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Java

Diego Murray
Diego Murray
2,515 Points
Posted by Diego Murray
Diego Murray
2,515 Points

Project Euler Problem 10 JAVA - Bug

Not sure why I don't get the right answer here...

public class Main {

    public static final int num = 2000000;

    public static void main(String[] args) {
        int sum = 0;
        for (int i = 0; i < num; i++) {
            if(isPrime(i)) {
                sum += i;
            }
        }

        System.out.println("Sum: " + sum);

    }

    public static boolean isPrime(int n) {
        if (n <= 1) {
            return false;
        }
        for (int i = 2; i < Math.sqrt(n); i++) {
            if (n % i == 0) {
                return false;
            }
        }
        return true;
    }

}
Diego Murray
Diego Murray
2,515 Points
Diego Murray
Diego Murray
2,515 Points

Looking for sum of all primes under 2 million.

1 Answer

Simon Coates
Simon Coates
28,693 Points
Simon Coates
Simon Coates
28,693 Points

Working on sums of primes under 10. Starting small so numbers are manageable.

public class Main {

    public static final int num = 10;

    public static void main(String[] args) {
        int sum = 0;
        for (int i = 0; i < num; i++) {
            if(isPrime(i)) {
                sum += i;
                System.out.println("Prime:"+i);
            }
        }
        System.out.println("Sum: " + sum);
    }

    public static boolean isPrime(int n) {
        if (n <= 1) {
            return false;
        }
        for (int i = 2; i < Math.sqrt(n); i++) {
            if (n % i == 0) {
                return false;
            }
        }
        return true;
    }
}

produces

Prime:2
Prime:3
Prime:4
Prime:5
Prime:7
Prime:9
Sum: 30

I'm guessing

public class Main {

    public static final int num = 10;

    public static void main(String[] args) {
        int sum = 0;
        for (int i = 0; i < num; i++) {
            if(isPrime(i)) {
                sum += i;
                System.out.println("Prime:"+i);
            }
        }
        System.out.println("Sum: " + sum);
    }

    public static boolean isPrime(int n) {
        if (n <= 1) {
            return false;
        }
        for (int i = 2; i <= Math.sqrt(n); i++) {
            if (n % i == 0) {
                return false;
            }
        }
        return true;
    }
}
Diego Murray
Diego Murray
2,515 Points
Diego Murray
Diego Murray
2,515 Points

I see now that it's collecting numbers that aren't Primes( ex. 2, 4). You posted the same code again, not sure if that was intentional..

Simon Coates
Simon Coates
28,693 Points
Simon Coates
Simon Coates
28,693 Points

there was a difference in the isPrime method. <= not <