ProjectEuler: Summation of Primes

app.d

import std.stdio : writefln;

void main() {
    "%,3?d".writefln('_', 2_000_000.sumOfPrimesBelow);
}

ulong sumOfPrimesBelow(ulong num) {
    // Create a dynamic array of booleans initialized to true
    bool[] primes = new bool[num];
    primes[] = true;

    // Set 0 and 1 to false (not primes)
    primes[0] = false;
    primes[1] = false;

    ulong sum = 0;

    // Sieve of Eratosthenes
    for (ulong p = 2; p < num; p++) {
        if (primes[p]) {
            sum += p;
            for (ulong m = p * p; m < num; m += p) {
                primes[m] = false;
            }
        }
    }

    return sum;
}