project_euler_8.rb

large_num = 7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450

class ProductEvaluator

  def initialize(large_num)
    @large_num_array = large_num.to_s.split(//)
    @product_array = []
    evaluate_five_numbers_at_a_time
  end

  def evaluate_five_numbers_at_a_time
    while @large_num_array.length >= 5
      add_five_numbers_in_sequence_to_array_and_remove_first
    end
  end

  def add_five_numbers_in_sequence_to_array_and_remove_first
    @product_array << eval(@large_num_array.take(5).join("*"))
    @large_num_array.shift
  end

  def find_the_largest_number_in_the_product_array
    @product_array.max
  end

end

p ProductEvaluator.new(large_num).find_the_largest_number_in_the_product_array #=> 40824