Day 8 - Puzzle 1

Author: ariejan

Gemfile

@@ -2,5 +2,6 @@ source 'https://rubygems.org'
 
 ruby '3.3.4'
 
+gem 'matrix'
 gem 'parallel', '~> 1.11', '>= 1.11.2'
 gem 'rspec'

Gemfile.lock

@@ -2,6 +2,7 @@ GEM
   remote: https://rubygems.org/
   specs:
     diff-lcs (1.5.1)
+    matrix (0.4.2)
     parallel (1.26.3)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
@@ -22,6 +23,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  matrix
   parallel (~> 1.11, >= 1.11.2)
   rspec
 

lib/input/day_08.txt

@@ -0,0 +1,50 @@
+..................................................
+.......................x.................N........
+..................x...............................
+............x................w.........D.....a....
+.........6...........i.........D..............u...
+........6.......................q................u
+........................i....u.w...........a.2....
+....................................u.12..........
+..................................f.....D....0a...
+.............................Q..D......c..N..f....
+..............w..................................f
+.........Y.............i...............q..a.......
+............................2..........O...q......
+.....6..G.....................R...................
+..............................N...................
+.U.......G................i...J.............0.....
+Y..U................F......N......................
+.T......Y.............H.................2.P.......
+...............T.........F.8........H.............
+..T...............F...............l..............0
+................G.....e........18...Q.............
+.......................F....................O.....
+.....Y....U...................l....g..............
+U........9........................................
+.....................e..q..Q......................
+.......X........e......................1Q..O......
+............T.................gx......0..........t
+...................l......9........P..............
+.y...........9...............r.5.......j.P........
+..z.........d.........g......................H....
+................6.......r...........P.........O...
+.A........................8...r...................
+.4....W...Z...........9..................s..j.....
+.z..W.........y...........og......................
+..3.z.....R.....L....o.........................H..
+.......yZ.c..W.......p..............s.............
+............1..3.........L.........S..............
+.......Z..4............o.....S...........5.......s
+............c........l......7.....................
+.....4....p.........I.......t...........5........j
+.......c....h...........C..d......................
+......n..........C......L............E....j.......
+.X.W..........n....R......d.I...............5.....
+3.........Cn.........L...r.............e..........
+...A...........Z.p.....I..S.............s.......J.
+....................7.............S...X....J......
+........X.............o...........................
+........A....h.R.....7.t...I......................
+..A.4z......y.p..h.7...........Et.................
+................h........3..E..d.8................

lib/solutions/day_08.rb

@@ -0,0 +1,68 @@
+require 'matrix'
+
+class Day08
+  attr_accessor :grid, :w, :h, :nodes, :antinodes
+
+  def part_one(input)
+    parse_input(input)
+
+    @nodes.each_pair do |_node, coords|
+      find_antinodes(coords)
+    end
+
+    @antinodes.flatten.count(true)
+  end
+
+  def part_two(_input)
+    0
+  end
+
+  def mark_antinode(x, y)
+    @counter ||= 0
+    @counter += 1
+
+    # print "M #{@counter}: #{x}, #{y} (#{@w}x#{@h})"
+
+    if x < 0 || x >= @w || y < 0 || y >= @h
+      # puts '- OUT'
+      return
+    end
+
+    # puts ' - OK'
+
+    @antinodes[y][x] = true
+  end
+
+  def find_antinodes(coords)
+    # Loop through all coordinate pemutations
+    coords.permutation(2).to_a.each do |a, b|
+      dx = b[0] - a[0]
+      dy = b[1] - a[1]
+
+      mark_antinode(a[0] - dx, a[1] - dy)
+    end
+  end
+
+  def parse_input(input)
+    # Parse grid
+    @grid = input.split("\n").map(&:chars)
+    @w = @grid[0].size
+    @h = @grid.size
+
+    # Track visisted nodes
+    @visited = Array.new(@h) { Array.new(@w, false) }
+
+    # Find antenna locations
+    @nodes = {}
+    @grid.each_with_index do |row, y|
+      row.each_with_index do |cell, x|
+        if cell != '.'
+          @nodes[cell] ||= []
+          @nodes[cell] << [x, y]
+        end
+      end
+    end
+
+    @antinodes = Array.new(@h) { Array.new(@w, false) }
+  end
+end

spec/input/day_08_test.txt

@@ -0,0 +1,12 @@
+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............

spec/solutions/day_08_spec.rb

@@ -0,0 +1,18 @@
+require 'spec_helper'
+require 'solutions/day_08'
+
+RSpec.describe Day08 do
+  let(:input) { File.read(File.join(__dir__, '..', '..', 'spec', 'input', 'day_08_test.txt')).strip }
+
+  describe '#part_one' do
+    it 'calculates the correct solutions for part one' do
+      expect(subject.part_one(input)).to eq(14)
+    end
+  end
+
+  describe '#part_two' do
+    it 'calculates the correct solutions for part two' do
+      expect(subject.part_two(input)).to eq(0)
+    end
+  end
+end