From 98b831aec4ea4babe4a71b7bd5d90f2ac392ce81 Mon Sep 17 00:00:00 2001
From: it3x <it3x@noreply.codeberg.org>
Date: Sat, 27 Jun 2026 09:04:32 +0000
Subject: [PATCH] Refresh 005_arrays2 exercise

Updated the exercise to use SIMD. This allows us to
cross-reference the concept from 112_vectors back to 005_arrays2,
introducing a handy feature of vectors early on.

See #430
---
 exercises/005_arrays2.zig         | 18 ++++++++++++++++--
 exercises/112_vectors.zig         |  4 ++++
 patches/patches/005_arrays2.patch | 16 ++++++++++------
 rivendell/elrond.zig              |  2 --
 4 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/exercises/005_arrays2.zig b/exercises/005_arrays2.zig
index 07b9abe..1de9a36 100644
--- a/exercises/005_arrays2.zig
+++ b/exercises/005_arrays2.zig
@@ -26,8 +26,13 @@ pub fn main() void {
     // (Problem 2)
     // Please set this array using repetition.
     // It should result in: 1 0 0 1 1 0 0 1 1 0 0 1
-    const bit_pattern_unit = [_]u8{ ??? };
-    const bit_pattern: [3 * bit_pattern_unit.len]u8 = @bitCast(@as([3][bit_pattern_unit.len]u8, @splat(bit_pattern_unit)));
+    const bit_pattern_unit = ???;
+
+    // How long should the bit pattern be?
+    const len = ???;
+
+    // For now, don't worry about the use of SIMD.
+    const bit_pattern: [len]u8 = std.simd.repeat(len, bit_pattern_unit);
 
     // Okay, that's all of the problems. Let's see the results.
     //
@@ -53,3 +58,12 @@ pub fn main() void {
 
     std.debug.print("\n", .{});
 }
+
+// For the curious:
+//
+// The `std.simd.repeat` function takes a target length and a pattern,
+// and returns a vector filled with that pattern repeated to the
+// desired length.
+//
+// For example, `repeat(5, [_]u8{1, 2})` will return a vector
+// equivalent to `.{1, 2, 1, 2, 1}`.
diff --git a/exercises/112_vectors.zig b/exercises/112_vectors.zig
index 748c086..0c43f9c 100644
--- a/exercises/112_vectors.zig
+++ b/exercises/112_vectors.zig
@@ -145,3 +145,7 @@ pub fn main() void {
     print("Max difference (old fn): {d: >5.3}\n", .{mpd_old});
     print("Max difference (new fn): {d: >5.3}\n", .{mpd_new});
 }
+
+// Another cool feature of Vectors is repeating patterns.
+// Remember the arrays exercise from earlier where we created an array
+// by repeating a pattern? See `005_arrays2.zig`.
diff --git a/patches/patches/005_arrays2.patch b/patches/patches/005_arrays2.patch
index d1abb36..0c72bd7 100644
--- a/patches/patches/005_arrays2.patch
+++ b/patches/patches/005_arrays2.patch
@@ -1,6 +1,6 @@
---- exercises/005_arrays2.zig	2026-05-04 16:26:32.778330847 +0200
-+++ answers/005_arrays2.zig	2026-05-04 16:26:13.082917974 +0200
-@@ -21,12 +21,12 @@
+--- exercises/005_arrays2.zig	2026-06-27 09:03:29.918124920 +0000
++++ answers/005_arrays2.zig	2026-06-27 09:01:13.162138431 +0000
+@@ -21,15 +21,15 @@
      // (Problem 1)
      // Please set this array concatenating the two arrays above.
      // It should result in: 1 3 3 7
@@ -10,8 +10,12 @@
      // (Problem 2)
      // Please set this array using repetition.
      // It should result in: 1 0 0 1 1 0 0 1 1 0 0 1
--    const bit_pattern_unit = [_]u8{ ??? };
+-    const bit_pattern_unit = ???;
 +    const bit_pattern_unit = [_]u8{ 1, 0, 0, 1 };
-     const bit_pattern: [3 * bit_pattern_unit.len]u8 = @bitCast(@as([3][bit_pattern_unit.len]u8, @splat(bit_pattern_unit)));
  
-     // Okay, that's all of the problems. Let's see the results.
+     // How long should the bit pattern be?
+-    const len = ???;
++    const len = 3 * bit_pattern_unit.len;
+ 
+     // For now, don't worry about the use of SIMD.
+     const bit_pattern: [len]u8 = std.simd.repeat(len, bit_pattern_unit);
diff --git a/rivendell/elrond.zig b/rivendell/elrond.zig
index 371c16f..2d26ce9 100644
--- a/rivendell/elrond.zig
+++ b/rivendell/elrond.zig
@@ -599,8 +599,6 @@ const exercises = [_]Exercise{
         .main_file = "005_arrays2.zig",
         .output = "LEET: 1337, Bits: 100110011001",
         .hint = "Fill in the two arrays.",
-        .skip = true,
-        .skip_hint = "Better solution is needed.",
     },
     .{
         .main_file = "006_strings.zig",