Chapter4_Loops_Ex16

import java.lang.Math;


/* ==================================
        chapter 4: Loops

        Ex16: friendly numbers
   ==================================
*/

public class MyProgram {

    /* function to get the sum of divisors */
    public static int getSum(int number){

        int maxD = (int)Math.sqrt(number); //loop's range is [2,√num]
        int sum=1; //every number can divide by 1
        int divisor; //represent divisors bigger than the search range

        for(int i = 2; i <= maxD; i++)
        {
            if(number % i == 0)
            {
                /*
                    if i divide the number:
                         - add i to sum
                         - init divisor
                */

                sum += i;
                divisor = number/i; //must be one of the divisors because the number can divide by i

                if(divisor!=i) //if the divisor is bigger than the loop's range → add divisor to sum
                    sum+=divisor;
            }
        }
        return sum;
    }


    public static void main(String[] args) {
        final int SIZE =10;
        int counter = 0;
        int num1,num2;

        for(num1=1;counter<SIZE;num1++){

            num2=getSum(num1);

            if( num2>num1 && (num1==getSum(num2) )  ) {
                //we found a match! they should get f*** married
                System.out.println(num1 + " and " + num2 + " are mates");
                counter++;
            }
        }
    }
}