day 10, part 2

Copied more from Bill so I could move on with my life. Thanks, Bill.

Author: Robb Kidd

2023/ruby/day10.rb

@@ -10,14 +10,25 @@ class Day10 < Day # >
   #   day = Day10.new(MORE_COMPLEX_INPUT)
   #   day.part1 #=> 8
   def part1
-    pipe_maze = PipeMaze.new(input)
-    # puts pipe_maze.to_ugly_sweater
-    pipe_maze.loop_path.length / 2
+    @pipe_maze = PipeMaze.new(input)
+    @pipe_maze.loop_path.length / 2
   end
 
   # @example
-  # day.part2 #=> 'how are you'
+  #   day = Day10.new(PART2_INPUT)
+  #   day.part1
+  #   day.part2 #=> 4
+  # @example larger example
+  #   day = Day10.new(PART2_LARGER_EXAMPLE)
+  #   day.part1
+  #   day.part2 #=> 8
+  # @example junk example
+  #   day = Day10.new(PART2_JUNK_EXAMPLE)
+  #   day.part1
+  #   day.part2 #=> 10
   def part2
+    puts @pipe_maze.to_ugly_sweater
+    @pipe_maze.inner_cells.length
   end
 
   EXAMPLE_INPUT = <<~INPUT
@@ -28,13 +39,51 @@ def part2
     .....
   INPUT
 
-  MORE_COMPLEX_INPUT= <<~INPUT
+  MORE_COMPLEX_INPUT = <<~INPUT
     ..F7.
     .FJ|.
     SJ.L7
     |F--J
     LJ...
   INPUT
+
+  PART2_INPUT = <<~INPUT
+    ...........
+    .S-------7.
+    .|F-----7|.
+    .||.....||.
+    .||.....||.
+    .|L-7.F-J|.
+    .|..|.|..|.
+    .L--J.L--J.
+    ...........
+  INPUT
+
+  PART2_LARGER_EXAMPLE = <<~INPUT
+    .F----7F7F7F7F-7....
+    .|F--7||||||||FJ....
+    .||.FJ||||||||L7....
+    FJL7L7LJLJ||LJ.L-7..
+    L--J.L7...LJS7F-7L7.
+    ....F-J..F7FJ|L7L7L7
+    ....L7.F7||L7|.L7L7|
+    .....|FJLJ|FJ|F7|.LJ
+    ....FJL-7.||.||||...
+    ....L---J.LJ.LJLJ...
+  INPUT
+
+  PART2_JUNK_EXAMPLE = <<~INPUT
+    FF7FSF7F7F7F7F7F---7
+    L|LJ||||||||||||F--J
+    FL-7LJLJ||||||LJL-77
+    F--JF--7||LJLJ7F7FJ-
+    L---JF-JLJ.||-FJLJJ7
+    |F|F-JF---7F7-L7L|7|
+    |FFJF7L7F-JF7|JL---7
+    7-L-JL7||F7|L7F-7F7|
+    L.L7LFJ|||||FJL7||LJ
+    L7JLJL-JLJLJL--JLJ.L
+  INPUT
 end
 
 class PipeMaze
@@ -91,6 +140,27 @@ def step_from(coords, direction)
     ]
   end
 
+  def inner_cells
+    @inner_cells ||= find_inner_cells
+  end
+
+  # Very much copied from Bill Mill's hack; works for junk and real input, but off-by-one for others.
+  def find_inner_cells
+    innercells = []
+    @grid.row_bounds.map do |row|
+      bars = 0
+      @grid.column_bounds.map do |column|
+        on_the_loop = loop_path.include?([row,column])
+        if on_the_loop && ["│", "└", "┘", "╳"].include?(at([row, column]))
+            bars += 1
+        elsif bars % 2 == 1 && !on_the_loop
+            innercells << [row,column]
+        end
+      end
+    end
+    return innercells
+  end
+
   def at(coords)
       @grid.at(coords)
   end
@@ -112,7 +182,6 @@ def towards(from_coords, direction)
 
   # [step travel direction, pipe type] => next step travel direction
   PIPE_FLOWS = {
-    # "│─└┘┐┌░╳"
     # | is a vertical pipe connecting north and south.
     [:north, "│"] => :north,
     [:south, "│"] => :south,
@@ -145,9 +214,12 @@ def towards(from_coords, direction)
   }
 
   def to_ugly_sweater
+    "\n" +
     @grid.to_s { |coords, value|
       if loop_path.include?(coords)
         value.make_it_red
+      elsif inner_cells.include?(coords)
+        "I".make_it_green.make_it_bold
       else
         value.make_it_green
       end