Lua洗牌算法：Fisher-Yates的等概率打乱

-- 错误：随机键排序伪洗牌，分布有偏
for _, c in ipairs(cards) do
    c.rnd = math.random()
end
table.sort(cards, function(a, b)
    return a.rnd < b.rnd
end)

local function shuffle(cards)
    for i = #cards, 2, -1 do
        local j = math.random(i)
        cards[i], cards[j] = cards[j], cards[i]
    end
    return cards
end
local hand = shuffle({"a", "b", "c", "d", "e"})
local label = panel:getChildByName("handText")
label:setString(table.concat(hand, ","))