Add prime-factors exercise (#45)

Author: keiravillekode

config.json

@@ -158,6 +158,14 @@
         "prerequisites": [],
         "difficulty": 3
       },
+      {
+        "slug": "prime-factors",
+        "name": "Prime Factors",
+        "uuid": "17b57129-15ca-49a6-80b9-19d7477bf590",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
+      },
       {
         "slug": "raindrops",
         "name": "Raindrops",

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": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "prime_factors.fut"
+    ],
+    "test": [
+      "test.fut"
+    ],
+    "example": [
+      ".meta/example.fut"
+    ]
+  },
+  "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.fut

@@ -0,0 +1,6 @@
+def factors (value: i32): []i32 =
+  let (_, _, a, i) = loop (n, p, a, i) = (value, 2, replicate 32 0, 0) while n > 1 do
+    if n % p != 0 then (n, p + 1, a, i) else
+    (n / p, p, a with [i] = p, i + 1)
+  in
+    a[0:i]

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

@@ -0,0 +1,47 @@
+# 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"
+include = false

exercises/practice/prime-factors/prime_factors.fut

@@ -0,0 +1 @@
+def factors (value: i32): []i32 = ???

exercises/practice/prime-factors/test.fut

@@ -0,0 +1,59 @@
+import "prime_factors"
+
+-- no factors
+-- ==
+-- input { 1 }
+-- output { empty([0]i32) }
+
+-- prime number
+-- ==
+-- input { 2 }
+-- output { [2] }
+
+-- another prime number
+-- ==
+-- input { 3 }
+-- output { [3] }
+
+-- square of a prime
+-- ==
+-- input { 9 }
+-- output { [3, 3] }
+
+-- product of first prime
+-- ==
+-- input { 4 }
+-- output { [2, 2] }
+
+-- cube of a prime
+-- ==
+-- input { 8 }
+-- output { [2, 2, 2] }
+
+-- product of second prime
+-- ==
+-- input { 27 }
+-- output { [3, 3, 3] }
+
+-- product of third prime
+-- ==
+-- input { 625 }
+-- output { [5, 5, 5, 5] }
+
+-- product of first and second prime
+-- ==
+-- input { 6 }
+-- output { [2, 3] }
+
+-- product of primes and non-primes
+-- ==
+-- input { 12 }
+-- output { [2, 2, 3] }
+
+-- product of primes
+-- ==
+-- input { 901255 }
+-- output { [5, 17, 23, 461] }
+
+let main (value: i32): []i32 =
+  factors value