Pass

[violaso]

Very well done Felix!

Yeah, your are right. Your tree is not only slow, but lack functions such as size. These tests are also interestingly named:

#[test]
fn tree_is_balanced() {
    //...
    assert_eq!(b, 0);
}

#[test]
fn tree_is_really_balanced() {
    //...
    assert_eq!(b, 0);
}

I would have liked you to instead have one test for assert_eq!(b, 0) and one for assert_eq!(b, 1).

Sad spagetti:

// get input lines as iterative
//let lines: Vec<String> = input
//    .lock()
//    .lines()
//    .map(|_line| _line.ok().unwrap())
//    .collect();