fn main() {
    let result = prime_factors(600851475143).into_iter().max();
    println!("Result: {}", result.unwrap());
}

fn prime_factors(number: i64) -> Vec<i64> {
    let mut factors = vec![2];
    let upper: i64 = (number as f64).sqrt().ceil() as i64;
    for i in 3..upper {
        let mut is_prime = true;
        for factor in factors.clone() {
            if i % factor == 0 {
                is_prime = false;
                break;
            }
        }
        if is_prime && number % i == 0 {
            factors.push(i);
        }
    }

    return factors;
}

#[cfg(test)]
mod tests {
    use crate::prime_factors;

    #[test]
    fn it_works() {
        let result = prime_factors(13195).into_iter().max();
        assert_eq!(result.unwrap(), 29);
    }
}