--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/day12.rb	Sat Dec 16 20:04:27 2023 +0000
@@ -0,0 +1,83 @@
+#! /usr/bin/env ruby
+
+if ARGV.length != 1
+        abort("Incorrect arguments - needs input file")
+elsif not File.exist? (ARGV[0])
+	abort("File #{ARGV[0]} did not exist")
+end
+
+file = ARGV[0]
+
+def truthy?(val)
+	!val.nil? and val != [] and val != ""
+end
+
+def arrangements(candidate, other_candidates, run_lengths, cache)
+#	puts "Looking for #{run_lengths} (#{truthy?(run_lengths)}) in #{candidate} (#{truthy?(candidate)}), #{other_candidates.nil? '' : other_candidates.join(", ")}"
+	puts "Looking for #{run_lengths} in #{candidate}, #{other_candidates.nil? ? '' : other_candidates.join(",")}"
+	if !truthy?(candidate) and !truthy?(run_lengths)
+		puts "Combos: 1 (both empty)"
+		return 1
+	elsif !truthy?(run_lengths) and !candidate.include? "#" and (!truthy?(other_candidates) or other_candidates.all? {|candidate| truthy?(candidate)})
+		return 1
+	elsif (!truthy?(candidate) and truthy?(run_lengths)) or (!truthy?(run_lengths) and candidate.include? "#")
+		puts "Combos: 0 (fail)"
+		return 0
+	end
+	find_length = run_lengths.first
+
+	cached = cache[[candidate, other_candidates, run_lengths]]
+	if !cached.nil?
+		puts "Combos: #{cached} (cached)"
+		return cached
+	end
+		
+	
+	combo_count = 0
+
+	if find_length == candidate.length
+		# We found a perfect match!
+		new_candidate = other_candidates[0]
+		new_other_candidates = other_candidates[1..]
+		combo_count += arrangements(new_candidate, new_other_candidates, run_lengths[1..], cache)
+		if truthy?(candidate) and !candidate.include? "#"
+			# What if we skip this all all question mark candidate and try later?
+			combo_count += arrangements(new_candidate, new_other_candidates, run_lengths, cache)
+		end
+	elsif find_length < candidate.length
+		if candidate[find_length] != "#"
+			if find_length == candidate.length - 1
+				new_candidate = other_candidates[0]
+				new_other_candidates = other_candidates[1..]
+			else
+				new_candidate = candidate[(find_length+1)..]
+				new_other_candidates = other_candidates
+			end
+			# We found a substring match that ends in a valid place
+			combo_count += arrangements(new_candidate, new_other_candidates, run_lengths[1..], cache)
+		end
+		if candidate[0] == "?"
+			# We've got space, so try the other combo
+			combo_count += arrangements(candidate[1..], other_candidates, run_lengths, cache)
+		end
+	else
+		# This candidate must all be good parts
+		combo_count += arrangements(other_candidates[0], other_candidates[1..], run_lengths, cache)
+	end
+	puts "Combos: #{combo_count}\n"
+	cache[[candidate, other_candidates, run_lengths]] = combo_count
+	combo_count
+end
+
+cache = Hash.new
+
+combos = File.open(file, "r").each_line(chomp: true).map do |line|
+        symbols, run_lengths_str = line.split(" ")
+        run_lengths = run_lengths_str.split(",").map(&:to_i)
+        candidates = symbols.split(".").filter {|candidate| candidate != ""}
+	candidate = candidates.shift
+	line_arrangements = arrangements(candidate, candidates, run_lengths, cache)
+	puts "Line arrangements: #{line_arrangements}\n\n"
+	line_arrangements
+end
+puts "#{combos} = #{combos.sum}"