Problem 3

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?

Solution

#The prime factors of 13195 are 5, 7, 13 and 29.

#What is the largest prime factor of the number 600851475143?

 

 

def PrimeFactor(number)

    isPrime = true;

    factors = Array.new

    factorCandidate = Math.sqrt(number).floor

    while factorCandidate > 1 do

        if number % factorCandidate == 0  then

            isPrime = false;

            #kinda like the ‘push’ syntax here

            PrimeFactor(factorCandidate).each {|factor| factors << factor }

            PrimeFactor(number / factorCandidate).each {|factor| factors << factor }

        end

        factorCandidate -= 1

    end

    if isPrime then

        factors.Add(number)

    end

    factors

end

 

factors = PrimeFactor(600851475143)

puts factors.max

 

 

Discussion

Even though I copied and pasted my C# solution here it still took me a while to iron out the kinks.  There are some things I really enjoy about the syntax so far, but I still haven’t discovered the virtue of dynamic typing.  Maybe I will as time passes.

If you have questions, leave a comment or please find me on Twitter (@azzlsoft) or email (rich@azzlsoft.com).