Project Euler 35: Ruby

In my attempt to learn Ruby out in the open, here’s my solution for Project Euler Problem 35. 

For this solution, I played with pushing and popping on and off of a stack, err, Ruby array. And rotating the digits is brought to you by our good friend, shift. Execution time is slow (35 seconds) but it didn’t take me long to code so, once again, I’m happy with the result.

As always, any feedback is welcome.

# Euler 35
# http://projecteuler.net/index.php?section=problems&id=35
# The number, 197, is called a circular prime because all
# rotations of the digits: 197, 971, and 719, are
# themselves prime.
#
# There are thirteen such primes below 100:
# 2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73, 79, and 97.
#
# How many circular primes are there below one million?
timer_start = Time.now

require 'mathn'

def circular_prime?(i)
  nums = i.to_s.chars.to_a

  nums.length.times do
    return false if (!nums.join().to_i.prime?)
    # "pop" digit off the front and rotate to the end
    nums.push nums[0]
    nums.shift
  end

  return true
end

answer = 0
Prime.each { |x|
  break if x >= 1_000_000
  answer += 1 if circular_prime?(x)
}

puts answer
puts "Elapsed Time: #{(Time.now - timer_start)*1000} milliseconds"