Add prime-factors (#353)

config.json

@@ -385,6 +385,14 @@
         "prerequisites": [],
         "difficulty": 3
       },
+      {
+        "slug": "prime-factors",
+        "name": "Prime Factors",
+        "uuid": "bd85cab1-c5e1-46ac-9faf-a815510fdfcd",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "protein-translation",
         "name": "Protein Translation",

exercises/practice/prime-factors/.docs/instructions.md

@@ -0,0 +1,36 @@
+# Instructions
+
+Compute the prime factors of a given natural number.
+
+A prime number is only evenly divisible by itself and 1.
+
+Note that 1 is not a prime number.
+
+## Example
+
+What are the prime factors of 60?
+
+- Our first divisor is 2.
+  2 goes into 60, leaving 30.
+- 2 goes into 30, leaving 15.
+  - 2 doesn't go cleanly into 15.
+    So let's move on to our next divisor, 3.
+- 3 goes cleanly into 15, leaving 5.
+  - 3 does not go cleanly into 5.
+    The next possible factor is 4.
+  - 4 does not go cleanly into 5.
+    The next possible factor is 5.
+- 5 does go cleanly into 5.
+- We're left only with 1, so now, we're done.
+
+Our successful divisors in that computation represent the list of prime factors of 60: 2, 2, 3, and 5.
+
+You can check this yourself:
+
+```text
+2 * 2 * 3 * 5
+= 4 * 15
+= 60
+```
+
+Success!

exercises/practice/prime-factors/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "prime-factors.coffee"
+    ],
+    "test": [
+      "prime-factors.spec.coffee"
+    ],
+    "example": [
+      ".meta/example.coffee"
+    ]
+  },
+  "blurb": "Compute the prime factors of a given natural number.",
+  "source": "The Prime Factors Kata by Uncle Bob",
+  "source_url": "https://web.archive.org/web/20221026171801/http://butunclebob.com/ArticleS.UncleBob.ThePrimeFactorsKata"
+}

exercises/practice/prime-factors/.meta/example.coffee

@@ -0,0 +1,12 @@
+class PrimeFactors
+  @factors: (value) ->
+    factors = []
+    divisor = 2
+    while value > 1
+      while value % divisor == 0
+        factors.push divisor
+        value /= divisor
+      divisor += 1
+    factors
+
+module.exports = PrimeFactors

exercises/practice/prime-factors/.meta/tests.toml

@@ -0,0 +1,46 @@
+# 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.
+
+[924fc966-a8f5-4288-82f2-6b9224819ccd]
+description = "no factors"
+
+[17e30670-b105-4305-af53-ddde182cb6ad]
+description = "prime number"
+
+[238d57c8-4c12-42ef-af34-ae4929f94789]
+description = "another prime number"
+
+[f59b8350-a180-495a-8fb1-1712fbee1158]
+description = "square of a prime"
+
+[756949d3-3158-4e3d-91f2-c4f9f043ee70]
+description = "product of first prime"
+
+[bc8c113f-9580-4516-8669-c5fc29512ceb]
+description = "cube of a prime"
+
+[7d6a3300-a4cb-4065-bd33-0ced1de6cb44]
+description = "product of second prime"
+
+[073ac0b2-c915-4362-929d-fc45f7b9a9e4]
+description = "product of third prime"
+
+[6e0e4912-7fb6-47f3-a9ad-dbcd79340c75]
+description = "product of first and second prime"
+
+[00485cd3-a3fe-4fbe-a64a-a4308fc1f870]
+description = "product of primes and non-primes"
+
+[02251d54-3ca1-4a9b-85e1-b38f4b0ccb91]
+description = "product of primes"
+
+[070cf8dc-e202-4285-aa37-8d775c9cd473]
+description = "factors include a large prime"

exercises/practice/prime-factors/prime-factors.coffee

@@ -0,0 +1,4 @@
+class PrimeFactors
+  @factors: (value) ->
+
+module.exports = PrimeFactors

exercises/practice/prime-factors/prime-factors.spec.coffee

@@ -0,0 +1,38 @@
+PrimeFactors = require './prime-factors'
+
+describe 'Prime Factors', ->
+  it 'no factors', ->
+      expect(PrimeFactors.factors 1).toEqual []
+
+  xit 'prime number', ->
+      expect(PrimeFactors.factors 2).toEqual [2]
+
+  xit 'another prime number', ->
+      expect(PrimeFactors.factors 3).toEqual [3]
+
+  xit 'square of a prime', ->
+      expect(PrimeFactors.factors 9).toEqual [3, 3]
+
+  xit 'product of first prime', ->
+      expect(PrimeFactors.factors 4).toEqual [2, 2]
+
+  xit 'cube of a prime', ->
+      expect(PrimeFactors.factors 8).toEqual [2, 2, 2]
+
+  xit 'product of second prime', ->
+      expect(PrimeFactors.factors 27).toEqual [3, 3, 3]
+
+  xit 'product of third prime', ->
+      expect(PrimeFactors.factors 625).toEqual [5, 5, 5, 5]
+
+  xit 'product of first and second prime', ->
+      expect(PrimeFactors.factors 6).toEqual [2, 3]
+
+  xit 'product of primes and non-primes', ->
+      expect(PrimeFactors.factors 12).toEqual [2, 2, 3]
+
+  xit 'product of primes', ->
+      expect(PrimeFactors.factors 901255).toEqual [5, 17, 23, 461]
+
+  xit 'factors include a large prime', ->
+      expect(PrimeFactors.factors 93819012551).toEqual [11, 9539, 894119]