cassidoo-newsletter/luhn/src/main.rs

fn main() {
    println!("{}", validate(vec![1, 2, 3, 4, 5, 6, 7, 8, 9]));
}

fn validate(card: Vec<u8>) -> bool {
    let mut card = card;
    let given_check = card.pop().unwrap();

    let mut check = 0;
    for (i, n) in card.iter().rev().enumerate() {
        check += match i & 1 == 0 {
            true => {
                if *n > 4 {
                    (*n * 2) - 9
                } else {
                    *n * 2
                }
            }
            false => *n,
        };
    }

    10 - (check % 10) == given_check
}