Add dominoes exercise (#104)

config.json

@@ -495,6 +495,14 @@
         "prerequisites": [],
         "difficulty": 7
       },
+      {
+        "slug": "dominoes",
+        "name": "Dominoes",
+        "uuid": "baeabe4e-6d9b-4fa5-b8a7-22b1977d840e",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 8
+      },
       {
         "slug": "grep",
         "name": "Grep",

exercises/practice/dominoes/.docs/instructions.md

@@ -0,0 +1,13 @@
+# Instructions
+
+Make a chain of dominoes.
+
+Compute a way to order a given set of dominoes in such a way that they form a correct domino chain (the dots on one half of a stone match the dots on the neighboring half of an adjacent stone) and that dots on the halves of the stones which don't have a neighbor (the first and last stone) match each other.
+
+For example given the stones `[2|1]`, `[2|3]` and `[1|3]` you should compute something
+like `[1|2] [2|3] [3|1]` or `[3|2] [2|1] [1|3]` or `[1|3] [3|2] [2|1]` etc, where the first and last numbers are the same.
+
+For stones `[1|2]`, `[4|1]` and `[2|3]` the resulting chain is not valid: `[4|1] [1|2] [2|3]`'s first and last numbers are not the same.
+4 != 3
+
+Some test cases may use duplicate stones in a chain solution, assume that multiple Domino sets are being used.

exercises/practice/dominoes/.meta/Example.roc

@@ -0,0 +1,33 @@
+module [findChain]
+
+Domino : (U8, U8)
+
+findChain : List Domino -> Result (List Domino) [NoChainExists]
+findChain = \dominoes ->
+    help = \used, available ->
+        when available is
+            [] ->
+                when used is
+                    [] -> Ok []
+                    [single] ->
+                        if single.0 == single.1 then Ok used else Err NoChainExists
+
+                    [first, .., last] -> if first.0 == last.1 then Ok used else Err NoChainExists
+
+            [firstAvailable, .. as restAvailable] ->
+                when used is
+                    [] -> help [firstAvailable] restAvailable
+                    [.., lastUsed] ->
+                        available
+                        |> List.walkWithIndexUntil (Err NoChainExists) \_, domino, index ->
+                            maybeChain =
+                                if lastUsed.1 == domino.0 then
+                                    help (used |> List.append domino) (available |> List.dropAt index)
+                                else if lastUsed.1 == domino.1 then
+                                    help (used |> List.append (domino.1, domino.0)) (available |> List.dropAt index)
+                                else
+                                    Err NoChainExists
+                            when maybeChain is
+                                Ok chain -> Break (Ok chain)
+                                Err NoChainExists -> Continue (Err NoChainExists)
+    help [] dominoes

exercises/practice/dominoes/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "authors": [
+    "ageron"
+  ],
+  "files": {
+    "solution": [
+      "Dominoes.roc"
+    ],
+    "test": [
+      "dominoes-test.roc"
+    ],
+    "example": [
+      ".meta/Example.roc"
+    ]
+  },
+  "blurb": "Make a chain of dominoes."
+}

exercises/practice/dominoes/.meta/template.j2

@@ -0,0 +1,58 @@
+{%- import "generator_macros.j2" as macros with context -%}
+{{ macros.canonical_ref() }}
+{{ macros.header() }}
+
+import {{ exercise | to_pascal }} exposing [findChain]
+
+{% macro to_list_of_pairs(dominoes) -%}
+[
+{%- for domino in dominoes -%}
+({{ domino[0] }}, {{ domino[1] }}),
+{%- endfor -%}
+]
+{%- endmacro %}
+
+Domino : (U8, U8)
+
+## Rotate each domino if needed to ensure that the small side is on the left
+canonicalize : List Domino -> List Domino
+canonicalize = \dominoes ->
+    dominoes
+    |> List.map \domino ->
+        if domino.0 > domino.1 then (domino.1, domino.0) else domino
+
+## Ensure that the given result is Ok and is a valid chain for the
+## given list of dominoes
+isValidChainFor : Result (List Domino) _, List Domino -> Bool
+isValidChainFor = \maybeChain, dominoes ->
+    when maybeChain is
+        Err _ -> Bool.false
+        Ok chain ->
+            if Set.fromList (canonicalize chain) == Set.fromList (canonicalize dominoes) then
+                when chain is
+                    [] -> Bool.true
+                    [.., last] ->
+                        chain
+                        |> List.walkUntil (Ok last) \state, domino ->
+                            when state is
+                                Err InvalidChain -> crash "Unreachable"
+                                Ok previous ->
+                                    if previous.1 == domino.0 then
+                                        Continue (Ok domino)
+                                    else
+                                        Break (Err InvalidChain)
+                        |> Result.isOk
+            else
+                Bool.false
+
+{% for case in cases -%}
+# {{ case["description"] }}
+expect
+    result = findChain {{ to_list_of_pairs(case["input"]["dominoes"]) }}
+    {%- if case["expected"] %}
+    result |> isValidChainFor {{ to_list_of_pairs(case["input"]["dominoes"]) }}
+    {%- else %}
+    result |> Result.isErr
+    {%- endif %}
+
+{% endfor %}

