use std::cmp;
use std::collections::LinkedList;

fn add(a: &LinkedList<usize>, b: &LinkedList<usize>) -> LinkedList<usize> {
    let mut aiter = a.iter().rev();
    let mut biter = b.iter().rev();

    let mut tmp = 0;
    let mut output = Vec::new();

    loop {
        match (aiter.next(), biter.next()) {
            (Some(x), Some(y)) => tmp += x + y,
            (Some(x), None) | (None, Some(x)) => tmp += x,
            _ => break
        }

        let mut tmp2 = tmp;
        if tmp >= 10 {
            tmp2 -= 10;
            tmp = 1;
        } else {
            tmp = 0;
        }

        output.push(tmp2)
    }

    output.into_iter()
        .rev()
        .collect()
}


fn main() {
    let a = vec![1, 2, 3, 4].into_iter()
        .collect::<LinkedList<usize>>();
    let b = vec![5, 6].into_iter()
        .collect::<LinkedList<usize>>();

    let sum = add(&a, &b);
    println!("{:?}", sum);
}