Project Euler Problem58

include Math

class Integer
  def prime?
    return false if self == 0 || self == 1
    (2..sqrt(self).to_i).all? { |i| self % i != 0 }
  end
end

def prime_cornars( h )
  [ h*h-(h-1)*3, h*h-(h-1)*2, h*h-(h-1) ].select { |elem| elem.prime? }
end

def main( maxh = 100000 )
  (1..maxh).inject([0, 1]) do |ratio, n|
    h = n * 2 + 1

    ratio[0] += prime_cornars(h).size
    ratio[1] += 4

    return h if ratio[0] / ratio[1].to_f < 0.1
    ratio
  end
end

puts main