Advent of Code, day 17

day17.rb

#!/usr/bin/env ruby

# http://adventofcode.com/day/17

def containers_totalling(containers, target_sum)
  Enumerator.new do |yielder|
    (0...(2 ** containers.size)).map do |mask|
      selected_containers = containers.select.with_index do |container, bitnum|
        (mask & (1 << bitnum)) != 0
      end
      sum = selected_containers.reduce(0, &:+)
      yielder.yield(selected_containers) if sum == target_sum
    end
  end
end

def num_containers_totalling(containers, target_sum)
  containers_totalling(containers, target_sum).count
end

def min_containers_totalling(containers, target_sum)
  containers_totalling(containers, target_sum).map(&:size).min
end

containers = File.readlines("input").map(&:to_i)
target_sum = 150

# part 1
puts num_containers_totalling(containers, target_sum)

# part 2
num_containers = min_containers_totalling(containers, target_sum)
count = containers_totalling(containers, target_sum).count do |containers|
  containers.size == num_containers
end
puts count