Advent of Code 2023 day006.rb

day006.rb

require_relative "main"

module Day006
  INPUT = File.read('INPUT.txt')

  lines = INPUT.to_lines

  ts = lines.shift.split_strip(":").last.split_strip(" ").map(&:to_i)
  ds = lines.shift.split_strip(":").last.split_strip(" ").map(&:to_i)

  data = ts.zip(ds)

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

  ways = Array.new(data.count, 0)
  data.each.with_index do |(t, d), j|
    t.times.each do |i|
      ways[j] += 1 if i * (t - i) > d
    end
  end

  answer1 = ways.arith_prod

  pp answer1

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

  t2 = data.map(&:first).join.to_i
  d2 = data.map(&:last).join.to_i

  i = 0
  j = t2 / 2
  k = nil
  while j - i > 1
    k = (j - i) / 2 + i

    (k * (t2 - k) > d2) ? j = k : i = k
  end

  min_t = (k * t2 <= d2) ? k + 1 : k

  answer2 = t2 - ((min_t - 1) + min_t)

  pp answer2
end