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Thread: Wondering if there's a way to make this more efficient.

  1. #1
    Member mjr's Avatar
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    Default Wondering if there's a way to make this more efficient.

    I have the following method for determining whether or not an integer value is a prime number:

    public boolean isPrime(int value){
        if(value < 2)
            return false;
        else 
        {
            int xSquareRoot = (int)Math.sqrt((double)value);
     
            for (int x = 3; x <= xSquareRoot; x+=2)
                if(value % x == 0)
                    return false;
        }
        return true;
    }

    The for loop seems like it would be a waste of time and resources, and that it would be inefficient.

    I'm just wondering if there's maybe a way I could make this more efficient. I mean, it works very quickly now, but it just seems like iterating over every odd number up to the integer square root of a number seems like a resource drain, especially for large primes, where the code would have to do several thousand iterations.


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    Default Re: Wondering if there's a way to make this more efficient.

    Take a look at this link. Your algorithm falls under the "Naive methods" and can be improved.

    Do they not have google where you're at? This took about 30 seconds to find.
    Need Java help? Check out the HotJoe Java Help forums!

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    Super Moderator Sean4u's Avatar
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    Default Re: Wondering if there's a way to make this more efficient.

    Remember if your function argument is int or smaller and your function return value is int or smaller, that there's *by definition* a static alternative on reasonably common hardware. Your "boolean isPrime(int)" for example could be implemented as a 128MB array. I'm not suggesting you add a 128MB object to your project, just responding to your question as-asked.

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