2025! Ruby, day 1

ruby/2025/1/bin/problem

@@ -0,0 +1,6 @@
+#/usr/bin/env ruby
+require "combination"
+
+combination = Combination.for STDIN.read.chomp
+puts "Part 1: #{combination.zero_count}"
+puts "Part 2: #{combination.zero_click_count}"

ruby/2025/1/lib/combination.rb

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+class Combination
+  attr_reader :steps
+  def initialize(steps)
+    @steps = steps
+  end
+
+  def self.for(string)
+    new string.split("\n").map{ |line| Step.for line }
+  end
+
+  def zero_count
+    safe = Safe.new
+    zc = 0
+    steps.each do |step|
+      safe.apply_step step
+      zc += 1 if safe.count.zero?
+    end
+    zc
+  end
+
+  def zero_click_count
+    safe = Safe.new
+    steps.each do |step|
+      safe.apply_step step
+    end
+    safe.zero_clicks
+  end
+
+  class Step
+    attr_reader :dir, :count
+    def initialize(dir, count)
+      @dir = dir
+      @count = dir == "R" ? count : -count
+    end
+
+    def self.for(string)
+      new string[0], string[1..].to_i
+    end
+  end
+
+  class Safe
+    attr_reader :count
+    attr_reader :zero_clicks
+    def initialize
+      @count = 50
+      @zero_clicks = 0
+    end
+
+    def apply_step(step)
+      if step.dir == "R"
+        0.upto(step.count - 1) do
+          @count += 1
+          @count = @count % 100
+          @zero_clicks += 1 if @count.zero?
+        end
+      else
+        0.upto(-step.count - 1) do
+          @count -= 1
+          @count = @count % 100
+          @zero_clicks += 1 if @count.zero?
+        end
+      end
+    end
+  end
+end

ruby/2025/1/test/test_combination.rb

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+require "minitest/autorun"
+require "combination"
+
+TEST_COMBINATION = <<END
+L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82
+END
+
+class TestCombination < Minitest::Test
+  def test_safe
+    safe = Combination::Safe.new
+    assert_equal 50, safe.count
+    assert_equal 0, safe.zero_clicks
+    safe.apply_step Combination::Step.for("L68")
+    assert_equal 82, safe.count
+    assert_equal 1, safe.zero_clicks
+    safe.apply_step Combination::Step.for("L30")
+    assert_equal 52, safe.count
+    assert_equal 1, safe.zero_clicks
+    safe.apply_step Combination::Step.for("R48")
+    assert_equal 0, safe.count
+    assert_equal 2, safe.zero_clicks
+    safe.apply_step Combination::Step.for("R300")
+    assert_equal 0, safe.count
+    assert_equal 5, safe.zero_clicks
+    safe.apply_step Combination::Step.for("L602")
+    assert_equal 98, safe.count
+    assert_equal 11, safe.zero_clicks
+
+    0.upto(99) do |count|
+      safe = Combination::Safe.new
+      safe.apply_step Combination::Step.for("L50")
+      safe.apply_step Combination::Step.new("R", count)
+      assert_equal count, safe.count
+      assert_equal 1, safe.zero_clicks
+    end
+  end
+
+  def test_zero_count
+    combination = Combination.for TEST_COMBINATION
+    assert_equal 3, combination.zero_count
+  end
+
+  def test_zero_clicks
+    combination = Combination.for TEST_COMBINATION
+    assert_equal 6, combination.zero_click_count
+
+    combination = Combination.for "R1000"
+    assert_equal 10, combination.zero_click_count
+  end
+end