Finds the largest prime factor of a given integer, up to 1024.

largest_prime_1024.rb

# Finds the largest prime factor of a given integer.
# Up to 1024 for sake of efficiency.

def find_factors(number)
	factors = Array.new

	for x in 1..number
		factors << x if number % x == 0
	end

	return factors
end

def is_prime(number)
	maximum = Math.sqrt(number)
	for x in 2..maximum
		if number % x == 0
			return false
		end
	end

	return true
end

print "Integer up to 1024: "
number = gets.chomp.to_i

if number > 1024 || number < 1
	print "Defaults to 1024\n"
	number = 1024
end

factors = find_factors(number)

big_prime_factor = 0
while big_prime_factor == 0
	if is_prime(factors.last)
		big_prime_factor = factors.last
	else
		factors.delete(factors.last)
	end
end

puts big_prime_factor