浏览足迹：最近看过的商品回看

-- 错误：重复插入不去重，足迹变复读机
function trackView(goodsId)
    table.insert(footprints, 1, goodsId)
end

local footprints = {}
local function trackView(goodsId)
    for i, id in ipairs(footprints) do
        if id == goodsId then
            table.remove(footprints, i)
        end
    end
    table.insert(footprints, 1, goodsId)
    if #footprints > 20 then
        table.remove(footprints)
    end
end