Day 19 - Puzzle 2

lib/solutions/day_19.rb

@@ -5,7 +5,36 @@ def part_one(input)
   end
 
   def part_two(input)
-    0
+    sim = DayTwo.new(input)
+    sim.run!
+  end
+
+  class DayTwo
+    def initialize(input)
+      lines = input.split("\n")
+      @towels = lines[0].split(",").map(&:strip)
+      @patterns = lines[2..-1]
+    end
+
+    def possible?(pattern)
+      possibles = Array.new(pattern.size + 1, 0)
+      possibles[0] = 1
+
+      (0...pattern.size).each do |i|
+        next if possibles[i] == 0
+        @towels.each do |towel|
+          if pattern[i..-1].start_with?(towel)
+            possibles[i + towel.size] += possibles[i]
+          end
+        end
+      end
+
+      possibles[pattern.size]
+    end
+
+    def run!
+      @patterns.reduce(0) { |count, pattern| count += possible?(pattern) }
+    end
   end
 
   class DayOne

spec/solutions/day_19_spec.rb

@@ -12,7 +12,7 @@
 
   describe '#part_two' do
     it 'calculates the correct solutions for part two' do
-      expect(subject.part_two(input)).to eq(0)
+      expect(subject.part_two(input)).to eq(16)
     end
   end
 end