sum_of_primes.rb

# The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.

# Find the sum of all the primes below two million.

# Slow

def is_prime?(num)
  (2..Math.sqrt(num)).each { |i|
    if num % i == 0 && i < num
      return false
    end
  }
  true
end


def find_primes(num)
  primes = []
  num.times do |i|
    if is_prime?(i)
      primes << i
    end
  end
  primes
end

def sum_of_primes(num)
  primes = find_primes(num)
  sum = primes.reduce(:+)
  sum = sum - 1
end


p sum_of_primes(2_000_000)