Add 'change' exercise

config.json

@@ -559,6 +559,14 @@
         "prerequisites": [],
         "difficulty": 6
       },
+      {
+        "slug": "change",
+        "name": "Change",
+        "uuid": "2660ff89-57d1-453e-b616-b76ac01c7eb9",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
       {
         "slug": "connect",
         "name": "Connect",

exercises/practice/change/.docs/instructions.md

@@ -0,0 +1,14 @@
+# Instructions
+
+Correctly determine the fewest number of coins to be given to a customer such that the sum of the coins' value would equal the correct amount of change.
+
+## For example
+
+- An input of 15 with [1, 5, 10, 25, 100] should return one nickel (5) and one dime (10) or [5, 10]
+- An input of 40 with [1, 5, 10, 25, 100] should return one nickel (5) and one dime (10) and one quarter (25) or [5, 10, 25]
+
+## Edge cases
+
+- Does your algorithm work for any given set of coins?
+- Can you ask for negative change?
+- Can you ask for a change value smaller than the smallest coin value?

exercises/practice/change/.meta/Example.roc

@@ -0,0 +1,32 @@
+module [findFewestCoins]
+
+findFewestCoins : List U64, U64 -> Result (List U64) [NotFound]
+findFewestCoins = \coins, target ->
+    help = \sortedCoins, subTarget, maxLength ->
+        if subTarget == 0 then
+            Ok []
+        else if maxLength == 0 then
+            Err NotFound
+            else
+
+        when sortedCoins is
+            [] -> Err NotFound
+            [largestCoin, .. as otherCoins] ->
+                if largestCoin == subTarget then
+                    Ok [largestCoin]
+                else if largestCoin < subTarget then
+                    when help sortedCoins (subTarget - largestCoin) (maxLength - 1) is
+                        Ok otherCoinsWith ->
+                            coinsWith = otherCoinsWith |> List.append largestCoin
+                            when help otherCoins subTarget (List.len coinsWith - 1) is
+                                Ok coinsWithout -> Ok coinsWithout
+                                Err NotFound -> Ok coinsWith
+
+                        Err NotFound -> help otherCoins subTarget maxLength
+                else
+                    help otherCoins subTarget maxLength
+
+    help? (coins |> List.sortDesc) target Num.maxU64
+        |> List.sortAsc
+        |> Ok
+

exercises/practice/change/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ageron"
+  ],
+  "files": {
+    "solution": [
+      "Change.roc"
+    ],
+    "test": [
+      "change-test.roc"
+    ],
+    "example": [
+      ".meta/Example.roc"
+    ]
+  },
+  "blurb": "Correctly determine change to be given using the least number of coins.",
+  "source": "Software Craftsmanship - Coin Change Kata",
+  "source_url": "https://web.archive.org/web/20130115115225/http://craftsmanship.sv.cmu.edu:80/exercises/coin-change-kata"
+}

exercises/practice/change/.meta/template.j2

@@ -0,0 +1,18 @@
+{%- import "generator_macros.j2" as macros with context -%}
+{{ macros.canonical_ref() }}
+{{ macros.header() }}
+
+import {{ exercise | to_pascal }} exposing [{{ cases[0]["property"] | to_camel }}]
+
+{% for case in cases -%}
+# {{ case["description"] }}
+expect
+    coins = {{ case["input"]["coins"] | to_roc }}
+    result = coins |> {{ case["property"] | to_camel }} {{ case["input"]["target"] }}
+    {%- if case["expected"]["error"] %}
+    result |> Result.isErr
+    {%- else %}
+    result == Ok {{ case["expected"] | to_roc }}
+    {%- endif %}
+
+{% endfor %}

