to find sum of primes up to 2 million

Question

I am trying to find the sum of all prime numbers <=2 million so i used sieve of Eratosthenes TO mark all prime numbers .As i declared the boolean array of size 2 million ,i got this error

             "main" java.lang.ArrayIndexOutOfBoundsException: 2000000

Since the sum can be two large so i used long instead of sum .here is the code in java

public class Summationofprimes {
    static  long[] isprime=new long[2000000];

     static void sieve(){
         Arrays.fill(isprime, 0);//all marked false
         isprime[1]=1;isprime[0]=1;
         for(int i=2;i*i<=2000000;i++){
             if(isprime[i]==0){
                // print(i);
                // sum+=i;
                //print(sum);
                 for(int j = i * i; j <= 2000000 ;j += i){
                     isprime[j]=1;// all multiples marked true 
                 }
             }
         }


    }

    public static void main(String[] args) {
        sieve();
        long sum=0;
        System.out.println("sum is :");
        for(int i=2;i<=2000000;i++){
            if(isprime[i]==0){
                sum+=i;


        }
        }
        System.out.println(sum);
        // TODO Auto-generated method stub

    }

}

How do i fix this issue in code ?

Shouldn't it be `for(int j = i; ...` in your inner loop? – Frank Puffer Aug 26 '16 at 12:18 — Frank Puffer, Aug 26 '16 at 12:18

score 1 · Answer 1 · answered Aug 26 '16 at 12:14

1

Here you go :

static  long[] isprime=new long[2000001];

Now it has range from 0 to 2000000

answered Aug 26 '16 at 12:14

libik

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it worked,i had done it wrong earlier – naamnhibataynge Aug 26 '16 at 12:19
Since we already know that 2000000 is not a prime, another and slightly nicer solution would be to use `< 2000000` rather than `<= 2000000`. – Ole V.V. Aug 26 '16 at 12:30

to find sum of primes up to 2 million

1 Answers1