euler_35.rb

def find_prime(n)
  return false if n <= 1
  2.upto(Math.sqrt(n).to_i) do |x|
    return false if n%x == 0
  end
  true
end
large = []
1.upto(1000000) { |each_num| large[each_num] = true if find_prime(each_num) }
count = 0
1.upto(1000000) do |num|
  str = num.to_s
  all = (0...str.length).collect { |i| large[((str * 2)[i, str.length]).to_i] ? true : false }
  count+=1 if all.inject(0){|b,i| b&&=i}
end
puts "The count of such primes is #{count}"