Advent of Code 2024 day012.rb

day012.rb

require_relative "main"

module Day012
  INPUT = File.read("INPUT.txt")

  grid = INPUT.to_grid
  origins = grid.each_with_object(Hash.new { |h, k| h[k] = [] }) { |v, value, a| a[value].push(v) }

  answer1 = 0
  answer2 = 0

  grid.raw.flatten.uniq.each do |char|
    visited_global = Hash.new { |h, k| h[k] = false }

    origins[char].each do |origin|
      next if visited_global[origin]

      visited_local = Hash.new { |h, k| h[k] = false }
      corners = 0
      edges_to_remove = 0

      q = [origin]
      while q.count > 0
        c = q.shift

        corners += [
          [grid.get_value(c.north), grid.get_value(c.east)].none?(char),
          [grid.get_value(c.north), grid.get_value(c.west)].none?(char),
          [grid.get_value(c.south), grid.get_value(c.west)].none?(char),
          [grid.get_value(c.south), grid.get_value(c.east)].none?(char),
          [grid.get_value(c.north), grid.get_value(c.east)].all?(char) && grid.get_value(c.northeast) != char,
          [grid.get_value(c.north), grid.get_value(c.west)].all?(char) && grid.get_value(c.northwest) != char,
          [grid.get_value(c.south), grid.get_value(c.west)].all?(char) && grid.get_value(c.southwest) != char,
          [grid.get_value(c.south), grid.get_value(c.east)].all?(char) && grid.get_value(c.southeast) != char
        ].count(true)

        grid.four(c).filter { !visited_local[_1] && grid.get_value(_1) == char }.each do |n|
          q.push(n) unless q.include?(n)
          edges_to_remove += 1
        end
        visited_global[c] = visited_local[c] = true
      end

      area = visited_local.filter { _2 }.keys.count
      perimeter = area * 4 - edges_to_remove * 2
      sides = corners

      answer1 += perimeter * area
      answer2 += sides * area
    end
  end

  pp answer1

  pp answer2
end