Advent of Code, day 15

day15.rb

# http://adventofcode.com/day/15

require "forwardable"

Ingredient = Struct.new(:coefficients, :calories)

class Ingredients

  extend Forwardable

  def initialize
    @ingredients = []
  end

  def_delegators :@ingredients, :<<, :size

  def score(amounts)
    amounts.zip(@ingredients).map do |amount, ingredient|
      ingredient.coefficients.map do |coefficient|
        amount * coefficient
      end
    end.transpose.map do |a|
      a.reduce(&:+)
    end.map do |factor|
      [factor, 0].max
    end.reduce(&:*)
  end

  def calories(amounts)
    amounts.zip(@ingredients).map do |amount, ingredient|
      amount * ingredient.calories
    end.reduce(&:+)
  end
   
end

def digits_adding_up_to(num_digits:, sum:)
  f = ->(yielder, digits = []) do   
    if digits.size == num_digits - 1
      yielder.yield(digits + [sum - digits.reduce(0, &:+)])
    else
      digit_max = sum - digits.reduce(0, &:+)
      (1..(digit_max - 1)).each do |digit|
        f.(yielder, digits + [digit])
      end
    end
  end
  Enumerator.new { |yielder| f.(yielder) }
end

def amounts_enum
  digits_adding_up_to(num_digits: @ingredients.size, sum: 100)
end

def parse(file)
  ingredients = Ingredients.new
  file.each_line.each do |line|
    *coefficients, calories = line.scan(/-?\d+/).map do |s|
      Integer(s)
    end
    ingredients << Ingredient.new(coefficients, calories)
  end
  ingredients
end

@ingredients = File.open("input", "r") { |file| parse(file) }

# part 1
best_score = amounts_enum.map do |amounts|
  @ingredients.score(amounts)
end.max
puts best_score

# part 2
best_score = amounts_enum.select do |amounts|
  @ingredients.calories(amounts) == 500
end.map do |amounts|
  @ingredients.score(amounts)
end.max
puts best_score