struct Node { at: i64, first: i64, next: i64 }
struct Ctx<'a> {
    source: &'a [u8], nodes: &'a mut Vec<Node>,
    text: &'a mut Vec<u8>, scratch: &'a mut Vec<i64>,
}
fn walk(c: &mut Ctx<'_>, n: i64, depth: i64) -> i64 {
    let n = usize::try_from(n).unwrap();
    let mark = c.scratch.len();
    c.scratch.push(depth);
    let at = usize::try_from(c.nodes[n].at).unwrap();
    c.text.push(c.source[at]);
    let mut total = c.scratch[mark];
    let mut e = c.nodes[n].first;
    while e >= 0 {
        total += walk(c, e, depth + 1);
        e = c.nodes[usize::try_from(e).unwrap()].next;
    }
    c.scratch.truncate(mark);
    total
}
fn compile(source: &[u8]) -> i64 {
    let mut nodes=vec![Node {at:0,first:1,next:-1},
                       Node {at:1,first:-1,next:2}, Node {at:2,first:-1,next:-1}];
    let mut text=Vec::new(); let mut scratch=Vec::new();
    let mut c=Ctx {source,nodes:&mut nodes,text:&mut text,scratch:&mut scratch};
    let r=walk(&mut c,0,1);
    use std::io::Write;
    let mut out=std::io::stdout().lock();out.write_all(&text).unwrap();
    writeln!(&mut out," {}",scratch.len()).unwrap();
    r
}

fn main() {assert_eq!(compile(b"abc"),5);}