use std::cell::Cell;
use std::collections::HashMap;

pub type Id = i64;

struct Node<'a> {
  pub id: Id,
  pub next: Cell<Option<&'a Node<'a>>>
}

struct RawNode {
  pub id: Id,
  pub next: Id
}

fn main() {
  let raw_nodes = vec![
    RawNode { id: 1, next: 2},
    RawNode { id: 2, next: 1}
  ];

  let nodes = build_nodes(&raw_nodes);

  for (id, node) in nodes {
    println!("{} -> {}", id, node.next.get().and_then(|n| Some(n.id)).unwrap_or(-1));
  }
}

fn build_nodes<'a>(raw_nodes: &Vec<RawNode>) -> HashMap<Id, Node<'a>> {
  let mut nodes = HashMap::new();

  for raw_node in raw_nodes {
    let node = Node {
      id: raw_node.id,
      next: Cell::new(None)
    };
    nodes.insert(node.id, node);
  }

  for raw_node in raw_nodes {
    let node = nodes.get(&raw_node.id).unwrap();
    let next = nodes.get(&raw_node.next).unwrap();

    node.next.set(Some(next));
  }

  nodes
}