use rand::{self, Rand, Rng, XorShiftRng};
pub fn vec<T>(size: usize, start: usize) -> Option<Vec<T>>
where
T: Rand,
{
if size > start + 2 {
let mut rng: XorShiftRng = rand::thread_rng().gen();
Some((0..size).map(|_| rng.gen()).collect())
} else {
None
}
}