[ruby]Sieve of Eratosthenes with Ruby

primes.rb

def primes(max)
  nums = Array.new(max + 1, 1)
  nums[0] = nums[1] = 0

  (2..Math.sqrt(max)).each do |sieve|
    if nums[sieve] == 1
      (2 * sieve).step(max, sieve).each do |num|
        nums[num] = 0
      end
    end
  end

  (2..max).select { |num| nums[num] == 1 }
end

puts primes(100)
#=> [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]

start = Time.now
primes(1_000_000)
puts Time.now - start
#=> 0.363797