Question

Q. How to write a recursive algorithm to find the largest prime factor of a number in java?

Answer 1

import java.io.*;

import java.util.*;

class GFG {

    // function to find largest prime factor

    static long maxPrimeFactors(long n)

    {

        // Initialize the maximum prime

        // factor variable with the

        // lowest one

        long maxPrime = -1;

        // Print the number of 2s

        // that divide n

        while (n % 2 == 0) {

            maxPrime = 2;

            // equivalent to n /= 2

            n >>= 1;

        }

        // n must be odd at this point,

        // thus skip the even numbers

        // and iterate only for odd

        // integers

        for (int i = 3; i <= Math.sqrt(n); i += 2) {

            while (n % i == 0) {

                maxPrime = i;

                n = n / i;

            }

        }

        // This condition is to handle

        // the case when n is a prime

        // number greater than 2

        if (n > 2)

            maxPrime = n;

        return maxPrime;

    }

    // Driver code

    public static void main(String[] args)

    {

        Long n = 15l;

        System.out.println(maxPrimeFactors(n));

        n = 25698751364526l;

        System.out.println(maxPrimeFactors(n));

    }

}

Output:

5
328513