From ca03e4367be9d5e96c5dc6de75e919d57fd2923e Mon Sep 17 00:00:00 2001
From: Bill Rossi <bassguitarbill@gmail.com>
Date: Sun, 7 Dec 2025 07:51:28 -0500
Subject: [PATCH] 2025 day 7

---
 ruby/2025/7/bin/problem               |  8 +++
 ruby/2025/7/lib/laboratories.rb       | 98 +++++++++++++++++++++++++++
 ruby/2025/7/test/test_laboratories.rb | 44 ++++++++++++
 3 files changed, 150 insertions(+)
 create mode 100644 ruby/2025/7/bin/problem
 create mode 100644 ruby/2025/7/lib/laboratories.rb
 create mode 100644 ruby/2025/7/test/test_laboratories.rb

diff --git a/ruby/2025/7/bin/problem b/ruby/2025/7/bin/problem
new file mode 100644
index 0000000..91fbffb
--- /dev/null
+++ b/ruby/2025/7/bin/problem
@@ -0,0 +1,8 @@
+#!/usr/bin/env ruby
+
+require "laboratories"
+
+lab = Laboratories.for STDIN.read.chomp
+
+puts "Part 1: #{lab.split_count}"
+puts "Part 2: #{lab.count_tachyon_lifetimes}"
\ No newline at end of file
diff --git a/ruby/2025/7/lib/laboratories.rb b/ruby/2025/7/lib/laboratories.rb
new file mode 100644
index 0000000..c323dc3
--- /dev/null
+++ b/ruby/2025/7/lib/laboratories.rb
@@ -0,0 +1,98 @@
+class Laboratories
+  attr_reader :layers
+  def initialize(layers)
+    @layers = layers
+  end
+
+  def self.for(input)
+    new input.split("\n").map(&Layer.method(:new))
+  end
+
+  def split_count
+    layers.reduce([layers.first.blank_beams, 0]) do |acc, layer|
+      out = layer.split_beams acc[0]
+      [out[0], out[1] + acc[1]]
+    end[1]
+  end
+
+  def count_tachyon_lifetimes
+    @memo = {}
+    count_lifetimes layers.first.line.index("S"), 0
+  end
+
+  def count_lifetimes(position, layer)
+    return @memo["#{position}/#{layer}"] if @memo.key? "#{position}/#{layer}"
+
+    lt = if layer >= layers.count
+      1
+    else
+      if layers[layer].line[position] == "^"
+        count_lifetimes(position - 1, layer + 1) + count_lifetimes(position + 1, layer + 1)
+      else
+        count_lifetimes position, layer + 1
+      end
+    end
+    @memo["#{position}/#{layer}"] = lt
+    lt
+  end
+
+  class Tachyon
+    attr_reader :lab, :position, :layer
+    def initialize(lab, position, layer=0)
+      @lab = lab
+      @position = position
+      @layer = layer
+    end
+
+    def count_lifetimes
+      if layer >= lab.layers.count
+        1
+      else
+        if at_splitter?
+          self.class.new(lab, position - 1, layer + 1).count_lifetimes + 
+            self.class.new(lab, position + 1, layer + 1).count_lifetimes
+        else
+          self.class.new(lab, position, layer + 1).count_lifetimes
+        end
+      end
+    end
+
+    def at_splitter?
+      lab.layers[layer].line[position] == "^"
+    end
+  end
+
+  class Layer
+    attr_reader :line
+    def initialize(line)
+      @line = line
+    end
+
+    def self.for(line)
+      new line.split("")
+    end
+
+    def blank_beams
+      Array.new(line.length, false)
+    end
+
+    def split_beams(input_beams)
+      split_count = 0
+      output = 0.upto(line.length - 1).map do |i|
+        if line[i] == "^"
+          split_count += 1 if input_beams[i]
+          false
+        elsif i > 0 && line[i - 1] == "^" && input_beams[i - 1]
+          true
+        elsif i < (line.length - 1) && line[i + 1] == "^" && input_beams[i + 1]
+          true
+        elsif line[i] == "S"
+          true
+        else
+          input_beams[i]
+        end
+      end
+      [output, split_count]
+    end
+  end
+end
diff --git a/ruby/2025/7/test/test_laboratories.rb b/ruby/2025/7/test/test_laboratories.rb
new file mode 100644
index 0000000..93a9cc7
--- /dev/null
+++ b/ruby/2025/7/test/test_laboratories.rb
@@ -0,0 +1,44 @@
+require "minitest/autorun"
+
+require "laboratories"
+
+class TestLaboratories < Minitest::Test
+  def test_split_count
+    lab = Laboratories.for <<-END
+.......S.......
+...............
+.......^.......
+...............
+......^.^......
+...............
+.....^.^.^.....
+...............
+....^.^...^....
+...............
+...^.^...^.^...
+...............
+..^...^.....^..
+...............
+.^.^.^.^.^...^.
+...............
+END
+    assert_equal(21, lab.split_count)
+  end
+end
+
+class TestLayer < Minitest::Test
+  def test_split_beams
+    layer = Laboratories::Layer.for(".S.")
+    assert_equal([[false, true, false], 0], layer.split_beams([false, false, false]))
+
+    layer = Laboratories::Layer.for("..")
+    assert_equal([[true, false], 0], layer.split_beams([true, false]))
+
+    layer = Laboratories::Layer.for(".^.")
+    assert_equal([[true, false, true], 1], layer.split_beams([false, true, false]))
+
+    layer = Laboratories::Layer.for("^.^")
+    assert_equal([[false, true, false], 0], layer.split_beams([false, true, false]))
+    assert_equal([[false, true, false], 2], layer.split_beams([true, false, true]))
+  end
+end