Day two

2.rb

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+#!/usr/bin/env ruby
+
+result = File.readlines("2.input").map(&:split).map { _1.map(&:to_i) }
+  .select do |v|
+    (v == v.sort || v == v.sort.reverse) &&
+      v.each_cons(2).map { _1.sort.inject(:-).abs }.all? { 1 <= _1 && _1 <= 3 }
+  end.size
+puts result
+
+require "rspec/autorun"
+class Report < Array
+  def self.from_line(line)
+    new(line.split.map(&:to_i))
+  end
+
+  def safe?
+    (increasing? || decreasing?) && within_limit?
+  end
+
+  def safe_with_dampener?
+    dampened.any?(&:safe?)
+  end
+
+  private
+
+  def dampened
+    size.times.map { Report.new(except(_1)) }
+  end
+
+  def except(v)
+    reject.with_index { |_, i| i == v }
+  end
+
+  def increasing?
+    self == sort
+  end
+
+  def decreasing?
+    self == sort.reverse
+  end
+
+  def within_limit?
+    each_cons(2)
+      .map { _1.sort.inject(:-).abs }
+      .all? { 1 <= _1 && _1 <= 3 }
+  end
+end
+
+input = File.readlines("2.input")
+
+puts "2-1"
+puts input
+  .map { Report.from_line(_1) }
+  .select(&:safe?)
+  .size
+puts "2-2"
+puts input
+  .map { Report.from_line(_1) }
+  .select(&:safe_with_dampener?)
+  .size
+
+describe Report do
+  [
+    "48 51 52 53 52",
+    "86 87 88 91 91",
+    "22 25 28 31 32 36",
+    "65 66 68 69 71 72 75 82"
+  ].each do |line|
+    it "returns safe? as false for #{line}" do
+      expect(Report.from_line(line).safe?).to eq(false)
+    end
+  end
+
+  [
+    "1 2 3 4 5 6 7",
+    "1 3 5 7 9",
+    "9 8 7",
+    "1 4 5 8"
+  ].each do |line|
+    it "returns safe? as true for #{line}" do
+      expect(Report.from_line(line).safe?).to eq(true)
+    end
+  end
+end

Gemfile

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+source "https://rubygems.org"
+
+gem "rspec"

Gemfile.lock

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+GEM
+  remote: https://rubygems.org/
+  specs:
+    diff-lcs (1.5.1)
+    rspec (3.13.0)
+      rspec-core (~> 3.13.0)
+      rspec-expectations (~> 3.13.0)
+      rspec-mocks (~> 3.13.0)
+    rspec-core (3.13.2)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.3)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.2)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-support (3.13.2)
+
+PLATFORMS
+  arm64-darwin-24
+  ruby
+
+DEPENDENCIES
+  rspec
+
+BUNDLED WITH
+   2.5.23