Advent of Code 2023 day001.rb

day001.rb

require_relative "main"

module Day001
  INPUT = File.read('INPUT.txt')

  lines = INPUT.to_lines

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

  values = lines.map do |line|
    digit_chars = line.gsub(/\D/, "").chars
    [digit_chars.first, digit_chars.last].join.to_i
  end

  answer1 = values.sum

  pp answer1

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

  # What are the first and last positions of all words in the string?
  get_positions = ->(words, string) do
    positions = []
    words.each.with_index do |word, i|
      index_first = string.index(word)
      if index_first
        index_last = string.rindex(word)
        positions.push([index_first, i])
        positions.push([index_last, i])
      end
    end
    positions
  end

  values = lines.map do |line|
    word_positions = get_positions.call(%w[zero one two three four five six seven eight nine], line)
    digit_positions = get_positions.call(%w[0 1 2 3 4 5 6 7 8 9], line)

    sorted_positions = (word_positions + digit_positions).sort_by(&:first)

    first_digit = sorted_positions.first.last
    last_digit = sorted_positions.last.last

    [first_digit, last_digit].join.to_i
  end

  answer2 = values.sum

  pp answer2

  #######################
  # Part 2, alternative #
  #######################

  total = 0
  lines.each do |line|
    first_position = nil
    first_value = nil

    last_position = nil
    last_value = nil

    needles = %w[zero one two three four five six seven eight nine 0 1 2 3 4 5 6 7 8 9]

    needles.each.with_index do |needle, index|
      i = 0
      j = 0
      while i <= line.length
        if j == needle.length
          if first_position.nil? || i - needle.length < first_position
            first_position = i - needle.length
            first_value = index % 10
          end
          if last_position.nil? || i - needle.length > last_position
            last_position = i - needle.length
            last_value = index % 10
          end
        end
        if line[i] == needle[j]
          j += 1
        elsif line[i] == needle[0]
          j = 1
        else
          j = 0
        end
        i += 1
      end
    end
    var = first_value * 10 + last_value
    total += var
  end

  answer2 = total

  pp answer2
end