green != ivory + 1 || not_adjacent norwegian blue then ("", next_permutation colors) else
+      let (solution3, _) = loop (solution3, drinks) = ("", [0, 1, 2, 3, 4, 5]) while drinks[0] == 0 && length solution3 == 0 do
+        let coffee = drinks[1]
+        let milk = drinks[2]
+        let orangeJuice = drinks[3]
+        let tea = drinks[4]
+        let water = drinks[5]
+        in
+
+        -- 4. Coffee is drunk in the green house.
+        -- 5. The Ukrainian drinks tea.
+        -- 9. Milk is drunk in the middle house.
+        if coffee != green || ukrainian != tea || milk != 3 then ("", next_permutation drinks) else
+        let (solution4, _) = loop (solution4, hobbies) = ("", [0, 1, 2, 3, 4, 5]) while hobbies[0] == 0 && length solution4 == 0 do
+          let reading = hobbies[1]
+          let painting = hobbies[2]
+          let football = hobbies[3]
+          let dancing = hobbies[4]
+          let chess = hobbies[5]
+          in
+
+          -- 8. The person in the yellow house is a painter.
+          -- 13. The person who plays football drinks orange juice.
+          -- 14. The Japanese person plays chess.
+          if painting != yellow || football != orangeJuice || japanese != chess then ("", next_permutation hobbies) else
+          let (solution5, _) = loop (solution5, pets) = ("", [0, 1, 2, 3, 4, 5]) while pets[0] == 0 && length solution5 == 0 do
+            let dog = pets[1]
+            let fox = pets[2]
+            let horse = pets[3]
+            let snails = pets[4]
+            let zebra = pets[5]
+            let selection = match question
+              case #drinks_water -> water
+              case #owns_zebra -> zebra
+            in
+
+            -- 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 spaniard != dog || dancing != snails || not_adjacent reading fox || not_adjacent painting horse then ("", next_permutation pets) else
+            if selection == englishman then ("Englishman", [1]) else
+            if selection == japanese then ("Japanese", [1]) else
+            if selection == norwegian then ("Norwegian", [1]) else
+            if selection == spaniard then ("Spaniard", [1]) else
+            if selection == ukrainian then ("Ukrainian", [1]) else
+            assert false ("", [])
+          in
+            (solution5, next_permutation hobbies)
+        in
+          (solution4, next_permutation drinks)
+      in
+        (solution3, next_permutation colors)
+    in
+      (solution2, next_permutation nationalities)
+  in
+    solution
+
+def drinks_water: []u8 =
+  answer #drinks_water
+
+def owns_zebra: []u8 =
+  answer #owns_zebra

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/test.fut

@@ -0,0 +1,19 @@
+import "zebra_puzzle"
+
+-- resident who drinks water
+-- ==
+-- entry: test_drinks_water
+-- input {}
+-- output { "Norwegian" }
+
+-- resident who owns zebra
+-- ==
+-- entry: test_owns_zebra
+-- input {}
+-- output { "Japanese" }
+
+entry test_drinks_water: []u8 =
+  drinks_water
+
+entry test_owns_zebra: []u8 =
+  owns_zebra

exercises/practice/zebra-puzzle/zebra_puzzle.fut

@@ -0,0 +1,3 @@
+def drinks_water: []u8 = ???
+
+def owns_zebra: []u8 = ???