day 11, part 1

Horray for having a grid implementation already.

Author: Robb Kidd

2023/ruby/day11.rb

@@ -0,0 +1,115 @@
+require_relative 'day'
+require_relative 'grid'
+
+class Day11 < Day # >
+
+  # @example
+  #   day.part1 #=> 374
+  def part1
+    expanded_universe =
+      Grid.new(
+        expand_cosmically(
+          scan(input)
+        )
+      )
+
+    galaxies = []
+    expanded_universe.parse do |coords, value|
+      galaxies << coords if value == GALAXY
+    end
+
+    galaxies
+      .combination(2)
+      .map { |here, there| expanded_universe.manhattan_distance(here, there) }
+      .reduce(&:+)
+  end
+
+  # @example
+  # day.part2 #=> 'how are you'
+  def part2
+  end
+
+
+  # @example
+  #   simple_input = "...\n.#.\n...\n"
+  #   day.scan(simple_input) #=> [[".",".","."],[".","#","."],[".",".","."]]
+  def scan(image)
+    image
+      .split("\n")
+      .map(&:chars)
+  end
+
+  EMPTY_SPACE = '.'
+  GALAXY = '#'
+
+  # @example
+  #  scanned_image = day.scan(EXAMPLE_INPUT)
+  #  input_expanded = day.expand_cosmically(scanned_image)
+  #  input_expanded #=> day.scan(EXPANDED_INPUT)
+  def expand_cosmically(scanned_image)
+    # dupe empty-space rows
+    expanded_rows = []
+    scanned_image
+      .each do |row|
+        n = row.all?(EMPTY_SPACE) ? 2 : 1
+        n.times { expanded_rows << row }
+      end
+
+    # pivot the table, dupe empty-space columns
+    expanded_columns = []
+    expanded_rows
+      .transpose
+      .each do |column|
+        n = column.all?(EMPTY_SPACE) ? 2 : 1
+        n.times { expanded_columns << column }
+      end
+
+    # pivot things back around to original orientation
+    # unnecessary for computing distances, but wanted for
+    # visualizing output
+    3.times { expanded_columns = expanded_columns.transpose }
+    expanded_columns
+  end
+
+  # @example simple input
+  #   simple_input = "...\n.#.\n...\n"
+  #   scanned_image = day.scan(simple_input)
+  #   scanned_image #=> [[".",".","."],[".","#","."],[".",".","."]]
+  #   day.display(scanned_image) #=> simple_input
+  # @example example input
+  #   scanned_image = day.scan(EXAMPLE_INPUT)
+  #   day.display(scanned_image) #=> EXAMPLE_INPUT
+  def display(scanned_image)
+    scanned_image
+      .map { |row| row.join('') }
+      .join("\n") + "\n"
+  end
+
+  EXAMPLE_INPUT = <<~INPUT
+    ...#......
+    .......#..
+    #.........
+    ..........
+    ......#...
+    .#........
+    .........#
+    ..........
+    .......#..
+    #...#.....
+  INPUT
+
+  EXPANDED_INPUT = <<~INPUT
+    ....#........
+    .........#...
+    #............
+    .............
+    .............
+    ........#....
+    .#...........
+    ............#
+    .............
+    .............
+    .........#...
+    #....#.......
+  INPUT
+end

2023/ruby/grid.rb

@@ -170,9 +170,19 @@ def path_to_direction_map(path)
   # @example
   #
   def parse
-    @input
-      .split("\n")
-      .map { |line| line.chars }
+    split_input =
+      case @input
+      when Array # assume the lines and chars have been split already
+        @input
+      when String
+        @input
+          .split("\n")
+          .map { |line| line.chars }
+      else
+        raise("don't know how to parse #{input.inspect}")
+      end
+
+    split_input
       .each_with_index do |row, r|
         row.each_with_index do |char, c|
           @the_grid[[r, c]] = char