find the sum of the multiples of 3 and 5 below 1000

Question

Ok guys, so I'm doing the Project Euler challenges and I can't believe I'm stuck on the first challenge. I really can't see why I'm getting the wrong answer despite my code looking functional:

import java.util.ArrayList;


public class Multithree {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        ArrayList<Integer> x = new ArrayList<Integer>();
        ArrayList<Integer> y = new ArrayList<Integer>();
        int totalforthree = 0;
        int totalforfive = 0;

        int total =0;

        for(int temp =0; temp < 1000 ; temp++){
            if(temp % 3 == 0){
                x.add(temp);
                totalforthree += temp;
            }
        }

        for(int temp =0; temp < 1000 ; temp++){
            if(temp % 5 == 0){
                y.add(temp);
                totalforfive += temp;
            }
        }

        total = totalforfive + totalforthree;



        System.out.println("The multiples of 3 or 5 up to 1000 are: " +total);

    }

}

I'm getting the answer as 266333 and it says it's wrong...

Answer 1

you should use the same for loop for both to aviod double counting numbers that are multiple of both. such as 15,30...

   for(int temp =0; temp < 1000 ; temp++){
        if(temp % 3 == 0){
            x.add(temp);
            totalforthree += temp;
        }else if(temp % 5 == 0){
            y.add(temp);
            totalforfive += temp;
        }
    }