2019: Day 8 Part 1

2019/day8/part1.rb

@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+class Layer
+  attr_reader :width, :height, :pixels
+  def initialize(width, height, pixels)
+    @width = width
+    @height = height
+    @pixels = pixels
+  end
+
+  def to_s
+    s = String.new
+    pixels.each_slice(@width) do |line|
+      s << line.join('')
+      s << "\n"
+    end
+    s
+  end
+end
+
+class SpaceImage
+  attr_reader :width, :height, :data
+
+  def initialize(width, height, data)
+    @width = width
+    @height = height
+    @data = data.strip.chars.map(&:to_i)
+    raise ArgumentError, 'bad data' unless (@data.size % (@width * @height)).zero?
+  end
+
+  def layers
+    return @layers unless @layers.nil?
+
+    @layers = []
+    @data.each_slice(@width * @height) do |layer|
+      @layers << Layer.new(@width, @height, layer)
+    end
+    @layers
+  end
+end
+
+input = File.read(File.join(__dir__, 'input'))
+img = SpaceImage.new(25, 6, input)
+
+target_layer = img.layers.min_by do |layer|
+  layer.pixels.count(&:zero?)
+end
+ones = target_layer.pixels.count { |p| p == 1 }
+twos = target_layer.pixels.count { |p| p == 2 }
+puts ones * twos