Project Euler #10

extern crate num;
use num::BigUint;
use num::traits::Zero;
use std::time::Instant;

fn main() {
    let begin = Instant::now();

    let primes = find_primes(|p, n| n >= 2000000);

    let time = begin.elapsed();
    println!("Time elapsed: {}s", time.as_secs());

    let n = primes.len();
    let p_max = primes.last().unwrap();
    println!("Search done. Found {} primes, the highest being {}.", n, p_max);

    let mut sum: BigUint = Zero::zero();

    for p in &primes {
        sum += BigUint::from(*p);
    }

    println!("The sum of the primes is {}.", sum);
}

fn find_primes<F>(exit: F) -> Vec<u64>
    where F: Fn(&Vec<u64>, u64) -> bool
{
    let mut primes: Vec<u64> = vec![2];
    let mut n = 3;

    while !exit(&primes, n) {
        let mut is_prime = true;
        for p in &primes {
            if n % p == 0 {
                is_prime = false;
                break;
            }
            if *p as f64 >= (n as f64).sqrt() {
                break;
            }
        }
        if is_prime {
            primes.push(n);

            if primes.len() % 10000 == 0 {
                println!("n = {:6}; p_n = {:7}", primes.len(), n);
            }
        }
        n += 2;
    }
    primes
}