fn main() {
    let squares: Vec<_> = (1..10).map(|n| n*n).collect();
    let is_square = |num| squares.binary_search(&num).is_ok();

    for i in 1..100 {
        let state = if is_square(i) {"open"} else {"closed"};
        println!("Door {} is {}", i, state);
    }
}