Prime number check java

manpreet 3 years ago

To eliminate duplicates , use a Set

manpreet 3 years ago

Please show what you have tried, and why exactly it didn't work, in the smallest amount of code possible. We're here to help you solve a specific problem, not write your code for you.

manpreet 3 years ago

Try breaking down the problem into smaller chunks. I recommend making a few methods which each handle a small portion of the program. You can then test each of them individually. First make a method to check if a number is prime boolean isPrime(int i), then make method to reverse the number, int reverse(int i). Create a method boolean isReversePrime(int i) which calls both isPrime(i) and isPrime(reverse(i)), etc etc. Breaking down a problem into smaller steps may look like more work, but it makes your code much easier to read and also much easier to verify the correctness.

manpreet 3 years ago

Instead of checking till n, we can check till √n because a larger factor of n must be a multiple of smaller factor which all ready cover.

manpreet 3 years ago

You need to use TreeSet - which will contain only distinct ref="https://forum.tuteehub.com/tag/elements">elements and give result in sorted form. You can refer to following code-

Set<Integer> set = new TreeSet<>();
        for(ref="https://forum.tuteehub.com/tag/int">int i = 0; i < a.length; i++) {
            boolean isPrime = true;
            if(isPrime(a[i]) && isPrime(r[i]))
                set.add(a[i]);
        }

Also create a ref="https://forum.tuteehub.com/tag/function">function for checking prime numbers -

private static boolean isPrime(ref="https://forum.tuteehub.com/tag/int">int num) {
        for(ref="https://forum.tuteehub.com/tag/int">int i = 2; i <= num/2; ++i)
        {
            if(num % i == 0)
            {
               ref="https://forum.tuteehub.com/tag/return">return false;
            }
        }
        ref="https://forum.tuteehub.com/tag/return">return true;
    }