# all rotations are clockwise # all flips are vertical class Tile attr_reader :id, :raw def initialize(id, raw) @id, @raw = id, raw end def [](y, x) @raw.fetch(y).fetch(x) end def edge_keys { top: @raw.first, down: @raw.last, left: @raw.transpose.first, right: @raw.transpose.last, }.transform_values(&:join) end def permutations (0..3).map {|i| i.times.inject(self) {|x,_| x.rotated } }.flat_map {|x| [x, x.flipped] } end def rotated self.class.new(@id, @raw.reverse.transpose) end def flipped self.class.new(@id, @raw.reverse) end def to_s @raw.map(&:join).join("\n") end end Edge = Struct.new(*%i[ key from to rotations is_mirrored ]) do def mirrored? is_mirrored end end tiles = ARGF.read .scan(/Tile (\d+):\n((?:[.#]+\n)+)/m) .to_h .transform_values {|v| v.split("\n").map {|row| row.chars } } .map {|k,v| [k, Tile.new(k, v)] } .to_h keys_to_tiles = Hash.new {|h,k| h[k] = [] } tiles.values.each do |tile| tile.edge_keys.values.each do |key| keys_to_tiles[key] << tile.id keys_to_tiles[key.reverse] << tile.id end end start_corner = tiles.values.find {|tile| tile.edge_keys.values_at(:left, :top).all? {|key| keys_to_tiles.fetch(key).size == 1 } } image = [[start_corner]] until image.map(&:size).sum == tiles.size current = image.last.last right_key = current.edge_keys.fetch(:right) if right_id = keys_to_tiles.fetch(right_key, nil).find {|id| id != current.id } right_tile = tiles.fetch(right_id).permutations.find {|p| p.edge_keys.fetch(:left) == right_key } image.last << right_tile else current = image.last.first down_key = current.edge_keys.fetch(:down) break unless down_id = keys_to_tiles.fetch(down_key).find {|id| id != current.id } down_tile = tiles.fetch(down_id).permutations.find {|p| p.edge_keys.fetch(:top) == down_key } image << [down_tile] end end full_raw = image.map {|row| row.map {|tile| tile.raw[1..-2].map {|row| row[1..-2] } }}.flat_map {|row| row.inject(&:zip).map(&:flatten) } full_tile = Tile.new(nil, full_raw) sea_monster = <<~SEA_MONSTER.split("\n").map(&:chars) # # ## ## ### # # # # # # SEA_MONSTER needle = sea_monster.flat_map.with_index {|row,y| row.filter_map.with_index {|c,x| c == ?# ? [y,x] : nil } } num_monsters = full_tile.permutations.map {|tile| needle_maxes = needle.transpose.map(&:max) haystack = (0...tile.raw.size-needle_maxes.first).flat_map {|y| (0...tile.raw.first.size-needle_maxes.last).map {|x| [y, x] } } haystack.count {|y,x| needle.all? {|dy,dx| tile[y+dy, x+dx] == ?# } } }.sum puts full_tile.raw.map {|row| row.count(?#) }.sum - (num_monsters * needle.size)