Solution for Day 20

day_20/both.rb

@@ -0,0 +1,227 @@
+# frozen_string_literal: true
+
+require 'pry'
+
+# @type [Hash]
+input = File.read('./input').split("\n\n").map do |tile|
+  tile = tile.split("\n")
+  id = tile.shift.scan(/\d+/).first.to_i
+  Hash[id, tile]
+end.inject :merge
+
+# @type [Array]
+$corners = []
+
+def build_combinations(tile)
+  top = tile.first
+  rev_top = top.reverse
+  btm = tile.last
+  rev_btm = btm.reverse
+  left = tile.map { |a| a[0] }.join
+  rev_left = left.reverse
+  right = tile.map { |a| a[-1] }.join
+  rev_right = right.reverse
+  [left, rev_left, right, rev_right, top, rev_top, btm, rev_btm]
+end
+
+def get_sides(tile)
+  top = tile.first
+  btm = tile.last
+  left = tile.map { |a| a[0] }
+  right = tile.map { |a| a[-1] }
+  [top, btm, left, right]
+end
+
+def check_tile(tile, input)
+  tile_id = tile.first
+  combs = build_combinations(tile.last)
+
+  t = input.map do |id, val|
+    next if tile_id == id
+
+    (combs & build_combinations(val)).count
+  end
+end
+
+input.each do |tile|
+  $corners << tile.first if check_tile(tile, input).count(2) == 2
+end
+
+class Tile
+  attr_accessor :id, :grid
+  def initialize(id, grid)
+    @id = id
+    @grid = grid
+  end
+
+  def top
+    @grid.first.join
+  end
+
+  def btm
+    @grid.last.join
+  end
+
+  def left
+    @grid.map(&:first).join
+  end
+
+  def right
+    @grid.map(&:last).join
+  end
+
+  def grid_without_borders
+    out = []
+    @grid.each_with_index do |line, i|
+      next if i == 0
+      next if i == 9
+
+      out << line[1..-2]
+    end
+    out
+  end
+
+  def edges
+    [top, right, btm, left]
+  end
+
+  def edge_orientations
+    out = [*edges]
+    out.push(*edges.map(&:reverse))
+    out
+  end
+
+  def flip_vertical
+    self.class.new @id, @grid.map(&:reverse)
+  end
+
+  def flip_horizontal
+    self.class.new @id, @grid.reverse
+  end
+
+  def rotate
+    self.class.new @id, @grid.transpose.map(&:reverse)
+  end
+
+  def all_rotations
+    out = [self]
+    3.times do
+      out << out.last.rotate
+    end
+    out
+  end
+
+  def all_orientations
+    out = [self, flip_horizontal, flip_vertical, flip_horizontal.flip_vertical]
+    out.dup.each do |tile|
+      out.push(*tile.all_rotations)
+    end
+    out.uniq
+  end
+
+  def to_s
+    @grid.map(&:join).join "\n"
+  end
+
+  def find_matching_right_from(tiles)
+    tiles.map(&:all_orientations).flatten.uniq.each do |ori|
+      return ori if right == ori.left
+    end
+  end
+
+  def find_matching_bottom_from(tiles)
+    tiles.map(&:all_orientations).flatten.uniq.each do |ori|
+      return ori if btm == ori.top
+    end
+  end
+
+  def find_monsters
+    count = 0
+    image = to_s.lines.map(&:chomp)
+    image[0..-3].each_with_index do |row, y|
+      row[0..-20].chars.each_index do |x|
+        count += 1 if monster_at?(x, y, image)
+      end
+    end
+    count
+  end
+
+  def monster_at?(x, y, image)
+    MONSTER.each_with_index do |regex, i|
+      return false unless image[y + i][x, 20][regex]
+    end
+    true
+  end
+end
+
+def rotate_top_left(tl)
+  tl.all_orientations.each do |ori|
+    left_side = ori.left
+    top_side = ori.top
+
+    unless $all_orientations.include?(left_side) || $all_orientations.include?(top_side)
+      return ori
+    end
+  end
+  nil
+end
+
+# @type [Array]
+$tiles = input.map do |id, grid|
+  Tile.new id, grid.map(&:chars)
+end
+
+top_left = $tiles.find { |tile| tile.id == $corners.first }
+$tiles.delete(top_left)
+$all_orientations = $tiles.map(&:edge_orientations).flatten.uniq
+
+$map = [[]]
+$map[0] << rotate_top_left(top_left)
+
+11.times do
+  $map[0] << $map[0].last.find_matching_right_from($tiles)
+  $tiles.delete($tiles.find { |t| t.id == $map[0].last.id })
+  $map << [$map.last.first.find_matching_bottom_from($tiles)]
+  $tiles.delete($tiles.find { |t| t.id == $map.last.last.id })
+end
+
+(1..11).each do |y|
+  11.times do
+    $map[y] << $map[y].last.find_matching_right_from($tiles)
+    $tiles.delete($tiles.find { |t| t.id == $map[y].last.id })
+  end
+end
+
+corners = [$map[0][0].id, $map[0][11].id, $map[11][0].id, $map[11][11].id]
+puts "Corners: #{$corners.inspect}"
+puts "Product of corner ids: #{corners.inject(:*)}"
+MONSTER = [
+  /..................#./,
+  /#....##....##....###/,
+  /.#..#..#..#..#..#.../
+].freeze
+image = ''
+
+$map.each do |row|
+  out = Array.new(8) { '' }
+  row.each do |tile|
+    tile.grid_without_borders.each_with_index do |line, i|
+      out[i] += line.join
+    end
+  end
+  image += out.join "\n"
+  image += "\n"
+end
+
+image = image.lines.map(&:chomp)
+image = Tile.new 1, image.map(&:chars)
+
+monsters = 0
+image.all_orientations.each do |ori|
+  monsters = ori.find_monsters
+
+  break if monsters > 0
+end
+
+puts "Monsters: #{monsters}"
+puts "Num of '#' not belonging to monster: #{image.to_s.count('#') - 15 * monsters}"