# Shobute☘

## Project-Euler / 10

Find the sum of all the primes below two million.

Here’s my solution in Java:

public class Problem10 {
public static void main(String[] args) {
int max = 2_000_000;
boolean[] isComposite = new boolean[max + 1];
for (int i = 2; i * i <= max; i++) {
if (!isComposite[i]) {
for (int j = i; i * j <= max; j++) isComposite[i*j] = true;
}
}
long sum = 0;
for (int i = 2; i <= max; i++) if (!isComposite[i]) sum += i;
System.out.println(sum);
}
}


It uses the sieve of Eratosthenes algorithm. It could be optimized by using the sieve of Atkin, and/or using a bit vector instead of a boolean array, but as is it runs in a very fast time.

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