gistfile1.rb

scans = [
  ['A','B','C','D','A','B','A','A'],
  ['C','C','C','C','C','C','C'],
  ['A','B','C','D']
]

products = [
  { :code => 'A', :volume => 4, :price => 7 },
  { :code => 'A', :volume => 1, :price => 2 },
  { :code => 'B', :volume => 1, :price => 12 },
  { :code => 'C', :volume => 6, :price => 6 },
  { :code => 'C', :volume => 1, :price => 1.25 },
  { :code => 'D', :volume => 1, :price => 0.15 }
]

unique_products = products.uniq { |x| x[:code] }

scans.each do |scan|
  puts scan.inspect
  value = 0

  unique_products.each do |product|
    code = product[:code]
    scan_num = scan.select { |x| x == code }.count

    volume_discount = products.select { |x| x[:code] == code && x[:volume] > 1 }
    if !volume_discount.empty?
      volume = volume_discount.first[:volume]
      price  = volume_discount.first[:price]

      volume_num = scan_num / volume
      remainder  = scan_num % volume

      value += volume_num * price
    end

    remainder ||= scan_num

    price = products.select { |x| x[:code] == code && x[:volume] == 1 }.first[:price]
    value += remainder * price
  end

  puts value
end