Euler Problem #3 in Ruby - Find largest prime factor

euler3.rb

def big_prime(x)
  prime = x
  (2..Math.sqrt(x).to_i).each do |i|
    break if prime <= i
    prime /= i while (prime > i && prime % i == 0)
  end
  prime
end

s = Time.new
puts big_prime(600851475143)
puts "elapsed: #{Time.new-s}"

A little slower but now works for even numbers too. Could be optimized further but would violate the first rule of optimization.

Interesting. This takes longest for prime numbers. Methinks this may have applicability in encryption algorithms...