Gold Bach

Q1_2018.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Q1_2018 {

    static int n = 0;
    static int primes[];

    public static void main(String[] args) throws IOException {
        InputStreamReader ir = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(ir);


        System.out.println("Enter the Number");
        n = Integer.parseInt(br.readLine());
        primes = new int[n];

        if (isValid()) {

            oddPrimeArray();
            //cycling through the array in the most efficient way to pick out all the viable combinations.

            for (int i = 0; i < primes.length; ++i) {
                for (int j = i; j < primes.length; ++j) {
                    if (primes[i] + primes[j] == n)
                        System.out.println(primes[i] + " " + primes[j]);
                }
            }


        }
        else
            System.out.println("Invalid!");

    }

    static boolean isValid() {
        return n > 9 && n < 50;
    }

    static void oddPrimeArray() {
        int k = 0;

        for (int i = 1; i <= n; ++i) {
            int c = 0;
            for (int j = 1; j <= i; ++j) {
                if (i % j == 0) {
                    ++c;
                }
            }
            if (c == 2) {
                //now checking for odd
                if (i % 2 != 0) {
                    primes[k] = i;
                    ++k;
                }
            }
        }
    }


}