local fmt = require "fmt"

local function knuth_shuffle(a)
    for i = #a, 2, -1 do
        local j = math.random(i)
        a[i], a[j] = a[j], a[i]
    end
end

local tests = { {}, {10}, {10, 20}, {10, 20, 30}, {10, 20, 30, 40} }
for tests as a  do
    local b = a:clone()
    knuth_shuffle(a)
    print($"{fmt.swrite(b)} -> {fmt.swrite(a)}")
end