2024 day 5

2024/ruby/lib/advent_05_print_queue.rb

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+class DataReader
+  def initialize(file)
+    @lines = File.readlines(file).map(&:strip)
+  end
+
+  def empty_line_index
+    @lines.find_index { |line| line == "" }
+  end
+
+  def ordering_rules
+    @lines[0...empty_line_index] || []
+  end
+
+  def pages_to_produce
+    return [] unless empty_line_index
+
+    @lines[empty_line_index + 1..] || []
+  end
+
+  def create_rules
+    ordering_rules.map do |line|
+      Rule.new(*line.split("|").map(&:to_i))
+    end
+  end
+
+  def create_page_updates
+    pages_to_produce.map do |line|
+      PageUpdate.new(line.split(",").map(&:to_i))
+    end
+  end
+end
+
+class Rule
+  attr_reader :page, :before_page
+
+  def initialize(page, before_page)
+    @page = page
+    @before_page = before_page
+  end
+end
+
+class PageUpdate
+  attr_reader :numbers
+
+  def initialize(numbers)
+    @numbers = numbers
+  end
+
+  def middle_number
+    numbers.empty? ? nil : numbers[numbers.length / 2]
+  end
+end
+
+class RuleScanner
+  def initialize(rules, page_updates)
+    @rules = rules
+    @page_updates = page_updates
+  end
+
+  def valid_updates
+    @page_updates.select do |page_update|
+      orderer = Orderer.new(@rules, page_update)
+      orderer.in_order?
+    end
+  end
+
+  def invalid_updates
+    @page_updates.reject do |page_update|
+      orderer = Orderer.new(@rules, page_update)
+      orderer.in_order?
+    end
+  end
+
+  def valid_total
+    valid_updates.sum(&:middle_number)
+  end
+
+  def invalid_total
+    invalid_updates.map do |page_update|
+      orderer = Orderer.new(@rules, page_update)
+      orderer.reorder
+    end.sum(&:middle_number)
+  end
+end
+
+class Orderer
+  attr_reader :page_update
+
+  def initialize(rules, page_update)
+    @rules = rules
+    @page_update = page_update
+  end
+
+  def rules_for(number)
+    @rules.select { |r| r.page == number }
+  end
+
+  def scoped_rules_for(number)
+    rules_for(number).select { |r| page_update.numbers.include? r.before_page }
+  end
+
+  def lower_priority_pages_for(number)
+    scoped_rules_for(number).map(&:before_page).sort.uniq
+  end
+
+  def in_order?
+    numbers = page_update.numbers
+
+    numbers.each_with_index do |number, i|
+      rest = numbers[i + 1..]
+      return false unless lower_priority_pages_for(number).all? { |n| rest.include?(n) }
+    end
+
+    true
+  end
+
+  def reorder
+    numbers = page_update.numbers
+    return [] if numbers.empty?
+
+    numbers.sort! do |a, b|
+      lower_priority_pages_for(a).include?(b) ? -1 : 1
+    end
+
+    PageUpdate.new(numbers)
+  end
+end

