Perfect Shuffle drill

# Perfect Shuffle

function ps(x::Array{<:Any, 1}) # perform a single perfect Shuffle
    n = length(x) # this should be even
    n2 = div(n, 2)
    z = Array{eltype(x)}(undef, n)

    for i = 1:n2
        j = 2*i
        z[j-1] = x[i]
        z[j] = x[n2+i]
    end

    return z
end

function main(x::Array{<:Any, 1}) # perform a series of ps until the original order reappears
    n = 1
    z = ps(x)

    while z != x
        z = ps(z)
        n += 1
    end

    return n
end