for len in (1..8) {
    var (pre="", post="")
    @^len -> permutations {|*p|
        var t = p.join
        post.append!(t) if !post.contains(t)
        pre.prepend!(t) if !pre.contains(t)
    }
    printf("%2d: %8d %8d\n", len, pre.len, post.len)
}