Add change exercise (#117)

config.json

@@ -341,7 +341,7 @@
         "uuid": "c895c0f5-0fe5-4ce1-a3a9-b6cd911d9275",
         "practices": [],
         "prerequisites": [
-          "lists",          
+          "lists",
           "numbers",
           "strings"
         ],
@@ -394,7 +394,7 @@
         ],
         "difficulty": 2
       },
-      { 
+      {
         "slug": "acronym",
         "name": "Acronym",
         "uuid": "e6147a0d-3000-4b3c-9a60-3f8800730691",
@@ -584,6 +584,17 @@
           "conditionals"
         ],
         "difficulty": 2
+      },
+      {
+        "slug": "change",
+        "name": "Change",
+        "uuid": "e1e76dc4-543f-4d1e-8727-a726ee5291ec",
+        "practices": [],
+        "prerequisites": [
+          "numbers",
+          "vectors"
+        ],
+        "difficulty": 3
       }
     ]
   },

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/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ErikSchierboom"
+  ],
+  "files": {
+    "solution": [
+      "src/change.cljs"
+    ],
+    "test": [
+      "test/change_test.cljs"
+    ],
+    "example": [
+      ".meta/src/example.cljs"
+    ]
+  },
+  "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/src/example.cljs

@@ -0,0 +1,24 @@
+(ns change)
+
+(def algo
+  (memoize (fn [amount coins]
+             (let [smaller (filter #(<= % amount) coins)]
+               (if (empty? smaller) [amount]
+                 (apply min-key
+                        count
+                        ; check if valid solution, i.e. the final amount was zero
+                        (filter (comp zero? first)
+                                (map
+                                  (fn [coin]
+                                    (concat
+                                      (algo (rem amount coin) smaller)
+                                      (repeat (quot amount coin) coin)))
+                                  smaller))))))))
+
+(defn issue [amount coins] 
+  (try
+    (let [[x & xs] (algo amount coins)]
+      (if (zero? x) xs
+        (throw (new js/Error "cannot change"))))
+    ; thrown by apply min-key if we don't have the right coins to issue change
+    (catch clojure.lang.ArityException e (throw (new js/Error "cannot change")))))

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

@@ -0,0 +1,36 @@
+# This is an auto-generated file. Regular comments will be removed when this
+# file is regenerated. Regenerating will not touch any manually added keys,
+# so comments can be added in a "comment" key.
+
+[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"
+
+[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/deps.edn

@@ -0,0 +1,10 @@
+{:deps
+ {org.clojure/clojure {:mvn/version "1.10.1"}
+  org.clojure/clojurescript {:mvn/version "1.10.773"}}
+
+ :aliases
+ {:test
+  {:extra-paths ["test"]
+   :extra-deps
+   {olical/cljs-test-runner {:mvn/version "3.8.0"}}
+   :main-opts ["-m" "cljs-test-runner.main"]}}}

exercises/practice/change/src/change.cljs

@@ -0,0 +1,5 @@
+(ns change)
+
+(defn issue [] ;; <- arglist goes here
+  ;; your code goes here
+)

exercises/practice/change/test/change_test.cljs

@@ -0,0 +1,38 @@
+(ns change-test
+  (:require [clojure.test :refer [deftest is]]
+            [change :refer [issue]]))
+
+(deftest single-coin-change
+  (is (= (issue 25 #{1 5 10 25 100})
+         '(25))))
+
+(deftest multiple-coin-change
+  (is (= (issue 15 #{1 5 10 25 100})
+         '(5 10))))
+
+(deftest change-with-lilliputian-coins
+  (is (= (issue 23 #{1 4 15 20 50})
+         '(4 4 15))))
+
+(deftest change-with-elbonia-coins
+  (is (= (issue 63 #{1 5 10 21 25})
+         '(21 21 21))))
+
+(deftest large-target-values
+  (is (= (issue 999 #{1 2 5 10 20 50 100})
+         '(2 2 5 20 20 50 100 100 100 100 100 100 100 100 100))))
+
+(deftest no-coins-make-zero-change
+  (is (empty? (issue 0 #{1, 5, 10, 21, 25}))))
+
+(deftest error-testing-for-change-smallet-than-the-smallest-coin
+  (is (thrown? js/Error #"cannot change"
+                        (issue 3 #{5 10}))))
+
+(deftest cannot-find-negative-change-values
+  (is (thrown? js/Error #"cannot change"
+                        (issue -5 #{1 2 5}))))
+
+(deftest error-testing-for-no-valid-change
+  (is (thrown? js/Error #"cannot change"
+                        (issue 10 #{20 8 3}))))