Question

2. Primes [2 marks] A prim e p > 1 has no factors other than 1, so p%m 0 for all m є {2.3, p-1). Test all the integers greater than 1 that you can, and identify the primes (again, write your own code). How far can you get in 10 minutes (use a clock or watch to approximately time this)? Print (or write) the last three primes that you find, and also check them using a web tool (Google "prime checker"). Advanced (no extra marks): you only need to check up to P, and you only need to check the primes you have already found up to vp

Answer 1

// Code to find as much Prime numbers within ten minutes

import java.util.Vector;

public class PrimeIn10Minutes {
    public static void main(String[] args)
    {
        boolean flag = false;

        long startTime;
        startTime = System.currentTimeMillis();

        Vector vector = new Vector();

        long num = 2;

        while((System.currentTimeMillis() - startTime) <= 600000)
        {
            flag = checkNextPrime(num);

            if (!flag)
            {
                vector.add(num);
            }
            num++;
        }

        int vectorSize = vector.size();

        System.out.println("Last three prime numbers till ten minutes are :");
        for(int i = vectorSize-1; i > vectorSize-4; i--)
        {
            System.out.println(vector.get(i));
        }
    }

    public static boolean checkNextPrime(long num)
    {
        boolean flag = false;

        if(num/2 < 2)
            return false;

        else {
            for(long i = 2; i <= num/2; i++)
            {
                if(num % i == 0)
                {
                    flag = true;
                    break;
                }
            }
            return flag;
        }
    }
}

Output:

Last three prime numbers till ten minutes are :
1074253
1074251
1074223