2024/ruby/spec/advent_05_print_queue_spec.rb

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+require "spec_helper"
+require "advent_05_print_queue"
+
+describe "Puzzle" do
+  context "with sample data" do
+    let(:data) do
+      DataReader.new("./spec/fixtures/advent-05-sample.txt")
+    end
+
+    it "knows the ordering rules" do
+      result = data.ordering_rules
+
+      expected = [
+        "47|53", "97|13", "97|61", "97|47", "75|29", "61|13", "75|53",
+        "29|13", "97|29", "53|29", "61|53", "97|53", "61|29", "47|13",
+        "75|47", "97|75", "47|61", "75|61", "47|29", "75|13", "53|13"
+      ]
+
+      expect(result).to eq(expected)
+    end
+
+    it "knows the pages to produce" do
+      result = data.pages_to_produce
+
+      expected = %w[
+        75,47,61,53,29
+        97,61,53,29,13
+        75,29,13
+        75,97,47,61,53
+        61,13,29
+        97,13,75,29,47
+      ]
+
+      expect(result).to eq(expected)
+    end
+
+    it "knows the rules for a number" do
+      rules = data.create_rules
+      page_update = PageUpdate.new([])
+
+      orderer = Orderer.new(rules, page_update)
+
+      rules = orderer.rules_for(75)
+
+      before_numbers = rules.map(&:before_page).sort
+
+      expect(before_numbers).to eq([13, 29, 47, 53, 61])
+    end
+
+    it "knows which pages a number goes before" do
+      rules = data.create_rules
+      page_update = PageUpdate.new([75, 47, 61, 53, 29])
+
+      orderer = Orderer.new(rules, page_update)
+
+      expect(orderer.lower_priority_pages_for(75)).to eq([29, 47, 53, 61])
+    end
+
+    it "knows if a page update is in the right order" do
+      rules = data.create_rules
+      page_update = PageUpdate.new([75, 47, 61, 53, 29])
+
+      orderer = Orderer.new(rules, page_update)
+
+      expect(orderer.in_order?).to be(true)
+    end
+
+    it "knows if a page update is in the right order 2" do
+      rules = data.create_rules
+      page_update = PageUpdate.new([97, 61, 53, 29, 13])
+
+      orderer = Orderer.new(rules, page_update)
+
+      expect(orderer.in_order?).to be(true)
+    end
+
+    it "knows if a page update is in the right order 3" do
+      rules = data.create_rules
+      page_update = PageUpdate.new([75, 29, 13])
+
+      orderer = Orderer.new(rules, page_update)
+
+      expect(orderer.in_order?).to be(true)
+    end
+
+    it "knows when a page update is in the wrong order" do
+      rules = data.create_rules
+      page_update = PageUpdate.new([75, 97, 47, 61, 53])
+
+      orderer = Orderer.new(rules, page_update)
+
+      expect(orderer.in_order?).to be(false)
+    end
+
+    it "knows when a page update is in the wrong order 2" do
+      rules = data.create_rules
+      page_update = PageUpdate.new([61, 13, 29])
+
+      orderer = Orderer.new(rules, page_update)
+
+      expect(orderer.in_order?).to be(false)
+    end
+
+    it "knows when a page update is in the wrong order 3" do
+      rules = data.create_rules
+      page_update = PageUpdate.new([97, 13, 75, 29, 47])
+
+      orderer = Orderer.new(rules, page_update)
+
+      expect(orderer.in_order?).to be(false)
+    end
+
+    it "knows the correctly-ordered updates" do
+      rules = data.create_rules
+      page_updates = data.create_page_updates
+
+      scanner = RuleScanner.new(rules, page_updates)
+
+      valid = scanner.valid_updates
+
+      expect(valid.length).to be(3)
+
+      expect(valid[0].numbers).to eq([75, 47, 61, 53, 29])
+      expect(valid[0].middle_number).to eq(61)
+
+      expect(valid[1].numbers).to eq([97, 61, 53, 29, 13])
+      expect(valid[1].middle_number).to eq(53)
+
+      expect(valid[2].numbers).to eq([75, 29, 13])
+      expect(valid[2].middle_number).to eq(29)
+    end
+
+    it "knows how to reorder" do
+      rules = data.create_rules
+      page_update = PageUpdate.new([75, 97, 47, 61, 53])
+
+      orderer = Orderer.new(rules, page_update)
+
+      expect(orderer.reorder.numbers).to eq([97, 75, 47, 61, 53])
+    end
+  end
+
+  context "with puzzle data" do
+    let(:data) do
+      DataReader.new("./spec/fixtures/advent-05.txt")
+    end
+
+    it "solves part i" do
+      rules = data.create_rules
+      page_updates = data.create_page_updates
+
+      scanner = RuleScanner.new(rules, page_updates)
+
+      expect(scanner.valid_total).to eq(6260)
+    end
+
+    it "solves part ii" do
+      rules = data.create_rules
+      page_updates = data.create_page_updates
+
+      scanner = RuleScanner.new(rules, page_updates)
+
+      expect(scanner.invalid_total).to eq(5346)
+    end
+  end
+end

2024/ruby/spec/fixtures/advent-05-sample.txt

@@ -0,0 +1,28 @@
+47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47