Add perfect-numbers exercise (#136)

config.json

@@ -585,6 +585,16 @@
         ],
         "difficulty": 2
       },
+      {
+        "slug": "perfect-numbers",
+        "name": "Perfect Numbers",
+        "uuid": "e523fad6-9078-46d0-a540-e6af83dc0e59",
+        "practices": [],
+        "prerequisites": [
+          "numbers"
+        ],
+        "difficulty": 3
+      },
       {
         "slug": "pangram",
         "name": "Pangram",

exercises/practice/perfect-numbers/.docs/instructions.md

@@ -0,0 +1,24 @@
+# Instructions
+
+Determine if a number is perfect, abundant, or deficient based on
+Nicomachus' (60 - 120 CE) classification scheme for positive integers.
+
+The Greek mathematician [Nicomachus][nicomachus] devised a classification scheme for positive integers, identifying each as belonging uniquely to the categories of **perfect**, **abundant**, or **deficient** based on their [aliquot sum][aliquot-sum].
+The aliquot sum is defined as the sum of the factors of a number not including the number itself.
+For example, the aliquot sum of 15 is (1 + 3 + 5) = 9
+
+- **Perfect**: aliquot sum = number
+  - 6 is a perfect number because (1 + 2 + 3) = 6
+  - 28 is a perfect number because (1 + 2 + 4 + 7 + 14) = 28
+- **Abundant**: aliquot sum > number
+  - 12 is an abundant number because (1 + 2 + 3 + 4 + 6) = 16
+  - 24 is an abundant number because (1 + 2 + 3 + 4 + 6 + 8 + 12) = 36
+- **Deficient**: aliquot sum < number
+  - 8 is a deficient number because (1 + 2 + 4) = 7
+  - Prime numbers are deficient
+
+Implement a way to determine whether a given number is **perfect**.
+Depending on your language track, you may also need to implement a way to determine whether a given number is **abundant** or **deficient**.
+
+[nicomachus]: https://en.wikipedia.org/wiki/Nicomachus
+[aliquot-sum]: https://en.wikipedia.org/wiki/Aliquot_sum

exercises/practice/perfect-numbers/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ErikSchierboom"
+  ],
+  "files": {
+    "solution": [
+      "src/perfect_numbers.cljs"
+    ],
+    "test": [
+      "test/perfect_numbers_test.cljs"
+    ],
+    "example": [
+      ".meta/src/example.cljs"
+    ]
+  },
+  "blurb": "Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for positive integers.",
+  "source": "Taken from Chapter 2 of Functional Thinking by Neal Ford.",
+  "source_url": "https://www.oreilly.com/library/view/functional-thinking/9781449365509/"
+}

exercises/practice/perfect-numbers/.meta/src/example.cljs

@@ -0,0 +1,17 @@
+(ns perfect-numbers)
+
+(defn- get-divisors
+  "Utility function to get the divisors of a number"
+  [number]
+  (for [n (range 1 (inc (quot number 2))) :when (zero? (mod number n))]
+    n))
+
+(defn classify [number]
+  "Classifies a positive integer as deficient, abundant or perfect"
+  (if-not (pos? number)
+    (throw (js/Error. "Only positive numbers can be classified."))
+    (let [divisor-sum (apply + (get-divisors number))]
+      (cond
+        (> divisor-sum number) :abundant
+        (< divisor-sum number) :deficient
+        (= divisor-sum number) :perfect))))

exercises/practice/perfect-numbers/.meta/tests.toml

@@ -0,0 +1,42 @@
+# 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.
+
+[163e8e86-7bfd-4ee2-bd68-d083dc3381a3]
+description = "Smallest perfect number is classified correctly"
+
+[169a7854-0431-4ae0-9815-c3b6d967436d]
+description = "Medium perfect number is classified correctly"
+
+[ee3627c4-7b36-4245-ba7c-8727d585f402]
+description = "Large perfect number is classified correctly"
+
+[80ef7cf8-9ea8-49b9-8b2d-d9cb3db3ed7e]
+description = "Smallest abundant number is classified correctly"
+
+[3e300e0d-1a12-4f11-8c48-d1027165ab60]
+description = "Medium abundant number is classified correctly"
+
+[ec7792e6-8786-449c-b005-ce6dd89a772b]
+description = "Large abundant number is classified correctly"
+
+[e610fdc7-2b6e-43c3-a51c-b70fb37413ba]
+description = "Smallest prime deficient number is classified correctly"
+
+[0beb7f66-753a-443f-8075-ad7fbd9018f3]
+description = "Smallest non-prime deficient number is classified correctly"
+
+[1c802e45-b4c6-4962-93d7-1cad245821ef]
+description = "Medium deficient number is classified correctly"
+
+[47dd569f-9e5a-4a11-9a47-a4e91c8c28aa]
+description = "Large deficient number is classified correctly"
+
+[a696dec8-6147-4d68-afad-d38de5476a56]
+description = "Edge case (no factors other than itself) is classified correctly"
+
+[72445cee-660c-4d75-8506-6c40089dc302]
+description = "Zero is rejected (not a natural number)"
+
+[2d72ce2c-6802-49ac-8ece-c790ba3dae13]
+description = "Negative integer is rejected (not a natural number)"

exercises/practice/perfect-numbers/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/perfect-numbers/src/perfect_numbers.cljs

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

exercises/practice/perfect-numbers/test/perfect_numbers_test.cljs

@@ -0,0 +1,20 @@
+(ns perfect-numbers-test
+  (:require
+   [clojure.test :refer [deftest testing is]]
+   [perfect-numbers]))
+
+(deftest test-initialize-perfect-number
+  (testing "Negative numbers throw an exception"
+    (is (thrown? js/Error (perfect-numbers/classify -1)))))
+
+(deftest test-classify-deficient
+  (testing "13 is a deficient number"
+    (is (= :deficient (perfect-numbers/classify 13)))))
+
+(deftest test-classify-perfect
+  (testing "28 is a perfect number"
+    (is (= :perfect (perfect-numbers/classify 28)))))
+
+(deftest test-classify-abundant
+  (testing "12 is an abundant number"
+    (is (= :abundant (perfect-numbers/classify 12)))))