Advent of Code 2023 day005.rb

day005.rb

require_relative "main"

module Day005
  INPUT = File.read('INPUT.txt')

  lines = INPUT.to_lines

  seeds = lines.shift.split(":").last.split_strip(" ").map(&:to_i)
  lines.shift

  categories = []
  lines.each do |line|
    matches = /([a-z]+)-to-([a-z]+)/.match(line)
    if matches
      categories.push([])
    elsif line != ""
      parts = line.split_strip(" ").map(&:to_i)
      dest_start = parts[0]
      source_start = parts[1]
      size = parts[2]
      dest_end = dest_start + size - 1
      source_end = source_start + size - 1

      categories.last.push({
        source: (source_start..source_end),
        dest: (dest_start..dest_end)
      })
    end
  end

  seed_to_location = ->(seed) do
    cursor = seed
    categories.each do |category|
      found = false
      category.each do |map|
        if map[:source].include?(cursor)
          found = true
          source_i = cursor - map[:source].first
          dest_v = map[:dest].first + source_i
          cursor = dest_v
        end
        break if found
      end
    end
    cursor
  end

  location_to_seed = ->(location) do
    cursor = location
    categories.reverse.each do |category|
      found = false
      category.each do |map|
        if map[:dest].include?(cursor)
          found = true
          dest_i = cursor - map[:dest].first
          source_v = map[:source].first + dest_i
          cursor = source_v
        end
        break if found
      end
    end
    cursor
  end

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

  min1 = nil
  seeds.each do |seed|
    cursor = seed_to_location.call(seed)
    min1 = cursor if min1.nil? || cursor < min1
  end
  answer1 = min1

  pp answer1

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

  seed_ranges = seeds.each_slice(2).map do |pair|
    first = pair[0]
    last = pair[0] + pair[1]
    (first..last)
  end

  # Let's try 100,000 values, spaced 100 apart
  min2 = nil
  100000.times do |i|
    j = i * 100
    seed = location_to_seed.call(j)
    break_all = false
    seed_ranges.filter.with_index do |range|
      if range.include?(seed)
        k = j
        loop do
          seed2 = location_to_seed.call(k)
          if range.include?(seed2)
            min2 = k if min2.nil? || k < min2
          else
            break_all = true
            break
          end
          k -= 1
        end
      end

      break if break_all
    end

    break if break_all
  end

  answer2 = min2

  pp answer2
end