#![allow(unused_variables)]
fn main() {
    use std::collections::VecDeque;
    let mut buf: VecDeque<_> = (0..10).collect();
    buf.rotate_left(3);
    assert_eq!(buf, [3, 4, 5, 6, 7, 8, 9, 0, 1, 2]);
    for i in 1..10 {
        assert_eq!(i * 3 % 10, buf[0]);
        buf.rotate_left(3);
    }
    assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
}