exercises/practice/dominoes/.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.
+
+[31a673f2-5e54-49fe-bd79-1c1dae476c9c]
+description = "empty input = empty output"
+
+[4f99b933-367b-404b-8c6d-36d5923ee476]
+description = "singleton input = singleton output"
+
+[91122d10-5ec7-47cb-b759-033756375869]
+description = "singleton that can't be chained"
+
+[be8bc26b-fd3d-440b-8e9f-d698a0623be3]
+description = "three elements"
+
+[99e615c6-c059-401c-9e87-ad7af11fea5c]
+description = "can reverse dominoes"
+
+[51f0c291-5d43-40c5-b316-0429069528c9]
+description = "can't be chained"
+
+[9a75e078-a025-4c23-8c3a-238553657f39]
+description = "disconnected - simple"
+
+[0da0c7fe-d492-445d-b9ef-1f111f07a301]
+description = "disconnected - double loop"
+
+[b6087ff0-f555-4ea0-a71c-f9d707c5994a]
+description = "disconnected - single isolated"
+
+[2174fbdc-8b48-4bac-9914-8090d06ef978]
+description = "need backtrack"
+
+[167bb480-dfd1-4318-a20d-4f90adb4a09f]
+description = "separate loops"
+
+[cd061538-6046-45a7-ace9-6708fe8f6504]
+description = "nine elements"
+
+[44704c7c-3adb-4d98-bd30-f45527cf8b49]
+description = "separate three-domino loops"

exercises/practice/dominoes/Dominoes.roc

@@ -0,0 +1,7 @@
+module [findChain]
+
+Domino : (U8, U8)
+
+findChain : List Domino -> Result (List Domino) _
+findChain = \dominoes ->
+    crash "Please implement the 'findChain' function"

exercises/practice/dominoes/dominoes-test.roc

@@ -0,0 +1,110 @@
+# These tests are auto-generated with test data from:
+# https://github.com/exercism/problem-specifications/tree/main/exercises/dominoes/canonical-data.json
+# File last updated on 2024-09-21
+app [main] {
+    pf: platform "https://github.com/roc-lang/basic-cli/releases/download/0.15.0/SlwdbJ-3GR7uBWQo6zlmYWNYOxnvo8r6YABXD-45UOw.tar.br",
+}
+
+main =
+    Task.ok {}
+
+import Dominoes exposing [findChain]
+
+Domino : (U8, U8)
+
+## Rotate each domino if needed to ensure that the small side is on the left
+canonicalize : List Domino -> List Domino
+canonicalize = \dominoes ->
+    dominoes
+    |> List.map \domino ->
+        if domino.0 > domino.1 then (domino.1, domino.0) else domino
+
+## Ensure that the given result is Ok and is a valid chain for the
+## given list of dominoes
+isValidChainFor : Result (List Domino) _, List Domino -> Bool
+isValidChainFor = \maybeChain, dominoes ->
+    when maybeChain is
+        Err _ -> Bool.false
+        Ok chain ->
+            if Set.fromList (canonicalize chain) == Set.fromList (canonicalize dominoes) then
+                when chain is
+                    [] -> Bool.true
+                    [.., last] ->
+                        chain
+                        |> List.walkUntil (Ok last) \state, domino ->
+                            when state is
+                                Err InvalidChain -> crash "Unreachable"
+                                Ok previous ->
+                                    if previous.1 == domino.0 then
+                                        Continue (Ok domino)
+                                    else
+                                        Break (Err InvalidChain)
+                        |> Result.isOk
+            else
+                Bool.false
+
+# empty input = empty output
+expect
+    result = findChain []
+    result |> isValidChainFor []
+
+# singleton input = singleton output
+expect
+    result = findChain [(1, 1)]
+    result |> isValidChainFor [(1, 1)]
+
+# singleton that can't be chained
+expect
+    result = findChain [(1, 2)]
+    result |> Result.isErr
+
+# three elements
+expect
+    result = findChain [(1, 2), (3, 1), (2, 3)]
+    result |> isValidChainFor [(1, 2), (3, 1), (2, 3)]
+
+# can reverse dominoes
+expect
+    result = findChain [(1, 2), (1, 3), (2, 3)]
+    result |> isValidChainFor [(1, 2), (1, 3), (2, 3)]
+
+# can't be chained
+expect
+    result = findChain [(1, 2), (4, 1), (2, 3)]
+    result |> Result.isErr
+
+# disconnected - simple
+expect
+    result = findChain [(1, 1), (2, 2)]
+    result |> Result.isErr
+
+# disconnected - double loop
+expect
+    result = findChain [(1, 2), (2, 1), (3, 4), (4, 3)]
+    result |> Result.isErr
+
+# disconnected - single isolated
+expect
+    result = findChain [(1, 2), (2, 3), (3, 1), (4, 4)]
+    result |> Result.isErr
+
+# need backtrack
+expect
+    result = findChain [(1, 2), (2, 3), (3, 1), (2, 4), (2, 4)]
+    result |> isValidChainFor [(1, 2), (2, 3), (3, 1), (2, 4), (2, 4)]
+
+# separate loops
+expect
+    result = findChain [(1, 2), (2, 3), (3, 1), (1, 1), (2, 2), (3, 3)]
+    result |> isValidChainFor [(1, 2), (2, 3), (3, 1), (1, 1), (2, 2), (3, 3)]
+
+# nine elements
+expect
+    result = findChain [(1, 2), (5, 3), (3, 1), (1, 2), (2, 4), (1, 6), (2, 3), (3, 4), (5, 6)]
+    result |> isValidChainFor [(1, 2), (5, 3), (3, 1), (1, 2), (2, 4), (1, 6), (2, 3), (3, 4), (5, 6)]
+
+# separate three-domino loops
+expect
+    result = findChain [(1, 2), (2, 3), (3, 1), (4, 5), (5, 6), (6, 4)]
+    result |> Result.isErr
+