Year 2023: Day 04

README.md

@@ -9,7 +9,7 @@ I'm also adding notes that may be useful if you're learning Ruby.
 Notes for solving:
 * [2015, complete](year_2015.md)
 * [2016, up to day 08](year_2016.md)
-* [2023, up to day 03](year_2023.md)
+* [2023, up to day 04](year_2023.md)
 
 # How to use
 Install dependencies with `bundle install`. If you are in a hurry, just install [RSpec](https://github.com/rspec/rspec-metagem) with `gem install rspec` and run `rspec` in the root directory.

spec/year_2015/day_04_spec.rb → spec/year_2023/day_04_spec.rb

@@ -1,9 +1,9 @@
-require 'year_2015/day_04'
+require 'year_2023/day_04'
 
-describe Year2015::Day04 do
+describe Year2023::Day04 do
   context 'when Part 1' do
     subject(:sample_one) do
-      described_class.new(File.read('spec/year_2015/day_04_sample_one'), true)
+      described_class.new(File.read('spec/year_2023/day_04_sample_one'), true)
     end
 
     it 'finds winning numbers' do
@@ -25,7 +25,7 @@
 
   context 'when Part 2' do
     subject(:sample_two) do
-      described_class.new(File.read('spec/year_2015/day_04_sample_one'))
+      described_class.new(File.read('spec/year_2023/day_04_sample_one'))
     end
 
     it 'distributes cards' do
@@ -41,7 +41,7 @@
 
   context 'when Results' do
     subject(:input_data) do
-      File.read('spec/year_2015/day_04_input')
+      File.read('spec/year_2023/day_04_input')
     end
 
     it 'correctly answers part 1' do

year_2023.md

@@ -77,4 +77,24 @@ I'm clearly not good enough with spatial representations (something about off-by
 
 Maybe I'll revisit this one with a better solution.
 
-Also, thanks to the kind people or [/r/adventofcode](https://www.reddit.com/r/adventofcode/comments/189q9wv/2023_day_3_another_sample_grid_to_use/) for the sample grids they provided, they were a great help in debugging the first part properly.
+Also, thanks to the kind people or [/r/adventofcode](https://www.reddit.com/r/adventofcode/comments/189q9wv/2023_day_3_another_sample_grid_to_use/) for the sample grids they provided, they were a great help in debugging the first part properly.
+
+## Day 04: Scratchcards
+
+```
+Year2015::Day04
+  Part 1
+    finds winning numbers
+    calculates points
+    gives a final result
+  Part 2
+    distributes cards
+    gives a final result
+  Results
+    correctly answers part 1
+    correctly answers part 2
+```
+
+Part one is pretty easy. One useful method is the [`#&`](https://ruby-doc.org/core-3.0.1/Array.html#method-i-26) operator that takes two arrays and returns a new one with only the matching contents. The syntax is clearly inspired by [bit masking](https://en.wikipedia.org/wiki/Mask_(computing)), which is a subject you should look into if you've never heard of it.
+
+Part two is a bit more annoying and requires to do a two-pass, but nothing really improbable.

year_2015/day_04.rb → year_2023/day_04.rb

@@ -1,4 +1,4 @@
-class Year2015
+class Year2023
   class Day04
     attr_reader :version, :lines