Daily Programmer 370 Easy first shot solution.

dp370e.rs

// Given a slice of upc digits, return the checksum
fn upc_raw(input: &[u8]) -> u8 {
    let mut code = Vec::from(input);

    while code.len() < 11 {
        code.insert(0, 0);
    }
    if code.len() > 11 {
        code.resize(11, 0);
    }

    let even: u8 = code.iter().step_by(2).sum();
    let odd: u8 = code.iter().skip(1).step_by(2).sum();

    (10 - ((even * 3 + odd) % 10)) % 10
}

// Given a upc string, return the checksum
fn upc_str(input: &str) -> u8 {
    let raw: Vec<u8> = input.chars().map(|i| i.to_digit(10).unwrap() as u8).collect();
    upc_raw(&raw)
}

// Given a upc string as a single number, return the checksum
fn upc(input: u64) -> u8 {
    upc_str(&input.to_string())
}

fn main() {
    for &input in &[4210000526, 3600029145, 12345678910, 1234567] {
        println!("upc({}) => {}", input, upc(input));
    }
}