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

What is the largest prime factor of the number 600851475143 ?
– Project Euler Problem 3

There are two ways to solve this:

  1. brute force (default option)
  2. user our brains (e.g. unique factorization)

Let’s stick to a brute force approach (with some logical enhancements inside) and allow for arbitrary numbers N:


function isPrime(n::UInt64)
	isPrimeNumber::Bool = true;
	for i in 2:1:(n-1)
		if n%i == 0
			isPrimeNumber = false;
			return isPrimeNumber
		end
	end
	return isPrimeNumber
end


function largestPrimeBF(N::UInt64)
	#=
	# Brute Force (BF) approach to determine if a number is a prime number or not
	#
	# 
	=#
	largestPrime::UInt64 = 0;
	sqrtN = trunc(UInt64,sqrt(N));
	for n in 2:1:sqrtN
		if N%n == 0
			isPrimeNumber = isPrime(n)
			if isPrimeNumber
				largestPrime = n;
			end
		end
	end
	return largestPrime
end


function findPrimeMax(N::UInt64)
	highestPrime = largestPrimeBF(N);
	return highestPrime
end


function parseARGS()
		if isempty(ARGS)
			N::UInt64 = 600851475143;
		else
			N = tryparse(UInt64,ARGS[1]);
		
		end
		return  N
end



function main()
	N  = parseARGS();
	result = findPrimeMax(N);
	println(result);
end

main()


julia ProjectEuler0003.jl

6857

julia ProjectEuler0003.jl 5564347583489823423

47975801

Well, that looks good!