Finology challenge: Sum of primes below 2 million and sum of consecutive prime below 1 million to be a prime.

prime_sum_with_consecutive_prime_sum.rb

'''
Problem 1
The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17
Find the sum of all the primes below 2 million.

Problem 2
Which prime, below one million, can be written as the sum of the
most consecutive primes?
'''

class GenerateSolution

  def sieve_of_eratosthenes(n)
    primes = (0..n).to_a
    primes[0] = primes[1] = nil
    primes.each do |p|
      next unless p
      break if p * p > n
      (p*p).step(n, p) { |m| primes[m] = nil }
    end
    primes.compact
  end

  def prime?(number)
    return false if (number <= 1)
    return true if (number <= 3)

    return false if (number % 2 == 0 || number % 3 == 0)

    i = 5
    while (i*i < number)
      return false if (number % i == 0 || number % (i+2) == 0)
      i += 6
    end

    return true
  end

  def consecutive_prime_sum(primes, max_range)
    max_sum = 0
    max_no_of_primes = 0
    for i in (0...primes.count)
      for j in (i...primes.count)
        sum, counter = primes[i..j].reduce(:+), j - i + 1
        break if sum > max_range
        if (prime?(sum)) && (max_no_of_primes < counter)
          max_sum = sum
          max_no_of_primes = counter
        end
      end
    end
    return max_sum
  end


end

test1_max_range = 2000000
test2_max_range = 1000000
solution = GenerateSolution.new

start = Time.now

primes = solution.sieve_of_eratosthenes(test1_max_range)
puts "Sum of primes below #{test1_max_range} = #{primes.reduce(:+)}"
puts "The prime number below #{test2_max_range}, can be written as the sum of the most consecutive primes = #{solution.consecutive_prime_sum(primes, test2_max_range)}"

finish = Time.now

puts "Program excecution time = #{finish - start}"