fn countdown_gm_update(x: u32) -> Vec<u32> {
    let mut vector = Vec::<u32>::new();
    //Still confuse why we need using 'mut v', if we just use v: &mut Vec<u32>
    // -> error: cannot borrow `v` as mutable, as it is not declared as mutable
    fn aux(x: u32, mut v: &mut Vec<u32>) {
        println!("{:p}", v);
        if x != 0 {
            v.push(x);
            aux(x-1, &mut v)
        }
    }
    aux(x, &mut vector);
    return vector;
}

fn main() {
    println!("{:?}", countdown_gm_update(10));
}