Code shared from the Rust Playground

playground.rs

fn collatz(mut n: u64) -> Option<u64> {
    let mut step = 0;
    if n == 0 {
        return None;
    }
    
    while n != 1 {
        if n % 2 == 0 {
            n /= 2;
        } else {
            n = 3 * n + 1;
        }
        step += 1;
    }
    Some(step)
}