Day twenty-three

23/main.rb

@@ -0,0 +1,78 @@
+#!/usr/bin/env ruby
+
+input = (ARGV.first.nil? ? DATA : ARGF)
+  .readlines(chomp: true)
+  .map { _1.split("-") }
+
+connections = Hash.new { _1[_2] = Set.new }
+
+input.each do |connection|
+  a, b = connection.sort
+
+  connections[a] << b
+  connections[b] << a
+end
+
+parties = Set.new
+connections.dup.each do |(node, neighbors)|
+  neighbors.each do |neighbor|
+    connections[neighbor].each do |neighbors_neighbor|
+      if neighbors.include?(neighbors_neighbor)
+        parties << [node, neighbor, neighbors_neighbor].sort
+      end
+    end
+  end
+end
+
+p parties.select { |party| party.any? { _1.match?(/^t/) } }.size
+
+largest = []
+connections.keys.each do |node|
+  (connections[node].size + 1).downto(1) do |size|
+    (connections[node] + [node]).to_a.combination(size) do |group|
+      if group.all? { |a| group.all? { |b| a == b || connections[a].include?(b) } }
+        if largest.size < group.size
+          largest = group
+          break
+        end
+      end
+    end
+    break if largest.size == size
+  end
+end
+
+p largest.sort.join(",")
+
+__END__
+kh-tc
+qp-kh
+de-cg
+ka-co
+yn-aq
+qp-ub
+cg-tb
+vc-aq
+tb-ka
+wh-tc
+yn-cg
+kh-ub
+ta-co
+de-co
+tc-td
+tb-wq
+wh-td
+ta-ka
+td-qp
+aq-cg
+wq-ub
+ub-vc
+de-ta
+wq-aq
+wq-vc
+wh-yn
+ka-de
+kh-ta
+co-tc
+wh-qp
+tb-vc
+td-yn