day 12, part 2 ... kinda

example input passes, but hnnnnnn it's slow:

Day12#part2#test_0001_ = 1.65 s = .

Does not fly for real input.

Author: Robb Kidd

2023/ruby/day12.rb

@@ -16,9 +16,17 @@ def part1
       .reduce(&:+)
   end
 
-  # example
-  # #day.part2 #=> 'how are you'
+  # @example
+  #   day.part2 #=> 525152
   def part2
+    @hot_springs ||= HotSprings.new(input)
+
+    @hot_springs
+      .unfold
+      .map { |even_more_springs, even_more_damaged_counts|
+        @hot_springs.scan(even_more_springs, even_more_damaged_counts)
+      }
+      .reduce(&:+)
   end
 
   EXAMPLE_INPUT = <<~INPUT
@@ -48,6 +56,20 @@ def initialize(input="")
         }
   end
 
+  # @example super simple
+  #   new(".# 1").unfold #=> [ [".#?.#?.#?.#?.#", [1,1,1,1,1]] ]
+  # @example 1st row
+  #   new("???.### 1,1,3").unfold #=> [ ["???.###????.###????.###????.###????.###", [1,1,3,1,1,3,1,1,3,1,1,3,1,1,3]] ]
+  def unfold
+    rows
+      .map { |springs, damaged_counts|
+        [
+          ([springs] * 5).join("?"),
+          damaged_counts * 5,
+        ]
+      }
+  end
+
   WORKING = "."
   DAMAGED = "#"
   UNKNOWN = "?"