Advent of code, day 2

day2.rb

#!/usr/bin/env ruby

# Advent of code, day 2
# http://adventofcode.com/day/2

class Box

  def self.from_input(line)
    dims = line.split("x").map do |s|
      Integer(s)
    end
    new(dims)
  end

  def initialize(dims)
    @dims = dims
  end

  def area
    2 * side_areas.reduce(&:+)
  end

  def area_of_smallest_side
    side_areas.min
  end

  def wrapping_paper_area
    area + area_of_smallest_side
  end

  private

  def side_areas
    @dims.combination(2).map do |x, y|
      x * y
    end
  end
   
end

total_wrapping_paper_area = File.read("input").lines.map do |line|
  Box.from_input(line).wrapping_paper_area
end.reduce(&:+)
puts total_wrapping_paper_area

day_2_part_2.rb

#!/usr/bin/env ruby

# Advent of code, day 2
# http://adventofcode.com/day/2

class Box

  def self.from_input(line)
    dims = line.split("x").map do |s|
      Integer(s)
    end
    new(dims)
  end

  def initialize(dims)
    @dims = dims
  end

  def feet_of_ribbon
    smallest_perimeter + volume
  end

  def wrapping_paper_area
    area + area_of_smallest_side
  end

  private

  def area
    2 * side_areas.reduce(&:+)
  end

  def area_of_smallest_side
    side_areas.min
  end

  def volume
    @dims.reduce(&:*)
  end

  def smallest_perimeter
    perimeters.min
  end

  def side_areas
    @dims.combination(2).map do |x, y|
      x * y
    end
  end

  def perimeters
    @dims.combination(2).map do |x, y|
      2 * (x + y)
    end
  end
   
end

boxes = File.read("input").lines.map do |line|
  Box.from_input(line)
end
total_wrapping_paper_area = boxes.map(&:wrapping_paper_area).reduce(&:+)
total_feet_of_ribbon = boxes.map(&:feet_of_ribbon).reduce(&:+)
puts total_wrapping_paper_area
puts total_feet_of_ribbon