using Printf

function makesofn(n::Integer)
    buf = Vector{typeof(n)}(0)
    i = 0
    return function sofn(item)
        i += 1
        if i ≤ n
            push!(buf, item)
        else
            j = rand(1:i)
            if j ≤ n buf[j] = item end
        end
        return buf
    end
end

nhist = zeros(Int, 10)
for _ in 1:10^5
    kas = makesofn(3)
    for j in 0:8 kas(j) end
    for k in kas(9) nhist[k+1] += 1 end
end

println("Simulating sof3(0:9) 100000 times:")
for (i, c) in enumerate(nhist)
    @printf("%5d → %5d\n", i-1, c)
end