Why is my program saying that the integer number is too large for Project Euler #3 (Java)?

Question

Here is my code:

public static boolean isPrime(long num)
    {
        for(long i=2; i<=num/2; i++)
        {
            if(num%i==0)
            {
                return false;
            }
        }
        return true;
    }

    public static long findLargestPrimeFactor(long n)
    {
        long max=0;
        for(long factor=2; factor<n; factor++)
        {
            if(n % factor==0)
            {
                if(isPrime(n/factor)==true)
                {
                    max=factor;
                }
            }
        }
        return max;
    }

However, when I run it, it says that the integer 600851475143 is too large. can anyone help me?

I don't see any reference to that number in your code. Are you getting a runtime exception? What is "it" that gives you this message? — Matt Ball, Sep 25 '13 at 04:28
How are you calling your `findLargestPrimeFactor` method and where are you seeing this error? — rocketboy, Sep 25 '13 at 04:32

James · Answer 1 · 2013-09-25T04:55:13.347

I'm going to wager you're calling

 isLargestPrimeFactor(600851475143);

since that's the problem given in Project Euler #3. This will fail to compile with an error:

  error: integer number too large: 600851475143

Correct? If that's the case, try:

 isLargestPrimeFactor(600851475143L);

The "L" suffix tells the compiler that you mean it to be a long literal, not an int (otherwise the compiler will treat it as an integer literal, and it's too large to fit in an int)

Why is my program saying that the integer number is too large for Project Euler #3 (Java)?

1 Answers1