Sieve of Eratosthenes in Ruby

Question

Rather than scraping a Ruby version of this algorithm off the net I wanted to create my own based on its description here. However I cannot figure out two things

<         


        

Answer 1

The following seems to work. I took out the floating point arithmetic and squared instead of square rooting. I also replaced the deletion loop with a "select" call.

while primes[index]**2 <= primes.last
      prime = primes[index]
      primes = primes.select { |x| x == prime || x%prime != 0 }
      index += 1
end

Edit: I think I figured out how you're trying to do this. The following seems to work, and seems to be more in line with your original approach.

while Math.sqrt(primes.last).ceil >= primes[index]
    (primes[index] * 2).step(primes.last, primes[index]) do
      |x|
      primes.delete(x)
    end
    index += 1
end