add change

config.json

@@ -244,6 +244,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 4
+      },
+      {
+        "slug": "change",
+        "name": "Change",
+        "uuid": "12eb71ba-b6d0-4edf-af8f-8dbe195d1f27",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
       }
     ]
   },

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

@@ -0,0 +1,8 @@
+# Instructions
+
+Determine the fewest number of coins to give a customer so that the sum of their values equals the correct amount of change.
+
+## Examples
+
+- An amount of 15 with available coin values [1, 5, 10, 25, 100] should return one coin of value 5 and one coin of value 10, or [5, 10].
+- An amount of 40 with available coin values [1, 5, 10, 25, 100] should return one coin of value 5, one coin of value 10, and one coin of value 25, or [5, 10, 25].

exercises/practice/change/.docs/introduction.md

@@ -0,0 +1,26 @@
+# Introduction
+
+In the mystical village of Coinholt, you stand behind the counter of your bakery, arranging a fresh batch of pastries.
+The door creaks open, and in walks Denara, a skilled merchant with a keen eye for quality goods.
+After a quick meal, she slides a shimmering coin across the counter, representing a value of 100 units.
+
+You smile, taking the coin, and glance at the total cost of the meal: 88 units.
+That means you need to return 12 units in change.
+
+Denara holds out her hand expectantly.
+"Just give me the fewest coins," she says with a smile.
+"My pouch is already full, and I don't want to risk losing them on the road."
+
+You know you have a few options.
+"We have Lumis (worth 10 units), Viras (worth 5 units), and Zenth (worth 2 units) available for change."
+
+You quickly calculate the possibilities in your head:
+
+- one Lumis (1 × 10 units) + one Zenth (1 × 2 units) = 2 coins total
+- two Viras (2 × 5 units) + one Zenth (1 × 2 units) = 3 coins total
+- six Zenth (6 × 2 units) = 6 coins total
+
+"The best choice is two coins: one Lumis and one Zenth," you say, handing her the change.
+
+Denara smiles, clearly impressed.
+"As always, you've got it right."

exercises/practice/change/.gitignore

@@ -0,0 +1,2 @@
+node_modules
+**/*.res.js

exercises/practice/change/.meta/Change.res

@@ -0,0 +1,29 @@
+let findFewestCoins = (coins, target) => {
+  let table = Array.make(~length=target + 1, None)->(
+    t => {
+      t[0] = Some([])
+      t
+    }
+  )
+  let sorted = coins->Array.toSorted((a, b) => (a - b :> float))
+
+  for amt in 1 to target {
+    table[amt] =
+      sorted->Array.reduce(None, (best, coin) =>
+        switch (amt - coin, table->Array.get(amt - coin)->Option.flatMap(x => x)) {
+        | (r, Some(sub)) if r >= 0 =>
+          let path = Array.concat(sub, [coin])
+          switch best {
+          | Some(current) if Array.length(current) <= Array.length(path) => best
+          | _ => Some(path)
+          }
+        | _ => best
+        }
+      )
+  }
+
+  table
+  ->Array.get(target)
+  ->Option.flatMap(x => x)
+  ->Option.map(res => res->Array.toSorted((a, b) => (a - b :> float)))
+}

exercises/practice/change/.meta/Change.resi

@@ -0,0 +1 @@
+let findFewestCoins: (array<int>, int) => option<array<int>>

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

@@ -0,0 +1,21 @@
+{
+  "authors": [
+    "therealowenrees"
+  ],
+  "files": {
+    "solution": [
+      "src/Change.res",
+      "src/Change.resi"
+    ],
+    "test": [
+      "tests/Change_test.res"
+    ],
+    "example": [
+      ".meta/Change.res",
+      ".meta/Change.resi"
+    ]
+  },
+  "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/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.
+
+[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"

exercises/practice/change/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Exercism
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.