euler7.rs

euler7.rs

fn nth_primes(n: usize) -> usize {
    match n {
        0 => 1,
        1 => 2,
        2 => 3,
        _ => {
            let mut primes = vec![2, 3];
            let mut candidate = 5;
            loop {
                let max = (candidate as f64).sqrt() as usize;
                let mut prime = true;
                for d in primes.iter().skip(1) {
                    if *d > max {
                        break;
                    }
                    if candidate % *d == 0 {
                        prime = false;
                        break;
                    }
                }
                if prime {
                    primes.push(candidate);
                    if primes.len() == n {
                        return candidate;
                    }
                }
                candidate += 2;
            }
        },
    }
}

fn main() {
    println!("6th prime: {}", nth_primes(6));
    println!("10 001th prime: {}", nth_primes(10001));
}