2025 ruby day 4

ruby/2025/4/bin/problem

@@ -0,0 +1,7 @@
+#!/usr/bin/env ruby
+require "printing_department"
+
+printing_department = PrintingDepartment.for STDIN.read.chomp
+puts "Part 1: #{printing_department.accessible_rolls.count}"
+printing_department.remove_all_accessible_rolls!
+puts "Part 2: #{printing_department.removed_rolls.count}"

ruby/2025/4/lib/printing_department.rb

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+class PrintingDepartment
+  attr_reader :rows, :removed_rolls
+  def initialize(rows)
+    @rows = rows
+    @removed_rolls = []
+  end
+
+  def self.for(string)
+    new string.split("\n").map{ |row| row.split("") }
+  end
+
+  def rolls
+    rows.each_with_index.map do |row, row_index|
+      row.each_with_index.map do |char, column_index|
+        [row_index, column_index] if char == "@"
+      end.compact
+    end.flatten(1)
+  end
+
+  def char_at(row, column)
+    rows[row][column]
+  end
+
+  def width
+    rows[0].length
+  end
+
+  def height
+    rows.length
+  end
+
+  def neighbor_indices(row, column)
+    [0, row - 1].max.upto([width - 1, row + 1].min).map do |r|
+      [0, column - 1].max.upto([height - 1, column + 1].min).map do |c|
+        [r, c]
+      end
+    end.flatten(1).reject{ |r, c| r == row && c == column }
+  end
+
+  def neighbors(row, column)
+    neighbor_indices(row, column).map { |nr, nc| char_at nr, nc }
+  end
+
+  def adjacent_roll_count(row, column)
+    neighbors(row, column).select { |char| char == "@" }.count
+  end
+
+  def accessible_rolls
+    rolls.select{ |r, c| adjacent_roll_count(r, c) < 4 }
+  end
+
+  def remove_roll!(row, col)
+    removed_rolls << [row, col]
+    rows[row][col] = "."
+  end
+
+  def remove_accessible_rolls!
+    accessible_rolls.each { |r, c| remove_roll! r, c }
+  end
+
+  def remove_all_accessible_rolls!
+    remove_accessible_rolls! until accessible_rolls.empty?
+  end
+end

ruby/2025/4/test/test_printing_department.rb

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+require "minitest/autorun"
+require "printing_department"
+
+class TestPrintingDepartment < Minitest::Test
+  def test_accessible_rolls
+    map = <<END
+..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.
+END
+
+    accessible_rolls_map = <<END
+..xx.xx@x.
+x@@.@.@.@@
+@@@@@.x.@@
+@.@@@@..@.
+x@.@@@@.@x
+.@@@@@@@.@
+.@.@.@.@@@
+x.@@@.@@@@
+.@@@@@@@@.
+x.x.@@@.x.
+END
+
+    printing_department = PrintingDepartment.for map
+    assert_equal(13, printing_department.accessible_rolls.count)
+    printing_department.remove_accessible_rolls!
+    assert_equal(12, printing_department.accessible_rolls.count)
+    printing_department.remove_all_accessible_rolls!
+    assert_equal(0, printing_department.accessible_rolls.count)
+    assert_equal(43, printing_department.removed_rolls.count)
+  end
+end