task: concurrently compute and print the first 1000 prime numbers

main.rs

use std::env::args;

use rayon::prelude::*;

fn is_prime(n: u64, primes: &[u64]) -> bool {
    let sqrt = (n as f64).sqrt() as u64;
    for &p in primes {
        if p > sqrt {
            break;
        }
        if n % p == 0 {
            return false;
        }
    }
    true
}

fn main() {
    let mut primes: Vec<u64> = vec![2];
    let mut candidate = 3;
    

    let args: Vec<String> = args().collect();
    let prime_limit: usize = args.get(1).expect("Please enter the limit")
        .parse()
        .expect("Enter a valid number");

    while primes.len() < prime_limit {
        let batch: Vec<u64> = (candidate..candidate + 2000)
            .into_par_iter()
            .filter(|&n| {
                if n % 2 == 0 {
                    return false;
                }
                is_prime(n, &primes)
            })
            .collect();

        primes.extend(batch);
        candidate += 2000;
    }

    primes.truncate(prime_limit);
    for p in primes {
        println!("{}", p);
    }
}