rust code example - find prime numbers

prime.rs

use std::collections::HashMap;

fn primes(n: usize) -> Vec<usize> {
    if n < 2 {
        return vec![];
    }

    if n == 2 {
        return vec![2];
    }

    let mut odds = Vec::new();
    let mut i = 3;
    while i <= n {
        odds.push(i);
        i += 2;
    }

    let mut factors = HashMap::new();
    factors.insert(2, true);
    for n in &odds {
        factors.insert(*n, true);
    }

    for i in &odds {
        if !*(factors.get(i).unwrap()) {
            continue;
        }

        let mut k = *i + 2;
        while k <= n {
            if k % *i == 0 {
                factors.insert(k, false);
            }
            k += 2;
        }
    }

    let mut result = factors.into_iter().filter(|(_, v)| *v).map(|(k, _)| k).collect::<Vec<usize>>();
    result.sort();
    result
}

fn main() {
    // primes
    assert_eq!(primes(2), vec![2]);
    assert_eq!(primes(3), vec![2, 3]);
    assert_eq!(primes(5), vec![2, 3, 5]);
    assert_eq!(primes(13), vec![2, 3, 5, 7, 11, 13]);
    assert_eq!(primes(30), vec![2, 3, 5, 7, 11, 13, 17, 19, 23, 29]);
}