Advent of Code 2023 day010.rb

day010.rb

require_relative "main"

module Day010
  INPUT = File.read('INPUT.txt')

  grid = INPUT.to_grid

  GUIDES = {
    "7" => { V.northward => V.westward, V.eastward => V.southward },
    "F" => { V.westward => V.southward, V.northward => V.eastward },
    "L" => { V.southward => V.eastward, V.westward => V.northward },
    "J" => { V.eastward => V.northward, V.southward => V.westward },
    "-" => { V.eastward => V.eastward, V.westward => V.westward },
    "|" => { V.southward => V.southward, V.northward => V.northward }
  }

  ##########
  # Part 1 #
  ##########

  start = grid.find("S")

  cursor = nil
  start.four.each.with_index do |v, i|
    value = grid.get_value(v)

    if [
      i == 0 && ["7", "J", "-"].include?(value),
      i == 1 && ["7", "F", "|"].include?(value),
      i == 2 && ["F", "L", "-"].include?(value),
      i == 3 && ["L", "J", "|"].include?(value),
    ].any?
      cursor = v
      break
    end

  end

  raise 'wat' if cursor.nil?

  last_cursor = start
  corners = []
  cursors = []

  i = 0
  loop do
    cursors.push(cursor)
    value = grid.get_value(cursor)
    break if value == "S" && i > 0

    if ["7", "F", "L", "J"].include?(value)
      corners.push(cursor)
    end

    ingress = cursor - last_cursor
    egress = GUIDES[value][ingress]
    last_cursor = cursor
    cursor = egress + cursor

    i += 1
  end

  answer1 = (i + 1) / 2

  pp answer1

  ##########
  # Part 2 #
  ##########

  corners.unshift(start)

  poly = Polygon.new(*corners)

  c = grid.reduce(0) do |memo, v, _value|
    memo + ((!cursors.include?(v) && poly.contains_point?(v)) ? 1 : 0)
  end

  answer2 = c

  pp answer2
end