
pub fn print(n: i32) -> Option<String> {
    fn print_line(v: &mut Vec<u8>, width: usize, max_width: usize) {
        v.extend(repeat(b' ').take((max_width - width) / 2));
        v.extend(repeat(b'*').take(width));
        v.push(b'\n');
    }

    if n < 0 || n % 2 == 0 {
        return None;
    }
    let n = n as usize;