2024 day 2

invalidusrname · invalidusrname · commit c9f54937d98a · 2024-12-02T22:11:13.000-05:00
diff --git a/2024/ruby/lib/advent_02_red_nosed_reports.rb b/2024/ruby/lib/advent_02_red_nosed_reports.rb
@@ -0,0 +1,53 @@
+class Report
+  attr_reader :levels
+
+  def initialize(levels)
+    @levels = levels
+  end
+
+  def initial_direction(levels)
+    levels.length > 1 && levels[0] < levels[1] ? 'increasing' : 'decreasing'
+  end
+
+  def safe_with_dampener?
+    return true if safe?
+
+    levels.each_index do |i|
+      dampered_levels = levels.dup
+      dampered_levels.delete_at(i)
+
+      direction = initial_direction(dampered_levels)
+
+      return true if safe_levels(direction, dampered_levels)
+    end
+
+    false
+  end
+
+  def safe_levels(direction, levels)
+    levels.each_index do |i|
+      next if i == 0
+
+      current = levels[i]
+      prev = levels[i - 1]
+
+      return false unless valid_direction?(direction, current, prev) && adjacent_safe?(prev, current)
+    end
+
+    true
+  end
+
+  def safe?
+    direction = initial_direction(levels)
+
+    safe_levels(direction, levels)
+  end
+
+  def valid_direction?(direction, level, prev)
+    (prev < level && direction == 'increasing') || (prev > level && direction == 'decreasing')
+  end
+
+  def adjacent_safe?(prev, level)
+    (prev - level).abs.between?(1, 3)
+  end
+end
diff --git a/2024/ruby/spec/advent_02_spec.rb b/2024/ruby/spec/advent_02_spec.rb
@@ -0,0 +1,85 @@
+require 'spec_helper'
+require 'pry'
+require 'advent_02_red_nosed_reports'
+
+describe "Report" do
+  context "with safe increasing levels" do
+    let(:levels) { [5, 6, 7, 8, 9, 10] }
+
+    it 'is safe' do
+      report = Report.new(levels)
+
+      expect(report.safe?).to be(true)
+    end
+  end
+
+  context "with safe decreasing levels" do
+    let(:levels) { [5, 4, 3, 2, 1] }
+
+    it 'is safe' do
+      report = Report.new(levels)
+
+      expect(report.safe?).to be(true)
+    end
+  end
+
+  context "with mixed levels" do
+    let(:levels) { [5, 4, 6] }
+
+    it 'is not safe' do
+      report = Report.new(levels)
+
+      expect(report.safe?).to be(false)
+    end
+  end
+
+  context "with bad adjacent levels" do
+    let(:levels) { [1, 2, 4, 8, 9] }
+
+    it 'is not safe' do
+      report = Report.new(levels)
+
+      expect(report.safe?).to be(false)
+    end
+  end
+
+  context "with sample data" do
+    let(:data) do
+      File.readlines('spec/fixtures/advent-02-sample.txt').map do |e|
+        e.chomp.split(' ').map(&:to_i)
+      end
+    end
+
+    it "calculates how many are safe" do
+      safe = data.select { |levels| Report.new(levels).safe? }
+
+      expect(safe.length).to be(2)
+    end
+
+    it "calculates how many are safe with a dampener of 1" do
+      safe = data.select { |levels| Report.new(levels).safe_with_dampener? }
+
+      expect(safe.length).to be(4)
+    end
+  end
+
+  context "with puzzle data" do
+    let(:data) do
+      File.readlines('spec/fixtures/advent-02.txt').map do |e|
+        e.chomp.split(' ').map(&:to_i)
+      end
+    end
+
+    it "calculates how many are safe" do
+      safe = data.select { |levels| Report.new(levels).safe? }
+
+      expect(safe.length).to be(660)
+    end
+
+    it "calculates how many are safe with a dampener of 1" do
+      safe = data.select { |levels| Report.new(levels).safe_with_dampener? }
+
+      expect(safe.length).to be(689)
+    end
+  end
+end
diff --git a/2024/ruby/spec/fixtures/advent-02-sample.txt b/2024/ruby/spec/fixtures/advent-02-sample.txt
@@ -0,0 +1,6 @@
+7 6 4 2 1
+1 2 7 8 9
+9 7 6 2 1
+1 3 2 4 5
+8 6 4 4 1
+1 3 6 7 9
diff --git a/2024/ruby/spec/fixtures/advent-02.txt b/2024/ruby/spec/fixtures/advent-02.txt