exercises/practice/change/.meta/tests.toml

@@ -0,0 +1,50 @@
+# 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.
+
+[d0ebd0e1-9d27-4609-a654-df5c0ba1d83a]
+description = "change for 1 cent"
+
+[36887bea-7f92-4a9c-b0cc-c0e886b3ecc8]
+description = "single coin change"
+
+[cef21ccc-0811-4e6e-af44-f011e7eab6c6]
+description = "multiple coin change"
+
+[d60952bc-0c1a-4571-bf0c-41be72690cb3]
+description = "change with Lilliputian Coins"
+
+[408390b9-fafa-4bb9-b608-ffe6036edb6c]
+description = "change with Lower Elbonia Coins"
+
+[7421a4cb-1c48-4bf9-99c7-7f049689132f]
+description = "large target values"
+
+[f79d2e9b-0ae3-4d6a-bb58-dc978b0dba28]
+description = "possible change without unit coins available"
+
+[9a166411-d35d-4f7f-a007-6724ac266178]
+description = "another possible change without unit coins available"
+
+[ce0f80d5-51c3-469d-818c-3e69dbd25f75]
+description = "a greedy approach is not optimal"
+
+[bbbcc154-e9e9-4209-a4db-dd6d81ec26bb]
+description = "no coins make 0 change"
+
+[c8b81d5a-49bd-4b61-af73-8ee5383a2ce1]
+description = "error testing for change smaller than the smallest of coins"
+
+[3c43e3e4-63f9-46ac-9476-a67516e98f68]
+description = "error if no combination can add up to target"
+
+[8fe1f076-9b2d-4f44-89fe-8a6ccd63c8f3]
+description = "cannot find negative change values"
+include = false

exercises/practice/change/Change.roc

@@ -0,0 +1,5 @@
+module [findFewestCoins]
+
+findFewestCoins : List U64, U64 -> Result (List U64) _
+findFewestCoins = \coins, target ->
+    crash "Please implement the 'findFewestCoins' function"

exercises/practice/change/change-test.roc

@@ -0,0 +1,84 @@
+# These tests are auto-generated with test data from:
+# https://github.com/exercism/problem-specifications/tree/main/exercises/change/canonical-data.json
+# File last updated on 2024-10-08
+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 Change exposing [findFewestCoins]
+
+# change for 1 cent
+expect
+    coins = [1, 5, 10, 25]
+    result = coins |> findFewestCoins 1
+    result == Ok [1]
+
+# single coin change
+expect
+    coins = [1, 5, 10, 25, 100]
+    result = coins |> findFewestCoins 25
+    result == Ok [25]
+
+# multiple coin change
+expect
+    coins = [1, 5, 10, 25, 100]
+    result = coins |> findFewestCoins 15
+    result == Ok [5, 10]
+
+# change with Lilliputian Coins
+expect
+    coins = [1, 4, 15, 20, 50]
+    result = coins |> findFewestCoins 23
+    result == Ok [4, 4, 15]
+
+# change with Lower Elbonia Coins
+expect
+    coins = [1, 5, 10, 21, 25]
+    result = coins |> findFewestCoins 63
+    result == Ok [21, 21, 21]
+
+# large target values
+expect
+    coins = [1, 2, 5, 10, 20, 50, 100]
+    result = coins |> findFewestCoins 999
+    result == Ok [2, 2, 5, 20, 20, 50, 100, 100, 100, 100, 100, 100, 100, 100, 100]
+
+# possible change without unit coins available
+expect
+    coins = [2, 5, 10, 20, 50]
+    result = coins |> findFewestCoins 21
+    result == Ok [2, 2, 2, 5, 10]
+
+# another possible change without unit coins available
+expect
+    coins = [4, 5]
+    result = coins |> findFewestCoins 27
+    result == Ok [4, 4, 4, 5, 5, 5]
+
+# a greedy approach is not optimal
+expect
+    coins = [1, 10, 11]
+    result = coins |> findFewestCoins 20
+    result == Ok [10, 10]
+
+# no coins make 0 change
+expect
+    coins = [1, 5, 10, 21, 25]
+    result = coins |> findFewestCoins 0
+    result == Ok []
+
+# error testing for change smaller than the smallest of coins
+expect
+    coins = [5, 10]
+    result = coins |> findFewestCoins 3
+    result |> Result.isErr
+
+# error if no combination can add up to target
+expect
+    coins = [5, 10]
+    result = coins |> findFewestCoins 94
+    result |> Result.isErr
+