Add prime-factors exercise

config.json

@@ -160,6 +160,14 @@
         ],
         "difficulty": 1
       },
+      {
+        "slug": "prime-factors",
+        "name": "Prime Factors",
+        "uuid": "0c48987b-b594-4bf6-8b65-ba696927cb04",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
+      },
       {
         "slug": "knapsack",
         "name": "Knapsack",

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.zig"
+    ],
+    "test": [
+      "test_prime_factors.zig"
+    ],
+    "example": [
+      ".meta/example.zig"
+    ]
+  },
+  "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.zig

@@ -0,0 +1,24 @@
+const std = @import("std");
+const mem = std.mem;
+
+pub fn factors(allocator: mem.Allocator, value: u64) mem.Allocator.Error![]u64 {
+    var list = std.ArrayList(u64).init(allocator);
+    errdefer list.deinit();
+    var number = value;
+    var p: u64 = 2;
+
+    while (number > 1) {
+        if (p * p > number) {
+            p = number;
+        }
+
+        if (number % p == 0) {
+            try list.append(p);
+            number /= p;
+        } else {
+            p += 1;
+        }
+    }
+
+    return list.toOwnedSlice();
+}

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.zig

@@ -0,0 +1,8 @@
+const std = @import("std");
+const mem = std.mem;
+
+pub fn factors(allocator: mem.Allocator, value: u64) mem.Allocator.Error![]u64 {
+    _ = allocator;
+    _ = value;
+    @compileError("please implement the factors function");
+}

exercises/practice/prime-factors/test_prime_factors.zig

@@ -0,0 +1,102 @@
+const std = @import("std");
+const testing = std.testing;
+
+const prime_factors = @import("prime_factors.zig");
+
+test "no factors" {
+    const expected = [_]u64{};
+    const actual = try prime_factors.factors(testing.allocator, 1);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "prime number" {
+    const expected = [_]u64{2};
+    const actual = try prime_factors.factors(testing.allocator, 2);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "another prime number" {
+    const expected = [_]u64{3};
+    const actual = try prime_factors.factors(testing.allocator, 3);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "square of a prime" {
+    const expected = [_]u64{ 3, 3 };
+    const actual = try prime_factors.factors(testing.allocator, 9);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "product of first prime" {
+    const expected = [_]u64{ 2, 2 };
+    const actual = try prime_factors.factors(testing.allocator, 4);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "cube of a prime" {
+    const expected = [_]u64{ 2, 2, 2 };
+    const actual = try prime_factors.factors(testing.allocator, 8);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "product of second prime" {
+    const expected = [_]u64{ 3, 3, 3 };
+    const actual = try prime_factors.factors(testing.allocator, 27);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "product of third prime" {
+    const expected = [_]u64{ 5, 5, 5, 5 };
+    const actual = try prime_factors.factors(testing.allocator, 625);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "product of first and second prime" {
+    const expected = [_]u64{ 2, 3 };
+    const actual = try prime_factors.factors(testing.allocator, 6);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "product of primes and non-primes" {
+    const expected = [_]u64{ 2, 2, 3 };
+    const actual = try prime_factors.factors(testing.allocator, 12);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "product of primes" {
+    const expected = [_]u64{ 5, 17, 23, 461 };
+    const actual = try prime_factors.factors(testing.allocator, 901255);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "factors include a large prime" {
+    const expected = [_]u64{ 11, 9539, 894119 };
+    const actual = try prime_factors.factors(testing.allocator, 93819012551);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "product of three large primes" {
+    const expected = [_]u64{ 2077681, 2099191, 2101243 };
+    const actual = try prime_factors.factors(testing.allocator, 9164464719174396253);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}
+
+test "one very large prime" {
+    const expected = [_]u64{4016465016163};
+    const actual = try prime_factors.factors(testing.allocator, 4016465016163);
+    defer testing.allocator.free(actual);
+    try testing.expectEqualSlices(u64, &expected, actual);
+}