Question

I’m trying to create a boolean recursive function which accepts 1 parameter only and doesn’t act as a wrapper for another function, that checks whether a number contains a pair of combinations which are both primes.

For example, the possible combinations for 8379 are:

8 379  
83 79  
837 9

I’ve managed to create the function using a wrapper function, but I can’t seem to be able to do it without a wrapper.

What I currently have is:

func(num):  
num is prime -> return true
else -> call func(num / 10, num % 10).

fun(num1, num2):  
num1 and num2 are primes -> return true  
num1 < 10 -> return false  
return func(num1 / 10, concat(num1 % 10, num2))

Answer 1

Writing in Java.

I’m not quite sure if you want to check for “multiple” combinations of the number or just one.

Here’s my recursive function for checking just one combination’s existence. If I addressed your requirement incorrectly, please leave a comment.

public static boolean splitPrime(int n, int pow10) {
        return (isPrime(n / pow10) && isPrime(n % pow10))
                || (pow10  < n/10 && splitPrime(n, pow10 * 10));
    }

Invoke it using splitPrime(n,10)